Archived posts from the 'Crawler Directives' Category

Get a grip on the Robots Exclusion Protocol (REP)

REP command hierarchyThanks to the very nice folks over at SEOmoz I was able to prevent this site from becoming a kind of REP/robots.txt blog. Please consider reading this REP round up:

Robots Exclusion Protocol 101

My REP 101  links to the various standards (robots.txt, REP tags, Sitemaps, microformats) the REP consists of, and provides a rough summary of each REP component. It explains the difference between crawler directives and indexer directives, and which command hierarchy search engines follow when REP directives put in different levels conflict.

Educate yourself on the REPWhy do I think that solid REP knowledge is important right now? Not only because of the confusion that exists thanks to the volume of crappy advice provided at every Webmaster hangout. Of course understanding the REP makes webmastering easier, thus I’m glad when my REP related pamphlets are considered somewhat helpful.

I’ve a hidden agenda, though. I predict that the REP is going to change shortly. As usual, its evolvement is driven by a major search engine, since the W3C and such organizations don’t bother with the conglomerate of quasi standards and RFCs known as the Robots Exclusion Protocol. In general that’s not a bad thing. Search engines deal with the REP every day, so they have a legitimate interest.

Unfortunately not every REP extension that search engines have invented so far is useful for Webmasters, some of them are plain crap. Learning from fiascos and riots of the past, the engines are well advised to ask Webmasters for feedback before they announce further REP directives.

I’ve a feeling that shortly a well known search engine will launch a survey regarding particular REP related ideas. I want that Webmasters are well aware of the REP’s complexity and functionality when they contribute their take on REP extensions. So please educate yourself. :)

My pamphlet discussing a possible standardization of REP tags as robots.txt directives could be a useful reference, also please watch the great video here. ;)



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Getting URLs outta Google - the good, the popular, and the definitive way

Keep out GoogleThere’s more and more robots.txt talk in the SEOsphere lately. That’s a good thing in my opinion, because the good old robots.txt’s power is underestimated. Unfortunately it’s quite often misused or even abused too, usually because folks don’t fully understand the REP (by following “advice” from forums instead of reading the real thing, or at least my stuff ).

I’d like to discuss the REP’s capabilities assumed to make sure that Google doesn’t index particular contents from three angles:

The good way
If the major search engines would support new robots.txt directives that Webmasters really need, removing even huge chunks of content from Google’s SERPs –without collateral damage– via robots.txt would be a breeze.
The popular way
Shamelessly stealing Matt’s official advice [Source: Remove your content from Google by Matt Cutts]. To obscure the blatant plagiarism, I’ll add a few thoughts.
The definitive way
Of course that’s not the ultimate way, but that’s the way Google’s cookies crumble, currently. In other words: Google is working on a leaner approach, but that’s not yet announced, thus you can’t use it; you still have to jump through many hoops.

The good way

Caution: Don’t implement code from this section, the robots.txt directives discussed here are not (yet/fully) supported by search engines!

Currently all robots.txt statements are crawler directives. That means that they can tell behaving search engines how to crawl a site (fetching contents), but they’ve no impact on indexing (listing contents on SERPs). I’ve recently published a draft discussing possible REP tags for robots.txt. REP tags are indexer directives known from robots meta tags and X-Robots-Tags, which –as on-page respectively per-URL directives– require crawling.

The crux is that REP tags must be assigned to URLs. Say you’ve a gazillion of printer friendly pages in various directories that you want to deindex at Google, putting the “noindex,follow,noarchive” tags comes with a shitload of work.

How cool would be this robots.txt code instead:
Noindex: /*printable
Noarchive: /*printable

Search engines would continue to crawl, but deindex previously indexed URLs respectively not index new URLs from
/articles/printable/*.htm
/manuals/printable/*.pdf
/products/descriptions/*.php?format=printable&product=*
...

provided those URLs aren’t disallow’ed. They would follow the links in those documents, so that PageRank gathered by printer friendly pages wouldn’t be completely wasted. To apply an implicit rel-nofollow to all links pointing to printer friendly pages, so that those can’t accumulate PageRank from internal or external links, you’d add
Norank: /*printable

to the robots.txt code block above.

If you don’t like that search engines index stuff you’ve disallow’ed in your robots.txt from 3rd party signals like inbound links, and that Google accumulates even PageRank for disallow’ed URLs, you’d put:
Disallow: /unsearchable/
Noindex: /unsearchable/
Norank: /unsearchable/

To fix URL canonicalization issues with PHP session IDs and other tracking variables you’d write for example
Truncate-variable sessionID: /

and that would fix the duplicate content issues as well as the problem with PageRank accumulated by throw-away URLs.

Unfortunately, robots.txt is not yet that powerful, so please link to the REP tags for robotx.txt “RFC” to make it popular, and proceed with what you have at the moment.

Matt Cutts was kind enough to discuss Google’s take on contents excluded from search engine indexing in 10 minutes or less here:

You really should listen, the video isn’t that long.

In the following I’ve highlighted a few methods Matt has talked about:

Don’t link (very weak)
Although Google usually doesn’t index unlinked stuff, this can happen due to crawling based on sitemaps. Also, the URL might appear in linked referrer stats on other sites that are crawlable, and folks can link from the cold.
.htaccess / .htpasswd (Matt’s first recommendation)
Since Google cannot crawl password protected contents, Matt declares this method to prevent content from indexing safe. I’m not sure what will happen when I spread a few strong links to somebody’s favorite smut collection, perhaps I’ll test some day whether Google and other search engines list such a reference on their SERPs.
robots.txt (weak)
Matt rightly points out that Google’s cool robots.txt validator in the Webmaster Console is a great tool to develop, test and deploy proper robots.txt syntax that effectively blocks search engine crawling. The weak point is, that even when search engines obey robots.txt, they can index uncrawled content from 3rd party sources. Matt is proud of Google’s smart capabilities to figure out suiteble references like the ODP. I agree totally and wholeheartedly. Hence robots.txt in its current shape doesn’t prevent content from showing up in Google and other engines as well. Matt didn’t mention Google’s experiments with Noindex: support in robots.txt, which need improvement but could resolve this dilemma.
Robots meta tags (Google only, weak with MSN/Yahoo)
The REP tag “noindex” in a robots meta element prevents from indexing, and, once spotted, deindexes previously listed stuff - at least at Google. According to Matt Yahoo and MSN still list such URLs as references without snippets. Because only Google obeys “noindex” totally by wiping out even URL-only listings and foreign references, robots meta tags should be considered a kinda weak approach too. Also, search engines must crawl a page to discover this indexer directive. Matt adds that robots meta tags are problematic, because they’re buried on the pages and sometimes tend to get forgotten when no longer needed (Webmasters might do forget to take the tag down, respectively add it later on when search engines policies change, or work in progress gets released respectively outdated contents are taken down). Matt forgot to mention the neat X-Robots-Tags that can be used to apply REP tags in the HTTP header of non-HTML resources like images or PDF documents. Google’s X-Robots-Tag is supported by Yahoo too.
Rel-nofollow (kind of weak)
Although condoms totally remove links from Google’s link graphs, Matt says that rel-nofollow should not be used as crawler or indexer directive. Rel-nofollow is for condomizing links only, also other search engines do follow nofollow’ed links and even Google can discover the link destination from other links they gather on the Web, or grab from internal links inadvertently lacking a link condom. Finally, rel-nofollow requires crawling too.
URL removal tool in GWC (Matt’s second recommendation)
Taking Matt’s enthusiasm while talking about Google’s neat URL terminator into account, this one should be considered his first recommendation. Google provides tools to remove URLs from their search index since five years at least (way longer IIRC). Recently the Webmaster Central team has integrated those, as well as new functionality, into the Webmaster Console, donating it a very nice UI. The URL removal tools come with great granularity, and because the user’s site ownership is verified, it’s pretty powerful, safe, and shows even the progress for each request (the removal process lasts a few days). Its UI is very flexible and allows even revoking of previous removal requests. The wonderful little tool’s sole weak point is that it can’t remove URLs from the search index forever. After 90 days or possibly six months the erased stuff can pop up again.

Summary: If your site isn’t password protected, and you can’t live with indexing of disallow’ed contents, you must remove unwanted URLs from Google’s search index periodically. However, there are additional procedures that can support –but not guarantee!– deindexing. With other search engines it’s even worse, because those don’t respect the REP like Google, and don’t provide such handy URL removal tools.

The definitive way

Actually, I think Matt’s advice is very good. As long as you don’t need a permanent solution, and if you lack the programming skills to develop such a beast that works with all (major) search engines. I mean everybody can insert a robots meta tag or robots.txt statement, and everybody can semiyearly repeat URL removal requests with the neat URL terminator, but most folks are scared when it comes to conditional manipulation of HTTP headers to prevent stuff from indexing. However, I’ll try to explain quite safe methods that actually work (with Apache, not IIS) in the following examples.

First of all, if you really want that search engines don’t index your stuff, you must allow them to crawl it. And no, that’s not an oxymoron. At the moment there’s no such thing as an indexer directive on site-level. You can’t forbid indexing in robots.txt. All indexer directives require crawling of the URLs that you want to keep out of the SERPs. Of course that doesn’t mean you should serve search engine crawlers a book from each forbidden URL.

Lets start with robots.txt. You put
User-agent: *
Disallow: /images/
Disallow: /movies/
Disallow: /unsearchable/
 
User-agent: Googlebot
Disallow:
Allow: /
 
User-agent: Slurp
Disallow:
Allow: /

The first section is just a fallback.

(Here comes a rather brutal method that you can use to keep search engines out of particular directories. It’s not suitable to deal with duplicate content, session IDs, or other URL canonicalization. More on that later.)

Next edit your .htaccess file.
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_URI} ^/unsearchable/
RewriteCond %{REQUEST_URI} !\.php
RewriteRule . /unsearchable/output-content.php [L]
</IfModule>

If you’ve .php pages in /unsearchable/ then remove the second rewrite condition, put output-content.php into another directory, and edit my PHP code below so that it includes the PHP scripts (don’t forget to pass the query string).

Now grab the PHP code to check for search engine crawlers here and include it below. Your script /unsearchable/output-content.php looks like:
<?php
@include("crawler-stuff.php"); // defines variables and functions
$isSpider = checkCrawlerIP ($requestUri);
if ($isSpider) {
@header("HTTP/1.1 403 Thou shalt not index this", TRUE, 403);
@header("X-Robots-Tag: noindex,noarchive,nosnippet,noodp,noydir");
exit;
}
 
$arr = explode("#", $requestUri);
$outputFileName = $arr[0];
$arr = explode("?", $outputFileName);
$outputFileName = $_SERVER["DOCUMENT_ROOT"] .$arr[0];
if (substr($outputFileName, -1, 1) == "/") {
$outputFileName .= "index.html";
}
if (file_exists($outputFileName)) {
// send the content type header
$contentType = "text/plain";
if (stristr($outputFileName, ".html")) $contentType ="text/html";
if (stristr($outputFileName, ".css")) $contentType ="text/css";
if (stristr($outputFileName, ".js")) $contentType ="text/javascript";
if (stristr($outputFileName, ".png")) $contentType ="image/png";
if (stristr($outputFileName, ".jpg")) $contentType ="image/jpeg";
if (stristr($outputFileName, ".gif")) $contentType ="image/gif";
if (stristr($outputFileName, ".xml")) $contentType ="application/xml";
if (stristr($outputFileName, ".pdf")) $contentType ="application/pdf";
@header("Content-type: $contentType");
@header("X-Robots-Tag: noindex,noarchive,nosnippet,noodp,noydir");
readfile($outputFileName);
exit;
}
 
// That’s not the canonical way to call the 404 error page. Don’t copy, adapt:
@header("HTTP/1.1 307 Oups, I displaced $outputFileName", TRUE, 307);
@header("Location: http://sebastians-pamphlets.com/404/");
exit;
?>

What does the gibberish above do? In .htaccess we rewrite all requests for resources stored in /unsearchable/ to a PHP script, which checks whether the request is from a search engine crawler or not.

If the requestor is a verified crawler (known IP or IP and host name belong to a major search engine’s crawling engine), we return an unfriendly X-Robots-Tag and an HTTP response code 403 telling the search engine that access to our content is forbidden. The search engines should assume that a human visitor receives the same response, hence they aren’t keen on indexing these URLs. Even if a search engine lists an URL on the SERPs by accident, it can’t tell the searcher anything about the uncrawled contents. That’s unlikely to happen actually, because the X-Robots-Tag forbids indexing (Ask and MSN might ignore these directives).

If the requestor is a human visitor, or an unknown Web robot, we serve the requested contents. If the file doesn’t exist, we call the 404 handler.

With dynamic content you must handle the query string and (expected) cookies yourself. PHP’s readfile() is binary safe, so the script above works with images or PDF documents too.

If you’ve an original search engine crawler coming from a verifiable server feel free to test it with this page (user agent spoofing doesn’t qualify as crawler, come back in a week or so to check whether the engines have indexed the unsearchable stuff linked above).

The method above is not only brutal, it wastes all the juice from links pointing to the unsearchable site areas. To rescue the PageRank, change the script as follows:

$urlThatDesperatelyNeedsPageRank = "http://sebastians-pamphlets.com/about/";
if ($isSpider) {
@header("HTTP/1.1 301 Moved permanently", TRUE, 301);
@header("Location: $urlThatDesperatelyNeedsPageRank");
exit;
}

This redirects crawlers to the URL that has won your internal PageRank lottery. Search engines will/shall transfer the reputation gained from inbound links to this page. Of course page by page redirects would be your first choice, but when you block entire directories you can’t accomplish this kind of granularity.

By the way, when you remove the offensive 403-forbidden stuff in the script above and change it a little more, you can use it to apply various X-Robots-Tags to your HTML pages, images, videos and whatnot. When a search engine finds an X-Robots-Tag in the HTTP header, it should ignore conflicting indexer directives in robots meta tags. That’s a smart way to steer indexing of bazillions of resources without editing them.

Ok, this was the cruel method; now lets discuss cases where telling crawlers how to behave is a royal PITA, thanks to the lack of indexer directives in robots.txt that provide the required granularity (Truncate-variable, Truncate-value, Order-arguments, …).

Say you’ve session IDs in your URLs. That’s one (not exactly elegant) way to track users or affiliate IDs, but strictly forbidden when the requestor is a search engine’s Web robot.

In fact, a site with unprotected tracking variables is a spider trap that would produce infinite loops in crawling, because spiders following internal links with those variables discover new redundant URLs with each and every fetch of a page. Of course the engines found suitable procedures to dramatically reduce their crawling of such sites, what results in less indexed pages. Besides joyless index penetration there’s another disadvantage - the indexed URLs are powerless duplicates that usually rank beyond the sonic barrier at 1,000 results per search query.

Smart search engines perform high sophisticated URL canonicalization to get a grip on such crap, but Webmasters can’t rely on Google & Co to fix their site’s maladies.

Ok, we agree that you don’t want search engines to index your ugly URLs, duplicates, and whatnot. To properly steer indexing, you can’t just block the crawlers’ access to URLs/contents that shouldn’t appear on SERPs. Search engines discover most of those URLs when following links, and that means that they’re ready to assign PageRank or other scoring of link popularity to your URLs. PageRank / linkpop is a ranking factor you shouldn’t waste. Every URL known to search engines is an asset, hence handle it with care. Always bother to figure out the canonical URL, then do a page by page permanent redirect (301).

For your URL canonicalization you should have an include file that’s available at the very top of all your scripts, executed before PHP sends anything to the user agent (don’t hack each script, maintaining so many places handling the same stuff is a nightmare, and fault-prone). In this include file put the crawler detection code and your individual routines that handle canonicalization and other search engine friendly cloaking routines.

View a Code example (stripping useless query string variables).

How you implement the actual canonicalization routines depends on your individual site. I mean, if you’ve not the coding skills necessary to accomplish that you wouldn’t read this entire section, wouldn’t you?

    Here are a few examples of pretty common canonicalization issues:

  • Session IDs and other stuff used for user tracking
  • Affiliate IDs and IDs used to track the referring traffic source
  • Empty values of query string variables
  • Query string arguments put in different order / not checking the canonical sequence of query string arguments (ordering them alphabetically is always a good idea)
  • Redundant query string arguments
  • URLs longer than 255 bytes
  • Server name confusion, e.g. subdomains like “www”, “ww”, “random-string” all serving identical contents from example.com
  • Case issues (IIS/clueless code monkeys handling GET-variables/values case-insensitive)
  • Spaces, punctuation, or other special characters in URLs
  • Different scripts outputting identical contents
  • Flawed navigation, e.g. passing the menu item to the linked URL
  • Inconsistent default values for variables expected from cookies
  • Accepting undefined query string variables from GET requests
  • Contentless pages, e.g. outputted templates when the content pulled from the database equals whitespace or is not available

Summary

Hiding contents from all search engines requires programming skills that many sites can’t afford. Even leading search engines like Google don’t provide simple and suitable ways to deindex content –respectively to prevent content from indexing– without collateral damage (lost/wasted PageRank). We desperately need better tools. Maybe my robots.txt extensions are worth an inspection.



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My plea to Google - Please sanitize your REP revamps

Standardization of REP tags as robots.txt directives

Google is confules on REP standards and robots.txtThis draft is kinda request for comments for search engine staff and uber search geeks interested in the progress of Robots Exclusion Protocol (REP) standardization (actually, every search engine maintains their own REP standard). It’s based on/extends the robots.txt specifications from 1994 and 1996, as well as additions supported by all major search engines. Furthermore it considers work in progress leaked out from Google.

In the following I’ll try to define a few robots.txt directives that Webmasters really need.

Show Table of Contents

Currently Google experiments with new robots.txt directives, that is REP tags like “noindex” adapted for robots.txt. That’s a welcomed and brilliant move.

Unfortunately, they got it totally wrong, again. (Skip the longish explanation of the rel-nofollow fiasco and my rant on Google’s current robots.txt experiments.)

Google’s last try to enhance the REP by adapting a REP tag’s value in another level was a miserable failure. Not because crawler directives on link-level are a bad thing, the opposite is true, but because the implementation of rel-nofollow confused the hell out of Webmasters, and still does.

Rel-Nofollow or how Google abused standardization of Web robots directives for selfish purposes

Don’t get me wrong, an instrument to steer search engine crawling and indexing on link level is a great utensil in a Webmaster’s toolbox. Rel-nofollow just lacks granularity, and it was sneakily introduced for the wrong purposes.

Recap: When Google launched rel-nofollow in 2005, they promoted it as a tool to fight comment spam.

From now on, when Google sees the attribute (rel=”nofollow”) on hyperlinks, those links won’t get any credit when we rank websites in our search results. This isn’t a negative vote for the site where the comment was posted; it’s just a way to make sure that spammers get no benefit from abusing public areas like blog comments, trackbacks, and referrer lists.

Technically spoken, this translates to “search engine crawlers shall/can use rel-nofollow links for discovery crawling, but indexers and ranking algos processing links must not credit link destinations with PageRank, anchor text, nor other link juice originating from rel-nofollow links”. Rel=”nofollow” meant rel=”pass-no-reputation”.

All blog platforms implemented the beast, and it seemed that Google got rid of a major problem (gazillions of irrelevant spam links manipulating their rankings). Not so the bloggers, because the spammers didn’t bother to check whether a blog dofollows inserted links or not. Despite all the condomized links the amount of blog comment spam increased dramatically, since the spammers were forced to attack even more blogs in order to earn the same amount of uncondomized links from blogs that didn’t update to a software version that supported rel-nofollow.

Experiment failed, move on to better solutions like Akismet, captchas or ajax’ed comment forms? Nope, it’s not that easy. Google had a hidden agenda. Fighting blog comment spam was just a snake oil sales pitch, an opportunity to establish rel-nofollow by jumping on a popular band wagon. In 2005 Google had mastered the guestbook spam problem already. Devaluing comment links in well structured pages like blog posts is as easy as doing the same with guestbook links, or identifying affiliate links. In other words, when Google launched rel-nofollow, blog comment spam was definitely not a major search quality issue any more.

Identifying paid links on the other hand is not that easy, because they often appear as editorial links within the content. And that was a major problem for Google, a problem that they weren’t able to solve algorithmically without cooperation of all webmasters, site owners, and publishers. Google actually invented rel-nofollow to get a grip on paid links. Recently they announced that Googlebot no longer follows condomized links (pre-Bigdaddy Google followed condomized links and indexed contents discovered from rel-nofollow links), and their cold war on paid links became hot.

Of course the sneaky morphing of rel-nofollow from “pass no reputation” to a full blown “nofollow” is just a secondary theater of war, but without this side issue (with regard to REP standardization) Google would have lost, hence it was decisive for the outcome of their war on paid links.

To stay fair, Danny Sullivan said twice that rel-nofollow is Dave Winer’s fault, and Google as the victim is not to blame.

Rel-nofollow is settled now. However, I don’t want to see Google using their enormous power to manipulate the REP for selfish goals again. I wrote this rel-nofollow recap because probably, or possibly, Google is just doing it once more:

Google’s “Noindex: in robots.txt” experiment

Google supports a Noindex: directive in robots.txt. It seems Google’s Noindex: blocks crawling like Disallow:, but additionally prevents URLs blocked with Noindex: both from accumulating PageRank as well as from indexing based on 3rd party signals like inbound links.

This functionality would be nice to have, but accomplishing it with “Noindex” is badly wrong. The REP’s “Noindex” value without an explicit “Nofollow” means “crawl it, follow its links, but don’t list it on SERPs”. With pagel-level directives (robots meta tags and X-Robots-Tags) Google handles “Noindex” exactly as defined, that means with an implicit “Follow”. Not so in robots.txt. Mixing crawler directives (Disallow:) with indexer directives (Noindex:) this way takes the “Follow” out of the game, because a search engine can’t follow links from uncrawled documents.

Webmasters will not understand that “Nofollow” means totally different things in robots.txt and meta tags. Also, this approach steals granularity that we need, for example for use with technically structured sitemap pages and other hubs.

According to Google their current interpretation of Noindex: in robots.txt is not yet set in stone. That means there’s an opportunity for improvement. I hope that Google, and other search engines as well, listen to the needs of Webmasters.

Dear Googlers, don’t take the above said as Google bashing. I know, and often wrote, that Google is the search engine that puts the most efforts in boring tasks like REP evolvement. I just think that a dog company like Google needs to take real-world Webmasters into the boat when playing with standards like the REP, for the sake of the cats. ;)

Recap: Existing robots.txt directives

The /path example in the following sections refers to any way to assign URIs to REP directives, not only complete URIs relative to the server’s root. Patterns can be useful to set crawler directives for a bunch of URIs:

  • *: any string in path or query string, including the query string delimiter “?”, multiple wildcards should be allowed.
  • $: end of URI
  • Trailing /: (not exactly a pattern) addresses a directory, its files and subdirectories, the subdirectorie’s files etc., for example
    • Disallow: /path/
      matches /path/index.html but not /path.html
    • /path
      matches both /path/index.html and /path.html, as well as /path_1.html. It’s a pretty common mistake to “forget” the trailing slash in crawler directives meant to disallow particular directories. Such mistakes can result in blocking script/page-URIs that should get crawled and indexed.

Please note that patterns aren’t supported by all search engines, for example MSN supports only file extensions (yet?).

User-agent: [crawler name]
Groups a set of instructions for a particular crawler. Crawlers that find their own section in robots.txt ignore the User-agent: * section that addresses all Web robots. Each User-agent: section must be terminated with at least one empty line.

Disallow: /path
Prevents from crawling, but allows indexing based on 3rd party information like anchor text and surrounding text of inbound links. Disallow’ed URLs can gather PageRank.

Allow: /path
Refines previous Disallow: statements. For example
Disallow: /scripts/
Allow: /scripts/page.php

tells crawlers that they may fetch http://example.com/scripts/page.php or http://example.com/scripts/page.php?article=1, but not any other URL in http://example.com/scripts/.

Sitemap: [absolute URL]
Announces XML sitemaps to search engines. Example:
Sitemap: http://example.com/sitemap.xml
Sitemap: http://example.com/video-sitemap.xml

points all search engines that support Google’s Sitemaps Protocol to the sitemap locations. Please note that sitemap autodiscovery via robots.txt doesn’t replace sitemap submissions. Google, Yahoo and MSN provide Webmaster Consoles where you not only can submit your sitemaps, but follow the indexing process (wishful thinking WRT particular SEs). In some cases it might be a bright idea to avoid the default file name “sitemap.xml” and keep the sitemap URLs out of robots.txt, sitemap autodiscovery is not for everyone.

Recap: Existing REP tags

REP tags are values that you can use in a page’s robots meta tag and X-Robots-Tag. Robots meta tags go to the HTML document’s HEAD section
<meta name="robots" content="noindex, follow, noarchive" />

whereas X-Robots-Tags supply the same information in the HTTP header
X-Robots-Tag: noindex, follow, noarchive

and thus can instruct crawlers how to handle non-HTML resources like PDFs, images, videos, and whatnot.

    Widely supported REP tags are:

  • INDEX|NOINDEX - Tells whether the page may be indexed (listed on SERPs) or not
  • FOLLOW|NOFOLLOW - Tells whether crawlers may follow links provided in the document or not
  • ALL|NONE - ALL = INDEX, FOLLOW (default), NONE = NOINDEX, NOFOLLOW
  • NOODP - tells search engines not to use page titles and descriptions pulled from DMOZ on their SERPs.
  • NOYDIR - tells Yahoo! search not to use page titles and descriptions from the Yahoo! directory on the SERPs.
  • NOARCHIVE - Google specific, used to prevent archiving (cached page copy)
  • NOSNIPPET - Prevents Google from displaying text snippets for your page on the SERPs
  • UNAVAILABLE_AFTER: RFC 850 formatted timestamp - Removes an URL from Google’s search index a day after the given date/time

Problems with REP tags in robots.txt

REP tags (index, noindex, follow, nofollow, all, none, noarchive, nosnippet, noodp, noydir, unavailable_after) were designed as page-level directives. Setting those values for groups of URLs makes steering search engine crawling and indexing a breeze, but also comes with more complexity and a few pitfalls as well.

  • Page-level directives are instructions for indexers and query engines, not crawlers. A search engine can’t obey REP tags without crawling the resource that supplies them. That means that not a single REP tag put as robots.txt statement shall be misunderstood as crawler directive.

    For example Noindex: /path must not block crawling, not even in combination with Nofollow: /path, because there’s still the implicit “archive” (= absence of Noarchive: /path). Providing a cached copy even of a not indexed page makes sense for toolbar users.

    Whether or not a search engine actually crawls a resource that’s tagged with “noindex, nofollow, noarchive, nosnippet” or so is up to the particular SE, but none of those values implies a Disallow: /path.

  • Historically, a crawler instruction on HTML element level overrules the robots meta tag. For example when the meta tag says “follow” for all links on a page, the crawler will not follow a link that is condomized with rel=”nofollow”.

    Does that mean that a robots meta tag overrules a conflicting robots.txt statement? Of course not in any case. Robots.txt is the gatekeeper, and so to say the “highest REP instance”. Actually, to this question there’s no absolute answer that satisfies everybody.

    A Webmaster sitting on a huge conglomerate of legacy code may want to totally switch to robots.txt directives, that means search engines shall ignore all the BS in ancient meta tags of pages created in the stone age of the Internet. Back then the rules were different. An alternative/secondary landing page’s “index,follow” from 1998 most probably doesn’t fly with 2008’s duplicate content filters and high sophisticated link pattern analytics.

    The Webmaster of a well designed brand new site on the other hand might be happy with a default behavior where page-level REP tags overrule site-wide directives in robots.txt.

  • REP tags used in robots.txt might refine crawler directives. For example a disallow’ed URL can accumulate PageRank, and may be listed on SERPs. We need at least two different directives ruling PageRank caluculation and indexing for uncrawlable resources (see below under Noodp:/Noydir:, Noindex: and Norank:).

    Google’s current approach to handle this with the Noindex: directive alone is not acceptable, we need a new REP tag to handle this case. Next up, when we introduce a new REP tag for use in robots.txt, we should allow it in meta tags and HTTP headers too.

  • In theory it makes no sense to maintain a directive that describes a default behavior. But why has the REP “follow” although the absence of “nofollow” perfectly expresses “follow”? Because of the way non-geeks think (try to explain why the value nil/null doesn’t equal empty/zero/blank to a non-geek. Not!).

    Implicit directives that aren’t explicitely named and described in the rules don’t exist for the masses. Even in the 10 commandments someone had to write “thou shalt not hotlink|scrape|spam|cloak|crosslink|hijack…” instead of a no-brainer like “publish unique and compelling content for people and make your stuff crawlable”. Unfortunately, that works the other way round too. If a statement (Index: or Follow:) is dependent on another one (Allow: respectively the absence of Disallow:) folks will whine, rant and argue when search engines ignore their stuff.

    Obviously we need at least Index:, Follow: and Archive to keep the standard usable and somewhat understandable. Of course crawler directives might thwart such indexer directives. Ignorant folks will write alphabetically ordered robots.txt files like
    Disallow: /cgi-bin/
    Disallow: /content/
    ...
    Follow: /cgi-bin/redirect.php
    Follow: /content/links/
    ...
    Index: /content/articles/

    without Allow: /content/links/, Allow: /content/articles/ and Allow: /cgi-bin/redirect.

    Whether or not indexer directives that require crawling can overrule the crawler directive Disallow: is open for discussion. I vote for “not”.

  • Applying REP tags on site-level would be great, but it doesn’t solve other problems like the need of directives on block and element level. Both Google’s section targeting as well as Yahoo’s robots-nocontent class name aren’t acceptable tools capable to instruct search engines how to handle content in particular page areas (advertising blocks, navigation and other templated stuff, links in footers or sidebar elements, and so on).

    Instead of editing bazillions of pages, templates, include files and whatnot to insert rel-nofollow/nocontent stuff for the sole purpose of sucking up to search engines, we need an elegant way to apply such micro-directives via robots.txt, or at least site-wide sets of instructions referenced in robots.txt. Once that’s doable, Webmasters will make use of such tools to improve their rankings, and not alone to comply to the ever changing search engine policies that cost the Webmaster community billions of man hours each year.

    I consider these robots.txt statements sexy:
    Nofollow a.advertising, div#adblock, span.cross-links: /path
    Noindex .inherited-properties, p#tos, p#privacy, p#legal: /path

    but that’s a wish list for another post. However, while designing site-wide REP statements we should at least think of block/element level directives.

Remember the rel-nofollow fiasco where a REP tag was used on HTML element level producing so much confusion and conflicts. Lets learn from past mistakes and make it perfect this time. A perfect standard can be complex, but it’s clear and unambiguous.

Priority settings

The REP’s command hierarchy must be well defined:

  1. robots.txt
  2. Page meta tags and X-Robots-Tags in the HTTP header. X-Robots-Tag values overrule conflicting meta tag values.
  3. [Future block level directives]
  4. Element level directives like rel-nofollow

That means, when crawling is allowed, page level instructions overrule robots.txt, and element level (or future block level) directives overrule page level instructions as well as robots.txt. As long as the Webmaster doesn’t revert the latter:

Priority-page-level: /path
Default behavior, directives in robots meta tags overrule robots.txt statements. Necessary to reset previous Priority-site-level: statements.

Priority-site-level: /path
Robots.txt directives overrule conflicting directives in robots meta tags and X-Robots-Tags.

Priority-site-level All: /path
Robots.txt directives overrule all directives in robots meta tags or provided elsewhere, because those are completely ignored for all URIs under /path. The “All” parameter would even dofollow nofollow’ed links when the robots.txt lacks corresponding Nofollow: statements.

Noindex: /path

Follow outgoing links, archive the page, but don’t list it on SERPs. The URLs can accumulate PageRank etcetera. Deindex previously indexed URLs.

[Currently Google doesn’t crawl Noindex’ed URLs and most probably those can’t accumulate PageRank, hence URLs in /path can’t distribute PageRank. That’s plain wrong. Those URLs should be able to pass PageRank to outgoing links when there’s no explicit Nofollow:, nor a “nofollow” meta tag respectively X-Robots-Tag.]

Norank: /path

Prevents URLs from accumulating PageRank, anchor text, and whatever link juice.

Makes sense to refine Disallow: statements in company with Noindex: and Noodp:/Noydir:, or to prevent TOS/contact/privacy/… pages and alike from sucking PageRank (nofollow’ing TOS links and stuff like that to control PageRank flow is fault-prone).

Nofollow: /path

The uber-link-condom. Don’t use outgoing links, not even internal links, for discovery crawling. Don’t credit the link destinations with any reputation (PageRank, anchor text, and whatnot).

Noarchive: /path

Don’t make a cached copy of the resource available to searchers.

Nosnippet: /path

List the resource with linked page title on SERPs, but don’t create a text snippet, and don’t reprint the description meta tag.

[Why don’t we have a REP tag saying “use my description meta tag or nothing”?]

Nopreview: /path

Don’t create/link an HTML preview of this resource. That’s interesting for subscriptions sites and applies mostly to PDFs, Word documents, spread sheets, presentations, and other non-HTML resources. More information here.

Noodp: /path

Don’t use the DMOZ title nor the DMOZ description for this URL on SERPs, not even when this resource is a non-HTML document that doesn’t supply its own title/meta description.

Noydir: /path

I’m not sure this one makes sense in robots.txt, because only Yahoo search uses titles and descriptions from the Yahoo directory. Anyway: “Don’t overwrite the page title listed on the SERPs with information pulled from the Yahoo directory, although I paid for it.”

Unavailable_after [date]: /path

Deindex the resource the day after [date]. The parameter [date] is put in any date or date/time format, if it lacks a timezone then GMT is assumed.

[Google’s RFC 850 obsession is somewhat weird. There are many ways to put a timestamp other than “25-Aug-2007 15:00:00 EST”.]

Truncate-variable [string|pattern]: /path

Truncate-value [string|pattern]: /path

In the search index remove the unwanted variable/value pair(s) from the URL’s query string and transfer PageRank and other link juice to the matching URL without those parameters. If this “bare URL” redirects, or is uncrawlable for other reasons, index it with the content pulled from the page with the more complex URL.

Regardless whether the variable name or the variable’s value matches the pattern, “Truncate_*” statements remove a complete argument from the query string, that is &variable=value. If after the (last) truncate operation the query string is empty, the querystring delimiter “?” (questionmark) must be removed too.

Order-arguments [charset]: /path

Sort the query strings of all dynamic URLs by variable name, then within the ordered variables by their values. Pick the first URL from each set of identical results as canonical URL. Transfer PageRank etcetera from all dupes to the canonical URL.

Lots of sites out there were developed by coders who are utterly challenged by all things SEO. Most Web developers don’t even know what URL canonicalization means. Those sites suffer from tons of URLs that all serve identical contents, just because the query string arguments are put in random order, usually inventing a new sequence for each script, function, or include file. Of course most search engines run high sophisticated URL canonicalization routines to prevent their indexes from too much duplicate content, but those algos can fail because every Web site is different.

I totally can resist to suggest a Canonical-uri /: /Default.asp statement that gathers all IIS default-document-URI maladies. Also, case issues shouldn’t get fixed with Case-insensitive-uris: / but by the clueless developers in Redmond.

Will all this come true?

Well, Google has silently started to support REP tags in robots.txt, it totally makes sense both for search engines as well as for Webmasters, and Joe Webmaster’s life would be way more comfortable having REP tags for robots.txt.

A better question would be “will search engines implement REP tags for robots.txt in a way that Webmasters can live with it?”. Although Google launched the sitemaps protocol without significant help from the Webmaster community, I strongly feel that they desperately need our support with this move.

Currently it looks like they will fuck up the REP, respectively the robots.txt standard, hence go grab your AdWords rep and choke her/him until s/he promises to involve Larry, Sergey, Matt, Adam, John, and the whole Webmaster Support Team for the sake of common sense and the worldwide Webmaster community. Thank you!



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Google to change the Robots Exclusion Protocol again

Google jumping the sharkWeb crawler directives, partly standardized in the Robots Exclusion Protocol (REP), evolved since 1994. Nowadays we’ve to deal with a conglomerate of not binding de facto standards and microformats, all of them extended by various organizations. All search engines claim that they obey “the standard”, but they refer to their very own REP implementation. In fact, each search engine supports a proprietary set of REP directives, differently from other players as a rule.

Google is the search engine putting the most efforts into Robots Exclusion Protocol (REP) evolvements. Their XML Sitemaps handling submissions instead of crawl restrictions changed the REP to a wider scope, the X-Robots-Tag brought us robots meta tags for non-HTML resources like PDF documents, images or video clips, and with Unavailable_after Google made a few clueless news sites happy. With the rel-nofollow microformat on the other hand, respectively its sneaky morphing from a spam fighting tool to its current shape, Google made nobody happy. Yahoo contributed the well meant but half-assed “robots-nocontent” class name, and of course “noydir” (it’s unlikely that any other engine will support those).

Now Google is working on new robots.txt syntax, and I am, politely put, not amused. Here is why I fear that Google is going to totally mess up the REP:

Google supports a “Noindex:” directive in robots.txt, which is treated as “Disallow:”1). Of course that’s an experiment, but if this behavior doesn’t change we’ll get a beast that is –with regard to the confusion it will produce– way more evil than the rel-nofollow fiasco.

  • A noindex-alias for disallow makes no sense, even when such syntax errors are out there.
  • Mixing crawler directives (allow/disallow) with indexer directives (noindex) is not always a bright idea. It’s bad enough that most Webmasters still believe that “Googlebot ranks their stuff”. (Actually, in some cases it can make sense. For example “nofollow” in robots meta tags (or at least for Google in REL attributes too) is both a crawler instruction as well as an indexer directive.)
  • Noindex and disallow are completely different commands. The REP’s noindex directive means “crawl it, follow its links, but don’t list it on the SERPs”. Disallow forbids crawling, but allows indexing URLs from directory listings or other inbound links.

Standards should be clear and unambiguous. Google must not redefine syntax and semantics that were in widespread use before Google even existed. I admit they’ve the power to fuck up the REP, but they also have “do no evil”.

Considering that Google is run by a bunch of smart engineers, I hope that they’ll do the right thing eventually. The right thing in this case is giving more power to REP evolvements, before questionable and selfish anti-search initiatives like ACAP ruin both the robots.txt consensus as well as the robots meta tag standard.

My idea of more power to REP evolvements is:

  • Sensible implementation of crawler/indexer-directives adapted from REP tags  in robots.txt. Applying page-level instructions ((no)index, (no)follow, noarchive, nosnippet, noodp/noydir, unavailable_after and hopefully nopreview) to groups of URIs is a great way to steer crawling and indexing, especially for sites which for various reasons cannot make use of the HTTP header’s X-Robots-Tag.
  • Implementation of block-level directives in robots.txt. Allowing Webmasters to apply crawler instructions like “noindex” or “nofollow” to particular page areas, like advertising blocks, duplicated text or repetitive navigation elements, addressed via HTML element names and class names and/or DOM-IDs, would be a very flexible instrument to steer crawling and indexing, and it could eleminate many points of failure.
  • Getting Webmasters, Publishers, SEOs and all major engines together to discuss possibly missing granularity and to develop a binding norm obeyed by all players.

The last one sounds like wishful thinking. The alternative is that Google (and, if possible, the bigger engines) talk with Webmasters and then launch the necessary REP extensions. The other engines will follow sooner or later. The publishers, although not getting all their desired ACAP restrictions, will be happy too. Standards like the Robots Exclusion Protocol should be developed by engineers.


1) Noindex: is not a plain Disallow:, there’s an interesting difference. In Google’s experiment both directives block crawling, but Disallow: allows URL-indexing based on 3rd party information, and Disallow:‘ed URLs can accumulate PageRank from internal as well as external links. Noindex:‘ed URLs on the other hand will not appear on SERPs as URL-only listing or with an ODP title and snippet, and I’m quite sure that they will not gather PageRank nor other link juice. That means links from any pages to such URLs get an implicit rel-nofollow in Google’s PageRank calculation, just like dangling links. This apparatus could be a great way to handle PageRank leaks (monthly blog archives, printer friendly pages and stuff like that), because shit happens, hence some links to such pages will slip through without condom. I admit that’s a neat idea, but its implementation is flawed because it doesn’t consider the implicit Follow: (that’s syntax Google doesn’t support in robots.txt). A better way to mark site areas which shall not gather PageRank without raping the REP would be a Norank: directive or so. Noindex: without a Nofollow: must not block crawling. Googlebot must fetch those URLs to follow their links.



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Validate your robots.txt - Googlebot becomes smarter

Validate your robots.txt!Last week I reported that Google experiments with new crawler directives for use in robots.txt. Today Google has confirmed that Googlebot understands experimental REP syntax like Noindex:.

That means that forgotten –and, until recently, ignored– statements in your robots.txt might change the crawler’s behavior all of a sudden, without notice. I don’t know for sure which experimental crawler directives Google has implemented, but for example a line like
Noindex: /
in your robots.txt will now deindex your complete Web site.

“Noindex:” is not defined in the Robots Exclusion Protocol from 1994, and not mentioned in Google’s official documents.

John Müller from Google Zürich states:

At the moment we will usually accept the “noindex” directive in the robots.txt, but we are not yet at a point where we are willing to set it into stone and announce full support.

[…] I just want to remind everyone again that this is something that may still change over time. Be careful when playing with things like this.

My understanding of “be careful” is:

  • Create a separate section for Googlebot. Do not rely on directives addressing all Web robots. Especially when you’ve a Googlebot section already, Google’s crawler will ignore directives set under “all user agents” and process only the Googlebot section. Repeat all statements under User-agent: * in User-agent: Googlebot to make sure that Googlebot obeys them.
  • RTFM
  • Do not use other crawler directives than
    Disallow:
    Allow:
    Sitemap:
    in the Googlebot section.
  • Don’t mess-up pattern matching.
    * matches a sequence of characters
    $ specifies the end of the URL
    ? separates the path from the query string, you can’t use it as wildcard!
  • Validate your robots.txt with the cool robots.txt analyzer in your Google Webmaster Console.

Folks put the funniest stuff into their robots.txt, for example images or crawl delays like “Don’t crawl this site during our office hours”. Crawler directives from robots meta tags aren’t very popular, but they appear in many robots.txt files. Hence it makes sound sense to use what people express, regardless the syntax errors.

Also, having the opportunity to manage page specific crawler directives like “noindex”, “nofollow”, “noarchive” and perhaps even “nopreview” on site level is a huge time saver, and eliminates many points of failure. Kudos to Google for this initiative, I hope it will make it into the standards.

I’ll test the experimental robots.txt directives and post the results. Perhaps I’ll set up a live test like this one.

Take care.


Update: Here is the live test of suspected respectively desired new crawler directives for robots.txt. I’ve added a few unusual statements to my robots.txt and uploaded scripts to monitor search engine crawling. The test pages provide links to search queries so you can check whether Google indexed them or not.

Please don’t link to the crawler traps, I’ll update this post with my findings. Of course I appreciate links, so here is the canonical URL:
http://sebastians-pamphlets.com/validate-your-robots-txt-or-google-might-deindex-your-site/#live-robots-txt-test

Please note that you should not make use of the crawler directives below on production systems! Bear in mind that you can achive all that with simple X-Robots-Tags in the HTTP headers. That’s a bullet-proof way to apply robots meta tags to files without touching them, and it works with virtual URIs too. X-Robots-Tags are sexy, but many site owners can’t handle them due to various reasons, whereas corresponding robots.txt syntax would be usable for everybody (not suffering from restrictive and/or free hosts).

Noindex:

robots.txt:
Noindex: /repstuff/noindex.php

Expected behavior:
No crawling/indexing. It seems Google interprets “Nofollow:” as “Disallow:”.
Desired behavior:
“Follow:” is the REP’s default, hence Google should fetch everything and follow the outgoing links, but shouldn’t deliver Noindex’ed contents on the SERPs, not even as URL-only listings.
Google’s robots.txt validator:
http://sebastians-pamphlets.com/repstuff/noindex.php Blocked by line 30: Noindex: /repstuff/noindex.php
Status:
See test page
Google’s crawler / indexer:
2007-11-21: crawled (possibly caused by an outdated robots.txt cache).
2007-11-23: indexed and cached.
2007-11-21: crawled a page linked only from noindex.php.
2007-11-23: indexed and cached a page linked only from noindex.php.
(If an outdated robots.txt cache falsely allowed crawling, the search result(s) should disappear shortly after the next crawl.)
2007-11-26: deindexed, the same goes for the linked page (without recrawling).
2007-12-07: appeared under “URLs restricted by robots.txt” in GWC.
2007-12-17: I consider this case closed. Noindex: blocks crawling, deindexes previously indexed pages, and is suspected to block incoming PageRank.

Nofollow:

robots.txt:
Nofollow: /repstuff/nofollow.php

Expected behavior:
Crawling, indexing, and following the links as if there’s no “Nofollow:”.
Desired behavior:
Crawling, indexing, and ignoring outgoing links.
Google’s robots.txt validator:
Line 31: Nofollow: /repstuff/nofollow.php Syntax not understood
http://sebastians-pamphlets.com/repstuff/nofollow.php Allowed
Status:
See test page
Google’s crawler / indexer:
2007-11-21: crawled.
2007-11-23: indexed and cached.
2007-11-21: crawled a page linked only from nofollow.php (21 Nov 2007 23:19:37 GMT, for some reason not logged properly).
2007-11-23: indexed and cached a page linked only from nofollow.php.
2007-11-26: recrawled, deindexed, no longer cached. The same goes for the linked page.
2007-11-28: cached again, the timestamp on the cached copy “27 Nov 2007 01:11:12 GMT” doesn’t match the last crawl on “2007-11-26 16:47:11 EST” (EST = GMT-5).
2007-12-07: recrawled, still deindexed, cached. Linked page recrawled, cached.
2007-12-17: recrawled, still deindexed (probably caused by near duplicate content on noarchive.php and other pages involved in this test), cached copy dated 2007-12-07. Cache of the linked page still dated 2007-11-21. I consider this case closed. Nofollow: doesn’t work as expected, Google doesn’t support this statement.

Noarchive:

robots.txt:
Noarchive: /repstuff/noarchive.php

Expected behavior:
Crawling, indexing, following links, but no “Cached” links on the SERPs and no access to cached copies from the toolbar.
Desired behavior:
Crawling, indexing, following links, but no “Cached” links on the SERPs and no access to cached copies from the toolbar.
Google’s robots.txt validator:
http://sebastians-pamphlets.com/repstuff/noarchive.php Allowed
Status:
See test page
Google’s crawler / indexer:
2007-11-21: crawled.
2007-11-23: indexed and cached.
2007-11-21: crawled a page linked only from noarchive.php.
2007-11-23: indexed and cached a page linked only from noarchive.php.
2007-11-26: recrawled, deindexed, no longer cached. The linked page was deindexed without recrawling.
2007-11-28: cached again, the timestamp on the cached copy “27 Nov 2007 01:11:19 GMT” doesn’t match the last crawl on “2007-11-26 16:47:18 EST” (EST = GMT-5).
2007-11-29: recrawled, cache not yet updated.
2007-12-07: recrawled. Linked page recrawled.
2007-12-08: recrawled.
2007-12-11: recrawled the linked page, which is cached but not indexed.
2007-12-12: recrawled.
2007-12-17: still indexed, cached copy dated 2007-12-08. I consider this case closed. Noarchive: doesn’t work as expected, actually it does nothing although according to the robots.txt validator that’s supported –or at least known and accepted– syntax.

(It looks like Google understands Nosnippet: too, but I didn’t test that.)

Nopreview:

robots.txt:
Nopreview: /repstuff/nopreview.pdf

Expected behavior:
None, unfortunately.
Desired behavior:
No “view as HTML” links on the SERPs. Neither “nosnippet” nor “noarchive” suppress these helpful preview links, which can be pretty annoying in some cases. See NOPREVIEW: The missing X-Robots-Tag.
Google’s robots.txt validator:
Line 33: Nopreview: /repstuff/nopreview.pdf Syntax not understood
http://sebastians-pamphlets.com/repstuff/nopreview.pdf Allowed
Status:
Crawler requests of nopreview.pdf are logged here.
Google’s crawler / indexer:
2007-11-21: crawled the nopreview-pdf and the log page nopreview.php.
2007-11-23: indexed and cached the log file nopreview.php.
[2007-11-23: I replaced the PDF document with a version carrying a hidden link to an HTML file, and resubmitted it via Google’s add-url page and a sitemap.]
2007-11-26: The old version of the PDF is cached as a “view-as-HTML” version without links (considering the PDF was a captured print job, that’s a pretty decent result), and appears on SERPs for a quoted search. The page linked from the PDF and the new PDF document were not yet crawled.
2007-12-02: PDF recrawled. Googlebot followed the hidden link in the PDF and crawled the linked page.
2007-12-03: “View as HTML” preview not yet updated, the linked page not yet indexed.
2007-12-04: PDF recrawled. The preview link reflects the content crawled on 12/02/2007. The page linked from the PDF is not yet indexed.
2007-12-07: PDF recrawled. Linked page recrawled.
2007-12-09: PDF recrawled.
2007-12-10: recrawled linked page.
2007-12-14: PDF recrawled. Cached copy of the linked page dated 2007-12-11.
2007-12-17: I consider this case closed. Neither Nopreview: nor Noarchive: (in robots.txt since 2007-12-04) are suitable to suppress the HTML preview of PDF files.

Noindex: Nofollow:

robots.txt:
Noindex: /repstuff/noindex-nofollow.php
Nofollow: /repstuff/noindex-nofollow.php

Expected behavior:
No crawling/indexing, invisible on SERPs.
Desired behavior:
No crawling/indexing, and no URL-only listings, ODP titles/descriptions and stuff like that on the SERPs. “Noindex:” in combination with “Nofollow:” is a paraphrased “Disallow:”.
Google’s robots.txt validator:
http://sebastians-pamphlets.com/repstuff/noindex-nofollow.php Blocked by line 35: Noindex: /repstuff/noindex-nofollow.php
Line 36: Nofollow: /repstuff/noindex-nofollow.php Syntax not understood
Status:
See test page
Google’s crawler / indexer:
2007-11-21: crawled.
2007-11-23: indexed and cached.
2007-11-21: crawled a page linked only from noindex-nofollow.php.
2007-11-23: indexed and cached a page linked only from noindex-nofollow.php.
2007-11-26: deindexed without recrawling, the same goes for the linked page.
2007-11-29: the cached copy retrieved on 11/21 reappeared.
2007-12-08: appeared under “URL restricted by robots.txt” in my GWC acct.
2007-12-17: Case closed, see Noindex: above.

Noindex: Follow:

robots.txt:
Noindex: /repstuff/noindex-follow.php
Follow: /repstuff/noindex-follow.php

Expected behavior:
No crawling/indexing, hence unfollowed links.
Desired behavior:
Crawling, following and indexing outgoing links, but no SERP listings.
Google’s robots.txt validator:
http://sebastians-pamphlets.com/repstuff/noindex-follow.php Blocked by line 38: Noindex: /repstuff/noindex-follow.php
Line 39: Follow: /repstuff/noindex-follow.php Syntax not understood
Status:
See test page
Google’s crawler / indexer:
2007-11-21: crawled.
2007-11-23: indexed and cached.
2007-11-21: crawled a page linked only from noindex-follow.php.
2007-11-23: indexed and cached a page linked only from noindex-follow.php.
2007-11-26: deindexed without recrawling, the same goes for the linked page.
2007-12-08: appeared under “URL restricted by robots.txt” in my GWC acct.
2007-12-17: Case closed, see Noindex: above. Google didn’t crawl respectively deindexed despite the Follow: directive.

Index: Nofollow:

robots.txt:
Index: /repstuff/index-nofollow.php
Nofollow: /repstuff/index-nofollow.php

Expected behavior:
Crawling/indexing, following links.
Desired behavior:
Crawling/indexing but ignoring outgoing links.
Google’s robots.txt validator:
Line 41: Index: /repstuff/index-nofollow.php Syntax not understood
Line 42: Nofollow: /repstuff/index-nofollow.php Syntax not understood
http://sebastians-pamphlets.com/repstuff/index-nofollow.php Allowed
Status:
See test page
Google’s crawler / indexer:
2007-11-21: crawled.
2007-11-23: indexed and cached.
2007-11-21: crawled a page linked only from from index-nofollow.php.
2007-11-23: indexed and cached a page linked only from from index-nofollow.php.
2007-11-26: recrawled and deindexed. The linked page was deindexed witout recrawling.
2007-11-28: cached again, the timestamp on the cached copy “27 Nov 2007 01:11:26 GMT” doesn’t match the last crawl on “2007-11-26 16:47:25 EST” (EST = GMT-5).
2007-12-02: recrawled, the cached copy has vanished.
2007-12-07: recrawled. Linked page recrawled.
2007-12-08: recrawled.
2007-12-09: recrawled.
2007-12-10: recrawled.
2007-12-17: cached under 2007-12-10, not indexed. Linked page not cached, not indexed. I consider this case closed. Google currently doesn’t support Index: nor Nofollow:.

(I didn’t test Noodp: and Unavaliable_after [RFC 850 formatted timestamp]:, although both directives would make sense in robots.txt too.)

2007-11-20:
Added the experimental statements to robots.txt.

2007-11-21:
Linked the test pages. Google crawled all of them, including the pages submitted via links on test pages.

2007-11-23:
Most (all but the PDF document) URLs appear on search result pages. If an outdated robots.txt cache falsely allowed crawling although the WC-validator said “Blocked”, the search results should disappear shortly after the next crawl. I’ve created a sitemap for all URLs above and submitted it. Although I’ve –for the sake of this experiment– cloaked text as well as links and put white links on white background, luckily there is no “we caught you black hat spammer” message in my Webmaster Console. Googlebot nicely followed the cloaked links and indexed everything.

2007-11-26:
Google recrawled a few pages (noarchive.php, index-nofollow.php and nofollow.php), then deindexed all of them. Only the PDF document is indexed, and Google created a “view-as-HTML” preview from this captured print job. It seems that Google crawled something from another host than “*.googlebot.com”, unfortunately I didn’t log all requests. Probably the deindexing was done by a sneaky bot discovering the simple cloaking. Since the linked URLs are out and 3rd party links to them can’t ruin the experiment any longer, I’ve stopped cloaking and show the same text/links to bots and users (actually, users see one more link but that should be fine with Google). There’s still no “thou shalt not cloak” message in my GWC account. Well, those pages are fairly new, perhaps not fully settled in the search index, so lets see what happens next.

2007-11-28
The PDF file as well as the three pages recrawled on 11/26/2007 21:45:00 GMT were reindexed, but the timestamp on the cached copies says “retrieved on 27 Nov 2007 01:15:00 GMT”. Maybe the date/time displayed on cached page copies doesn’t reflect Ms. Googlebot’s “fetched” timestamp, but the time the indexer pulled the page out of the centralized crawl results cache 3.5 hours after crawling.

It seems the “Noarchive:” directive doesn’t work, because noarchive.php was crawled and indexed twice providing a cached page copy. My “Nopreview:” creation isn’t supported either, but maybe Dan Crow’s team picks it up for a future update of their neat X-Robots-Tags (I hope so).

The noindex’ed pages (noindex.php, noindex-nofollow.php and noindex-follow.php) weren’t recrawled and remain deindexed. Interestingly, they don’t appear under “URLs blocked by robots.txt” in my GWC account. Provided the first crawling and indexing on 11/21/2007 was a “mistake” caused by a way too long cached robots.txt, and the second crawl on 11/26/2007 obeyed the “Noindex:” but ignored the (implicit) “Follow:”, it seems that indeed Google interprets “Noindex:” in robots.txt as “Disallow:”. If that is so and if it’s there to stay, they’re going to totally mess up the REP.

<rant> I mean, promoting a rel-nofollow microformat that –at least at launchtime– didn’t share its semantics with the REP’s meta tags nor the –later introduced– X-Robots-Tags was evil bad enough. Ok, meanwhile they’ve corrected this conspiracy flaw by altering the rel-nofollow semantics step by step until “nofollow” in the REL attribute actually means nofollow  and no longer pass no reputation, at least at Google. Other engines still handle rel-nofollow according to the initial and officially still binding standard, and a gazillion Webmasters are confused as hell. In other words only a few search geeks understand what rel-nofollow is all about, but Google jauntily penalizes the great unwashed for not complying to the incomprehensible. By the way, that’s why I code rel="nofollow crap". Standards should be clear and unambiguous. </rant>

If Google really would introduce a “Noindex:” directive in robots.txt that equals “Disallow:”, that would be totally evil. A few sites out there might have an erroneous “Noindex:” statement in their robots.txt that could mean “Disallow:”, and it’s nice that Google tries to do them a favor. Screwing the REP for the sole purpose of complying to syntax errors on the other hand makes no sense. “Noindex” means crawl it, follow its links, but don’t index it. Semantically “Noindex: Nofollow:” equals “Disallow:”, but a “Noindex:” alone implies a “Follow:”, hence crawling is not only allowed but required.

I really hope that we watch an experiment in its early stage, and that Google will do the right thing eventually. Allowing the REP’s page specific crawler directives in robots.txt is a fucking brilliant move, because technically challenged publishers can’t handle the HTTP header’s X-Robots-Tag, and applying those directives to groups of URIs is a great method to steer crawling and indexing not only with static sites.

Dear Google engineers, please consider the nopreview directive too, and implement (no)index, (no)follow, noarchive, nosnippet, noodp/noydir and unavailable_after with the REP’s meaning. And while you’re at it, I want block level instructions in robots.txt too. For example
Area: /products/ DIV.hMenu,TD#bNav,SPAN.inherited "noindex,nofollow"

could instruct crawlers to ignore duplicated properties in product descriptions and the horizontal menu as well as the navigation elements in a table cell with the DOM-ID “bNav” at the very bottom of all pages in /products/,
Area: / A.advertising REL="nofollow"

could condomize all links with the class name “advertising”, and so on.

2007-11-29
The pages linked from the test pages still don’t come up in search results, noarchive.php was recrawled and remains cached, the cached copy of noindex-nofollow.php retrieved on 11/21/2007 reappeared (probably a DC roller coaster issue).

2007-11-30
Three URLs remain indexed: nopreview.pdf, noarchive.php and noindex-nofollow.php. The cached copies show the content crawled on Nov/21/2007. Everything else is deindexed. That’s not to stay (index roller coaster).
As a side note: the URL from my first noindex-robots.txt test appeared in my GWC account under “URLs restricted by robots.txt (Nov/27/2007)”, three days after the unsuccessful crawl.

2007-12-02
A few pages were recrawled, Googlebot followed the hidden link in the PDF file.

2007-12-03
In my GWC crawl stats noindex-nofollow.php appeared under “URLs restricted by robots.txt”, but it’s still indexed.

2007-12-04
The preview (cache) of nopreview.pdf was updated. Since obviously Nopreview: doesn’t work, I’ve added
Noarchive: /repstuff/nopreview.pdf

to my robots.txt. Lets see whether Google removes the cache respectively the HTML preview or not.

2007-12-06
Shortly after the change in robots.txt (Noarchive: /repstuff/nopreview.pdf) Googlebot recrawled the PDF file on 12/04/2007. Today it’s still cached, the HTML preview is still available and linked from SERPs.

2007-12-07
Googlebot has recrawled a few pages. Everything except noarchive.php and nopreview.pdf is deindexed.

2007-12-17
I consider the test closed, but I’ll keep the test pages up so that you can monitor crawling and indexing yourself. Noindex: is the only directive that somewhat works, but it’s implemented completely wrong and is not acceptable in its current shape.

Interestingly the sitemaps report in my GWC account says that 9 pages from 9 submitted URLs were indexed. Obviously “indexed” means something like “crawled at least once, perhaps indexed, maybe not, so if you want to know that definitively then get your lazy butt to check the SERPs yourself”. How expensive would it be to tell something like “Total URLs in sitemap: 9 | Indexed URLs in sitemap: 2″?



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Microsoft funding bankrupt Live Search experiment with porn spam

If only this headline would be linkbait … of course it’s not sarcastic.

M$ PORN CASHRumors are out that Microsoft will launch a porn affiliate programm soon. The top secret code name for this project is “pornbucks”, but analysts say that it will be launched as “M$ SMUT CASH” next year or so.

Since Microsoft just can’t ship anything in time, and the usual delays aren’t communicated internally, their search dept. began to promote it to Webmasters this summer.

Surprisingly, Webmasters across the globe weren’t that excited to find promotinal messages from Live Search in their log files, so a somewhat confused MSN dude posted a lame excuse to a large Webmaster forum.

Meanwhile we found out that Microsoft Live Search does not only target the adult entertainment industry, they’re testing the waters with other money terms like travel or pharmaceutic products too.

Anytime soon the Live Search menu bar will be updated to something like this:
Live Search Porn Spam Menu

Here is the sad –but true– story of a search engine’s downfall.

A few months ago Microsoft Live Search discovered that x-rated referrer spam is a must-have technique in a sneaky smut peddlar’s marketing toolbox.

Since August 2007 a bogus Web robot follows Microsoft’s search engine crawler “MSNbot” to spam the referrer logs of all Web sites out there with URLs pointing to MSN search result pages featuring porn.

Read your referrer logs and you’ll find spam from Microsoft too, but perhaps they peeve you with viagra spam, offer you unwanted but cheap payday loans, or try to enlarge your penis. Of course they know every trick in the book on spam, so check for harmless catchwords too. Here is an example URL:
http://search.live.com/results.aspx?q= spammy-keyword &mrt=en-us&FORM=LIVSOP

Microsoft’s spam bot not only leaves bogus URLs in log files, hoping that Webmasters will click them on their referrer stats pages and maybe sign up for something like “M$ Porn Bucks” or so. It downloads and renders even adverts powered by their rival Google, lowering their CTR; obviously to make programs like AdSense less attractive im comparison with Microsoft’s own ads (sorry, no link love from here).

Let’s look at Microsoft’s misleading statement:

The traffic you are seeing is part of a quality check we run on selected pages. While we work on addressing your conerns, we would request that you do not actively block the IP addreses used by this quality check; blocking these IP addresses could prevent your site from being included in the Live Search index.

  • That’s not traffic, that’s bot activity: These hits come within seconds of being indexed by MSNBot. The pattern is like this: the page is requested by MSNBot (which is authenticated, so it’s genuine) and within a few seconds, the very same page is requested with a live.com search result URL as referer by the MSN spam bot faking a human visitor.
  • If that’s really a quality check to detect cloaking, that’s more than just lame. The IP addresses don’t change, the bogus bot uses a static user agent name, and there are other footprints which allow every cloaking script out there to serve this sneaky bot the exact same spider fodder that MSNbot got seconds before. This flawed technique might catch poor man’s cloaking every once in a while, but it can’t fool savvy search marketers.
  • The FUD “could prevent your site from being included in the Live Search index” is laughable, because in most niches MSN search traffic is not existent.

All major search engines, including MSN, promise that they obey the robots exclusion standard. Obeying robots.txt is the holy grail of search engine crawling. A search engine that ignores robots.txt and other normed crawler directives cannot be trusted. The crappy MSN bot not even bothers to read robots.txt, so there’s no chance to block it with standardized methods. Only IP blocking can keep it out, but then it still seems to download ads from Google’s AdSense servers by executing the JavaScript code that the MSN crawler gathered before (not obeying Google’s AdSense robots.txt as well).

This unethical spam bot downloading all images, external CSS and JS files, and whatnot also burns bandwidth. That’s plain theft.

Since this method cannot detect (most) cloaking, and the so called “search quality control bot” doesn’t stop visiting sites which obviously do not cloak, it is a sneaky marketing tool. Whether or not Microsoft Live Search tries to promote cyberspace porn and on-line viagra shops plays no role. Even spamming with safe-at-work keywords is evil. Do these assclowns really believe that such unethical activities will increase the usage of their tiny and pretty unpopular search engine? Of course they do, otherwise they would have shutted down the spam bot months ago.

Dear reader, please tell me: what do you think of a search engine that steals (bandwidth and AdSense revenue), lies, spams away, and is not clever enough to stop their criminal activities when they’re caught?

Recently a Live Search rep whined in an interview because so many robots.txt files out there block their crawler:

One thing that we noticed for example while mining our logs is that there are still a fair number of sites that specifically only allow Googlebot and do not allow MSNBot.

There’s a suitable answer, though. Update your robots.txt:

User-agent: MSNbot
Disallow: /



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Q&A: An undocumented robots.txt crawler directive from Google

What's the fuss about noindex in Google's robots.txt?Blogging should be fun every now and then. Today I don’t tell you anything new about Google’s secret experiments with the robots exclusion protocol. I ask you instead, because I’m sure you know your stuff. Unfortunately, the Q&A on undocumented robots.txt syntax from Google’s labs utilizes JavaScript, so perhaps it looks somewhat weird in your feed reader.

Q: Please look at this robots.txt file and figure out why it’s worth a Q&A with you, my dear reader:


User-Agent: *
Disallow: /
Noindex: /

Ok, click here to show the first hint.

I know, this one was a breeze, so here comes your challenge.
Q: Which crawler directive used in the robots.txt above was introduced 1996 in the Robots Exclusion Protocol (REP), but was not defined in its very first version from 1994?

Ok, click here to show the second hint.

Congrats, you are smart. I’m sure you don’t need to lookup the next answers.
Q: Which major search engine has a team permanently working on REP extensions and releases those quite frequently, and who is the engineer in charge?

Ok, click here to show the third hint.

Exactly. Now we’ve gathered all the pieces of this robots.txt puzzle.
Q: Could you please summarize your cognitions and conclusions?

Ok, click here to show the fourth hint.

Thank you, dear reader! Now lets see what we can dig out. If the appearance of a “Noindex:” directive in robots.txt is an experiment, it would make sense that Ms. Googlebot understands and obeys it. Unfortunetely, I sold all the source code I’ve stolen from Google and didn’t keep a copy for myself, so I need to speculate a little.

Last time I looked, Google’s cool robots.txt validator emulated crawler behavior, that means that the crawlers understood syntax the validator didn’t handle correctly. Maybe this was changed in the meantime, perhaps the validator pulls its code from the “real thing” now, or at least the “Noindex:” experiment may have found its way into the validator’s portfolio. So I thought that testing the newish robots.txt statement “Noindex:” in the Webmaster Console is worth a try. And yes, it told me that Googlebot understands this command, and interprets it as “Disallow:”.
Blocked by line 27: Noindex: /noindex/

Since validation is no proof of crawler behavior, I’ve set up a page “blocked” with a “Noindex:” directive in robots.txt and linked it in my sidebar. The noindex statement was in place long enough before I’ve uploaded and linked the spider trap, so that the engines shouldn’t use a cached robots.txt when they follow my links. My test is public, feel free to check out my robots.txt as well as the crawler log.

While I’m waiting for the expected growth of my noindex crawler log, I’m speculating. Why the heck would Google use a new robots.txt directive which behaves like the good old Disallow: statement? Makes no sense to me.

Lets not forget that this mysterious noindex statement was discovered in the robots.txt of Google’s ad server, not in the better known and closely watched robots.txt of google.com. Google is not the only search engine trying to better understand client sided code. None of the major engines should be interested in crawling ads for ranking purposes. The MSN/LiveSearch referrer spam fiasco demonstrates that search engine bots can fetch and render Google ads outputted in iFrames on pagead2.googlesyndication.com.

Since nobody supports Google’s X-Robots-Tag (sending “noindex” and other REP directives in the HTTP header) until today, maybe the engines have a silent deal that content marked with “Noindex:” in robots.txt shouldn’t be indexed. Microsoft’s bogus spam bot which doesn’t bother with robots.txt because it somewhat hapless tries to emulate a human surfer is not considered a crawler, it’s existence just proves that “software shop” is not a valid label for M$.

This theory has a few weak points, but it could point to something. If noindex in robots.txt really prevents from indexing of contents crawled by accident, or non-HTML contents that can’t supply robots meta tags, that would be a very useful addition to the robots exclusion protocol. Of course we’d then need Noarchive:, Nofollow: and Nopreview: too, probably more but I’m not really in a greedy mood today.

Back to my crawler trap. Refreshing the log reveals that 30 minutes after spreading links pointing to it, Googlebot has fetched the page. That seems to prove that the Noindex: statement doesn’t prevent from crawling, regardless the false (?) information handed out by Google’s robots.txt validator.

(Or didn’t I give Ms. Googlebot enough time to refetch my robots.txt? Dunno. The robots.txt copy in my Google Webmaster Console still doesn’t show the Noindex: statement, but I doubt that’s the version Googlebot uses because according to the last-downloaded timestamp in GWC the robots.txt has been changed at the time of the download. Never mind. If I was way too impatient, I still can test whether a newly discovered noindex directive in robots.txt actually deindexes stuff or not.)

On with the show. The next interesting question is: Will the crawler trap page make it in Google’s search index? Without the possibly non-effective noindex directive a few hundred links should be able to accomplish that. Alas, a quoted search query delivers zilch so far.

Of course I’ve asked Google for more information, but didn’t receive a conclusive answer so far. While waiting for an official statement, I take a break from live blogging this quick research in favor of terrorizing a few folks with respectless blog comments. Stay tuned. Be right back.


Well, meanwhile I had dinner, the kids fell asleep –hopefully until tomorrow morning–, but nothing else happened. A very nice and friendly Googler tries to find out what the noindex in robots.txt fuss is all about, thanks and I can’t wait! However, I suspect the info is either forgotten or deeply buried in some well secured top secret code libraries, hence I’ll push the red button soon.


Thanks to Google’s great Webmaster Central team, especially Susan, I learned that I was flogging a dead horse. Here is Google’s take on Noindex in robots.txt:

As stated in my previous note, I wasn’t aware that we recognized any directives other than Allow/Disallow/Sitemap, so I did some asking around.

Unfortunately, I don’t have an answer that I can currently give you. […] I can’t contribute any clarifications right now.

Thank you Susan!

Update: John Müller from Google has just confirmed that their crawler understands the Noindex: syntax, but it’s not yet set in stone.



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Act out your sophisticated affiliate link paranoia

GOOD: paranoid affiliate linkMy recent posts on managing affiliate links and nofollow cloaking paid links led to so many reactions from my readers that I thought explaining possible protection levels could make sense. Google’s request to condomize affiliate links is a bit, well, thin when it comes to technical tips and tricks:

Links purchased for advertising should be designated as such. This can be done in several ways, such as:
* Adding a rel=”nofollow” attribute to the <a> tag
* Redirecting the links to an intermediate page that is blocked from search engines with a robots.txt file

Also, Google doesn’t define paid links that clearly, so try this paid link definition instead before your read on. Here is my linking guide for the paranoid affiliate marketer.

Google recommends hiding of any content provided by affiliate programs from their crawlers. That means not only links and banner ads, so think about tactics to hide content pulled from a merchants data feed too. Linked graphics along with text links, testimonials and whatnot copied from an affiliate program’s sales tools page count as duplicate content (snippet) in its worst occurance.

Pasting code copied from a merchant’s site into a page’s or template’s HTML is not exactly a smart way to put ads. Those ads aren’t manageable nor trackable, and when anything must be changed, editing tons of files is a royal PITA. Even when you’re just running a few ads on your blog, a simple ad management script allows flexible administration of your adverts.

There are tons of such scripts out there, so I don’t post a complete solution, but just the code which saves your ass when a search engine hating your ads and paid links comes by. To keep it simple and stupid my code snippets are mostly taken from this blog, so when you’ve a WordPress blog you can adapt them with ease.

Cover your ass with a linking policy

Googlers as well as hired guns do review Web sites for violations of Google’s guidelines, also competitors might be in the mood to turn you in with a spam report or paid links report. A (prominently linked) full disclosure of your linking attitude can help to pass a human review by search engine staff. By the way, having a policy for dofollowed blog comments is also a good idea.

Since crawler directives like link condoms are for search engines (only), and those pay attention to your source code and hints addressing search engines like robots.txt, you should leave a note there too, look into the source of this page for an example. View sample HTML comment.

Block crawlers from your propaganda scripts

Put all your stuff related to advertising (scripts, images, movies…) in a subdirectory and disallow search engine crawling in your /robots.txt file:
User-agent: *
Disallow: /propaganda/

Of course you’ll use an innocuous name like “gnisitrevda” for this folder, which lacks a default document and can’t get browsed because you’ve a
Options -Indexes

statement in your .htaccess file. (Watch out, Google knows what “gnisitrevda” means, so be creative or cryptic.)

Crawlers sent out by major search engines do respect robots.txt, hence it’s guaranteed that regular spiders don’t fetch it. As long as you don’t cheat too much, you’re not haunted by those legendary anti-webspam bots sneakily accessing your site via AOL proxies or Level3 IPs. A robots.txt block doesn’t prevent you from surfing search engine staff, but I don’t tell you things you’d better hide from Matt’s gang.

Detect search engine crawlers

Basically there are three common methods to detect requests by search engine crawlers.

  1. Testing the user agent name (HTTP_USER_AGENT) for strings like “Googlebot”, “Slurp”, “MSNbot” or so which identify crawlers. That’s easy to spoof, for example PrefBar for FireFox lets you choose from a list of user agents.
  2. Checking the user agent name, and only when it indicates a crawler, verifying the requestor’s IP address with a reverse lookup, respectively against a cache of verified crawler IP addresses and host names.
  3. Maintaining a list of all search engine crawler IP addresses known to man, checking the requestor’s IP (REMOTE_ADDR) against this list. (That alone isn’t bullet-proof, but I’m not going to write a tutorial on industrial-strength cloaking IP delivery, I leave that to the real experts.)

For our purposes we use method 1) and 2). When it comes to outputting ads or other paid links, checking the user agent is save enough. Also, this allows your business partners to evaluate your linkage using a crawler as user agent name. Some affiliate programs won’t activate your account without testing your links. When crawlers try to follow affiliate links on the other hand, you need to verify their IP addresses for two reasons. First, you should be able to upsell spoofing users too. Second, if you allow crawlers to follow your affiliate links, this may have impact on the merchants’ search engine rankings, and that’s evil in Google’s eyes.

We use two PHP functions to detect search engine crawlers. checkCrawlerUA() returns TRUE and sets an expected crawler host name, if the user agent name identifies a major search engine’s spider, or FALSE otherwise. checkCrawlerIP($string) verifies the requestor’s IP address and returns TRUE if the user agent is indeed a crawler, or FALSE otherwise. checkCrawlerIP() does a primitive caching in a flat file, so that once a crawler was verified on its very first content request, it can be detected from this cache to avoid pretty slow DNS lookups. The input parameter is any string which will make it into the log file. checkCrawlerIP() does not verify an IP address if the user agent string doesn’t match a crawler name.

View|hide PHP code. (If you’ve disabled JavaScript you can’t grab the PHP source code!)

Grab and implement the PHP source, then you can code statements like
$isSpider = checkCrawlerUA ();
...
if ($isSpider) {
$relAttribute = " rel=\"nofollow\" ";
}
...
$affLink = "<a href=\"$affUrl\" $relAttribute>call for action</a>";

or
$isSpider = checkCrawlerIP ($sponsorUrl);
...
if ($isSpider) {
// don't redirect to the sponsor, return a 403 or 410 instead
}

More on that later.

Don’t deliver your advertising to search engine crawlers

It’s possible to serve totally clean pages to crawlers, that is without any advertising, not even JavaScript ads like AdSense’s script calls. Whether you go that far or not depends on the grade of your paranoia. Suppressing ads on a (thin|sheer) affiliate site can make sense. Bear in mind that hiding all promotional links and related content can’t guarantee indexing, because Google doesn’t index shitloads of templated pages witch hide duplicate content as well as ads from crawling, without carrying a single piece of somewhat compelling content.

Here is how you could output a totally uncrawlable banner ad:
...
$isSpider = checkCrawlerIP ($PHP_SELF);
...
print "<div class=\"css-class-sidebar robots-nocontent\">";
// output RSS buttons or so
if (!$isSpider) {
print "<script type=\"text/javascript\" src=\"http://sebastians-pamphlets.com/propaganda/output.js.php? adName=seobook&adServed=banner\"></script>";
...
}
...
print "</div>\n";
...

Lets look at the code above. First we detect crawlers “without doubt” (well, in some rare cases it can still happen that a suspected Yahoo crawler comes from a non-’.crawl.yahoo.net’ host but another IP owned by Yahoo, Inktomi, Altavista or AllTheWeb/FAST, and I’ve seen similar reports of such misbehavior for other engines too, but that might have been employees surfing with a crawler-UA).

Currently the robots-nocontent  class name in the DIV is not supported by Google, MSN and Ask, but it tells Yahoo that everything in this DIV shall not be used for ranking purposes. That doesn’t conflict with class names used with your CSS, because each X/HTML element can have an unlimited list of space delimited class names. Like Google’s section targeting that’s a crappy crawler directive, though. However, it doesn’t hurt to make use of this Yahoo feature with all sorts of screen real estate that is not relevant for search engine ranking algos, for example RSS links (use autodetect and pings to submit), “buy now”/”view basket” links or references to TOS pages and alike, templated text like terms of delivery (but not the street address provided for local search) … and of course ads.

Ads aren’t outputted when a crawler requests a page. Of course that’s cloaking, but unless the united search engine geeks come out with a standardized procedure to handle code and contents which aren’t relevant for indexing that’s not deceitful cloaking in my opinion. Interestingly, in many cases cloaking is the last weapon in a webmaster’s arsenal that s/he can fire up to comply to search engine rules when everything else fails, because the crawlers behave more and more like browsers.

Delivering user specific contents in general is fine with the engines, for example geo targeting, profile/logout links, or buddy lists shown to registered users only and stuff like that, aren’t penalized. Since Web robots can’t pull out the plastic, there’s no reason to serve them ads just to waste bandwidth. In some cases search engines even require cloaking, for example to prevent their crawlers from fetching URLs with tracking variables and unavoidable duplicate content. (Example from Google: “Allow search bots to crawl your sites without session IDs or arguments that track their path through the site” is a call for search engine friendly URL cloaking.)

Is hiding ads from crawlers “safe with Google” or not?

BAD: uncloaked affiliate linkCloaking ads away is a double edged sword from a search engine’s perspective. Way too strictly interpreted that’s against the cloaking rule which states “don’t show crawlers other content than humans”, and search engines like to be aware of advertising in order to rank estimated user experiences algorithmically. On the other hand they provide us with mechanisms (Google’s section targeting or Yahoo’s robots-nocontent class name) to disable such page areas for ranking purposes, and they code their own ads in a way that crawlers don’t count them as on-the-page contents.

Although Google says that AdSense text link ads are content too, they ignore their textual contents in ranking algos. Actually, their crawlers and indexers don’t render them, they just notice the number of script calls and their placement (at least if above the fold) to identify MFA pages. In general, they ignore ads as well as other content outputted with client sided scripts or hybrid technologies like AJAX, at least when it comes to rankings.

Since in theory the contents of JavaScript ads aren’t considered food for rankings, cloaking them completely away (supressing the JS code when a crawler fetches the page) can’t be wrong. Of course these script calls as well as on-page JS code are a ranking factors. Google possibly counts ads, maybe calculates even ratios like screen size used for advertising etc. vs. space used for content presentation to determine whether a particular page provides a good surfing experience for their users or not, but they can’t argue seriously that hiding such tiny signals –which they use for the sole purposes of possible downranks– is against their guidelines.

For ages search engines reps used to encourage webmasters to obfuscate all sorts of stuff they want to hide from crawlers, like commercial links or redundant snippets, by linking/outputting with JavaScript instead of crawlable X/HTML code. Just because their crawlers evolve, that doesn’t mean that they can take back this advice. All this JS stuff is out there, on gazillions of sites, often on pages which will never be edited again.

Dear search engines, if it does not count, then you cannot demand to keep it crawlable. Well, a few super mega white hat trolls might disagree, and depending on the implementation on individual sites maybe hiding ads isn’t totally riskless in any case, so decide yourself. I just cloak machine-readable disclosures because crawler directives are not for humans, but don’t try to hide the fact that I run ads on this blog.

Usually I don’t argue with fair vs. unfair, because we talk about war business here, what means that everything goes. However, Google does everything to talk the whole Internet into obfuscating disclosing ads with link condoms of any kind, and they take a lot of flak for such campaigns, hence I doubt they would cry foul today when webmasters hide both client sided as well as server sided delivery of advertising from their crawlers. Penalizing for delivery of sheer contents would be unfair. ;) (Of course that’s stuff for a great debate. If Google decides that hiding ads from spiders is evil, they will react and don’t care about bad press. So please don’t take my opinion as professional advice. I might change my mind tomorrow, because actually I can imagine why Google might raise their eyebrows over such statements.)

Outputting ads with JavaScript, preferably in iFrames

Delivering adverts with JavaScript does not mean that one can’t use server sided scripting to adjust them dynamically. With content management systems it’s not always possible to use PHP or so. In WordPress for example, PHP is executable in templates, posts and pages (requires a plugin), but not in sidebar widgets. A piece of JavaScript on the other hand works (nearly) everywhere, as long as it doesn’t come with single quotes (WordPress escapes them for storage in its MySQL database, and then fails to output them properly, that is single quotes are converted to fancy symbols which break eval’ing the PHP code).

Lets see how that works. Here is a banner ad created with a PHP script and delivered via JavaScript:

And here is the JS call of the PHP script:
<script type="text/javascript" src="http://sebastians-pamphlets.com/propaganda/output.js.php? adName=seobook&adServed=banner"></script>

The PHP script /propaganda/output.js.php evaluates the query string to pull the requested ad’s components. In case it’s expired (e.g. promotions of conferences, affiliate program went belly up or so) it looks for an alternative (there are tons of neat ways to deliver different ads dependent on the requestor’s location and whatnot, but that’s not the point here, hence the lack of more examples). Then it checks whether the requestor is a crawler. If the user agent indicates a spider, it adds rel=nofollow to the ad’s links. Once the HTML code is ready, it outputs a JavaScript statement:
document.write(‘<a href="http://sebastians-pamphlets.com/propaganda/router.php? adName=seobook&adServed=banner" title="DOWNLOAD THE BOOK ON SEO!"><img src="http://sebastians-pamphlets.com/propaganda/seobook/468-60.gif" width="468" height="60" border="0" alt="The only current book on SEO" title="The only current book on SEO" /></a>’);
which the browser executes within the script tags (replace single quotes in the HTML code with double quotes). A static ad for surfers using ancient browsers goes into the noscript tag.

Matt Cutts said that JavaScript links don’t prevent Googlebot from crawling, but that those links don’t count for rankings (not long ago I read a more recent quote from Matt where he stated that this is future-proof, but I can’t find the link right now). We know that Google can interpret internal and external JavaScript code, as long as it’s fetchable by crawlers, so I wouldn’t say that delivering advertising with client sided technologies like JavaScript or Flash is a bullet-proof procedure to hide ads from Google, and the same goes for other major engines. That’s why I use rel-nofollow –on crawler requests– even in JS ads.

Change your user agent name to Googlebot or so, install Matt’s show nofollow hack or something similar, and you’ll see that the affiliate-URL gets nofollow’ed for crawlers. The dotted border in firebrick is extremely ugly, detecting condomized links this way is pretty popular, and I want to serve nice looking pages, thus I really can’t offend my readers with nofollow’ed links (although I don’t care about crawler spoofing, actually that’s a good procedure to let advertisers check out my linking attitude).

We look at the affiliate URL from the code above later on, first lets discuss other ways to make ads more search engine friendly. Search engines don’t count pages displayed in iFrames as on-page contents, especially not when the iFrame’s content is hosted on another domain. Here is an example straight from the horse’s mouth:
<iframe name="google_ads_frame" src="http://pagead2.googlesyndication.com/pagead/ads? very-long-and-ugly-query-string" marginwidth="0" marginheight="0" vspace="0" hspace="0" allowtransparency="true" frameborder="0" height="90" scrolling="no" width="728"></iframe>
In a noframes tag we could put a static ad for surfers using browsers which don’t support frames/iFrames.

If for some reasons you don’t want to detect crawlers, or it makes sound sense to hide ads from other Web robots too, you could encode your JavaScript ads. This way you deliver totally and utterly useless gibberish to anybody, and just browsers requesting a page will render the ads. Example: any sort of text or html block that you would like to encrypt and hide from snoops, scrapers, parasites, or bots, can be run through Michael’s Full Text/HTML Obfuscator Tool (hat tip to Donna).

Always redirect to affiliate URLs

There’s absolutely no point in using ugly affiliate URLs on your pages. Actually, that’s the last thing you want to do for various reasons.

  • For example, affiliate URLs as well as source codes can change, and you don’t want to edit tons of pages if that happens.
  • When an affiliate program doesn’t work for you, goes belly up or bans you, you need to route all clicks to another destination when the shit hits the fan. In an ideal world, you’d replace outdated ads completely with one mouse click or so.
  • Tracking ad clicks is no fun when you need to pull your stats from various sites, all of them in another time zone, using their own –often confusing– layouts, providing different views on your data, and delivering program specific interpretations of impressions or click throughs. Also, if you don’t track your outgoing traffic, some sponsors will cheat and you can’t prove your gut feelings.
  • Scrapers can steal revenue by replacing affiliate codes in URLs, but may overlook hard coded absolute URLs which don’t smell like affiliate URLs.

When you replace all affiliate URLs with the URL of a smart redirect script on one of your domains, you can really manage your affiliate links. There are many more good reasons for utilizing ad-servers, for example smart search engines which might think that your advertising is overwhelming.

Affiliate links provide great footprints. Unique URL parts respectively query string variable names gathered by Google from all affiliate programs out there are one clear signal they use to identify affiliate links. The values identify the single affiliate marketer. Google loves to identify networks of ((thin) affiliate) sites by affiliate IDs. That does not mean that Google detects each and every affiliate link at the time of the very first fetch by Ms. Googlebot and the possibly following indexing. Processes identifying pages with (many) affiliate links and sites plastered with ads instead of unique contents can run afterwords, utilizing a well indexed database of links and linking patterns, reporting the findings to the search index respectively delivering minus points to the query engine. Also, that doesn’t mean that affiliate URLs are the one and only trackable footmark Google relies on. But that’s one trackable footprint you can avoid to some degree.

If the redirect-script’s location is on the same server (in fact it’s not thanks to symlinks) and not named “adserver” or so, chances are that a heuristic check won’t identify the link’s intent as promotional. Of course statistical methods can discover your affiliate links by analyzing patterns, but those might be similar to patterns which have nothing to do with advertising, for example click tracking of editorial votes, links to contact pages which aren’t crawlable with paramaters, or similar “legit” stuff. However, you can’t fool smart algos forever, but if you’ve a good reason to hide ads every little might help. Of course, providing lots of great contents countervails lots of ads (from a search engine’s point of view, and users might agree on this).

Besides all these (pseudo) black hat thoughts and reasoning, there is a way more important advantage of redirecting links to sponsors: blocking crawlers. Yup, search engine crawlers must not follow affiliate URLs, because it doesn’t benefit you (usually). Actually, every affiliate link is a useless PageRank leak. Why should you boost the merchants search engine rankings? Better take care of your own rankings by hiding such outgoing links from crawlers, and stopping crawlers before they spot the redirect, if they by accident found an affiliate link without link condom.

The behavior of an adserver URL masking an affiliate link

Lets look at the redirect-script’s URL from my code example above:
/propaganda/router.php?adName=seobook&adServed=banner
On request of router.php the $adName variable identifies the affiliate link, $adServed tells which sort/type/variation of ad was clicked, and all that gets stored with a timestamp under title and URL of the page carrying the advert.

Now that we’ve covered the statistical requirements, router.php calls the checkCrawlerIP() function setting $isSpider to TRUE only when both the user agent as well as the host name of the requestor’s IP address identify a search engine crawler, and a reverse DNS lookup equals the requestor’s IP addy.

If the requestor is not a verified crawler, router.php does a 307 redirect to the sponsor’s landing page:
$sponsorUrl = "http://www.seobook.com/262.html";
$requestProtocol = $_SERVER["SERVER_PROTOCOL"];
$protocolArr = explode("/",$requestProtocol);
$protocolName = trim($protocolArr[0]);
$protocolVersion = trim($protocolArr[1]);
if (stristr($protocolName,"HTTP")
&& strtolower($protocolVersion) > "1.0" ) {
$httpStatusCode = 307;
}
else {
$httpStatusCode = 302;
}
$httpStatusLine = "$requestProtocol $httpStatusCode Temporary Redirect";
@header($httpStatusLine, TRUE, $httpStatusCode);
@header("Location: $sponsorUrl");
exit;

A 307 redirect avoids caching issues, because 307 redirects must not be cached by the user agent. That means that changes of sponsor URLs take effect immediately, even when the user agent has cached the destination page from a previous redirect. If the request came in via HTTP/1.0, we must perform a 302 redirect, because the 307 response code was introduced with HTTP/1.1 and some older user agents might not be able to handle 307 redirects properly. User agents can cache the locations provided by 302 redirects, so possibly when they run into a page known to redirect, they might request the outdated location. For obvious reasons we can’t use the 301 response code, because 301 redirects are always cachable. (More information on HTTP redirects.)

If the requestor is a major search engine’s crawler, we perform the most brutal bounce back known to man:
if ($isSpider) {
@header("HTTP/1.1 403 Sorry Crawlers Not Allowed", TRUE, 403);
@header("X-Robots-Tag: nofollow,noindex,noarchive");
exit;
}

The 403 response code translates to “kiss my ass and get the fuck outta here”. The X-Robots-Tag in the HTTP header instructs crawlers that the requested URL must not be indexed, doesn’t provide links the poor beast could follow, and must not be publically cached by search engines. In other words the HTTP header tells the search engine “forget this URL, don’t request it again”. Of course we could use the 410 response code instead, which tells the requestor that a resource is irrevocably dead, gone, vanished, non-existent, and further requests are forbidden. Both the 403-Forbidden response as well as the 410-Gone return code prevent you from URL-only listings on the SERPs (once the URL was crawled). Personally, I prefer the 403 response, because it perfectly and unmistakably expresses my opinion on this sort of search engine guidelines, although currently nobody except Google understands or supports X-Robots-Tags in HTTP headers.

If you don’t use URLs provided by affiliate programs, your affiliate links can never influence search engine rankings, hence the engines are happy because you did their job so obedient. Not that they otherwise would count (most of) your affiliate links for rankings, but forcing you to castrate your links yourself makes their life much easier, and you don’t need to live in fear of penalties.

NICE: prospering affiliate linkBefore you output a page carrying ads, paid links, or other selfish links with commercial intent, check if the requestor is a search engine crawler, and act accordingly.

Don’t deliver different (editorial) contents to users and crawlers, but also don’t serve ads to crawlers. They just don’t buy your eBook or whatever you sell, unless a search engine sends out Web robots with credit cards able to understand Ajax, respectively authorized to fill out and submit Web forms.

Your ads look plain ugly with dotted borders in firebrick, hence don’t apply rel=”nofollow” to links when the requestor is not a search engine crawler. The engines are happy with machine-readable disclosures, and you can discuss everything else with the FTC yourself.

No nay never use links or content provided by affiliate programs on your pages. Encapsulate this kind of content delivery in AdServers.

Do not allow search engine crawlers to follow your affiliate links, paid links, nor other disliked votes as per search engine guidelines. Of course condomizing such links is not your responsibility, but getting penalized for not doing Google’s job is not exactly funny.

I admit that some of the stuff above is for extremely paranoid folks only, but knowing how to be paranoid might prevent you from making silly mistakes. Just because you believe that you’re not paranoid, that does not mean Google will not chase you down. You really don’t need to be a so called black hat to displease Google. Not knowing respectively not understanding Google’s 12 commandments doesn’t prevent you from being spanked for sins you’ve never heard of. If you’re keen on Google’s nicely targeted traffic, better play by Google’s rules, leastwise on creawler requests.

Feel free to contribute your tips and tricks in the comments.



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A pragmatic defence against Google’s anti paid links campaign

Google’s recent shot across the bows of a gazillion sites handling paid links, advertising, or internal cross links not compliant to Google’s imagination of a natural link is a call for action. Google’s message is clear: “condomize your commercial links or suffer” (from deducted toolbar PageRank, links without the ability to pass real PageRank and relevancy signals, or perhaps even penalties).

Paid links: good versus evilOf course that’s somewhat evil, because applying nofollow values to all sorts of links is not exactly a natural thing to do; visitors don’t care about invisible link attributes and sometimes they’re even pissed when they get redirected to an URL not displayed in their status bar. Also, this requirement forces Webmasters to invest enormous efforts in code maintenance for the sole purpose of satisfying search engines. The argument “if Google doesn’t like these links, then they can discount them in their system, without bothering us” has its merits, but unfortunately that’s not the way Google’s cookie crumbles for various reasons. Hence lets develop a pragmatic procedure to handle those links.

The problem

Google thinks that uncondomized paid links as well as commercial links to sponsors or affiliated entities aren’t natural, because the terms “sponsor|pay for review|advertising|my other site|sign-up|…” and “editorial vote” are not compatible in the sense of Google’s guidelines. This view at the Web’s linkage is pretty black vs. white.

Either you link out because a sponsor bought ads, or you don’t sell ads and link out for free because you honestly think your visitors will like a page. Links to sponsors without condom are black, links to sites you like and which you don’t label “sponsor” are white.

There’s nothing in between, respectively gray areas like links to hand picked sponsors on a page with a gazillion of links count as black. Google doesn’t care whether or not your clean links actually pass a reasonable amount of PageRank to link destinations which buy ad space too, the sole possibility that those links could  influence search results is enough to qualify you as sort of a link seller.

The same goes for paid reviews on blogs and whatnot, see for example Andy’s problem with his honest reviews which Google classifies as paid links, and of course all sorts of traffic deals, affiliate links, banner ads and stuff like that.

You don’t even need to label a clean link as advert or sponsored. If the link destination matches a domain in Google’s database of on-line advertisers, link buyers, e-commerce sites / merchants etcetera, or Google figures out that you link too much to affiliated sites or other sites you own or control, then your toolbar PageRank is toast and most probably your outgoing links will be penalized. Possibly these penalties have impact on your internal links too, what results in less PageRank landing on subsidiary pages. Less PageRank gathered by your landing pages means less crawling, less ranking, less SERP referrers, less revenue.

The solution

You’re absolutely right when you say that such search engine nitpicking should not force you to throw nofollow crap on your links like confetti. From your and my point of view condomizing links is wrong, but sometimes it’s better to pragmatically comply to such policies in order to stay in the game.

Although uncrawlable redirect scripts have advantages in some cases, the simplest procedure to condomize a link is the rel-nofollow microformat. Here is an example of a googlified affiliate link:
<a href="http://sponsor.com/?affID=1" rel="nofollow">Sponsor</a>

Why serve your visitors search engine crawler directives?

Complying to Google’s laws does not mean that you must deliver crawler directives like rel=”nofollow” to your visitors. Since Google is concerned about search engine rankings influenced by uncondomized links with commercial intent, serving crawler directives to crawlers and clean links to users is perfectly in line with Google’s goals. Actually, initiatives like the X-Robots-Tag make clear that hiding crawler directives from users is fine with Google. To underline that, here is a quote from Matt Cutts:

[…] If you want to sell a link, you should at least provide machine-readable disclosure for paid links by making your link in a way that doesn’t affect search engines. […]

The other best practice I’d advise is to provide human readable disclosure that a link/review/article is paid. You could put a badge on your site to disclose that some links, posts, or reviews are paid, but including the disclosure on a per-post level would better. Even something as simple as “This is a paid review” fulfills the human-readable aspect of disclosing a paid article. […]

Google’s quality guidelines are more concerned with the machine-readable aspect of disclosing paid links/posts […]

To make sure that you’re in good shape, go with both human-readable disclosure and machine-readable disclosure, using any of the methods [uncrawlable redirects, rel-nofollow] I mentioned above.
[emphasis mine]

Since Google devalues paid links anyway, search engine friendly cloaking of rel-nofollow for Googlebot is a non-issue with advertisers, as long as this fact is disclosed. I bet most link buyers look at the magic green pixels anyway, but that’s their problem.

How to cloak rel-nofollow for search engine crawlers

I’ll discuss a PHP/Apache example, but this method is adaptable to other server sided scripting languages like ASP or so with ease. If you’ve a static site and PHP is available on your (*ix) host, you need to tell Apache that you’re using PHP in .html (.htm) files. Put this statement in your root’s .htaccess file:
AddType application/x-httpd-php .html .htm

Next create a plain text file, insert the code below, and upload it as “funct_nofollow.php” or so to your server’s root directory (or a subdirectory, but then you need to change some code below).
<?php
function makeRelAttribute ($linkClass) {
$numargs = func_num_args();
// optional 2nd input parameter: $relValue
if ($numargs >= 2) {
$relValue = func_get_arg(1) ." ";
}
$referrer = $_SERVER["HTTP_REFERER"];
$refUrl = parse_url($referrer);
$isSerpReferrer = FALSE;
if (stristr($refUrl[host], "google.") ||
stristr($refUrl[host], "yahoo."))
$isSerpReferrer = TRUE;
$userAgent = $_SERVER["HTTP_USER_AGENT"];
$isCrawler = FALSE;
if (stristr($userAgent, "Googlebot") ||
stristr($userAgent, "Slurp"))
$isCrawler = TRUE;
if ($isCrawler /*|| $isSerpReferrer*/ ) {
if ("$linkClass" == "ad") $relValue .= "advertising nofollow";
if ("$linkClass" == "paid") $relValue .= "sponsored nofollow";
if ("$linkClass" == "own") $relValue .= "affiliated nofollow";
if ("$linkClass" == "vote") $relValue .= "editorial dofollow";
}
if (empty($relValue))
return "";
return " rel=\"" .trim($relValue) ."\" ";
} // end function makeRelValue
?>

Next put the code below in a PHP file you’ve included in all scripts, for example header.php. If you’ve static pages, then insert the code at the very top.
<?php
@include($_SERVER["DOCUMENT_ROOT"] ."/funct_nofollow.php");
?>

Do not paste the function makeRelValue itself! If you spread code this way you’ve to edit tons of files when you need to change the functionality later on.

Now you can use the function makeRelValue($linkClass,$relValue) within the scripts or HTML pages. The function has an input parameter $linkClass and knows the (self-explanatory) values “ad”, “paid”, “own” and “vote”. The second (optional) input parameter is a value for the A element’s REL attribute itself. If you provide it, it gets appended, or, if makeRelValue doesn’t detect a spider, it creates a REL attribute with this value. Examples below. You can add more user agents, or serve rel-nofollow to visitors coming from SERPs by enabling the || $isSerpReferrer condition (remove the bold /*&*/).

When you code a hyperlink, just add the function to the A tag. Here is a PHP example:
print "<a href=\"http://google.com/\"" .makeRelAttribute("ad") .">Google</a>";

will output
<a href="http://google.com/" rel="advertising nofollow" >Google</a>
when the user agent is Googlebot, and
<a href="http://google.com/">Google</a>
to a browser.

If you can’t write nice PHP code, for example because you’ve to follow crappy guidelines and worst practices with a WordPress blog, then you can mix HTML and PHP tags:
<a href="http://search.yahoo.com/"<?php print makeRelAttribute("paid"); ?>>Yahoo</a>

Please note that this method is not safe with search engines or unfriendly competitors when you want to cloak for other purposes. Also, the link condoms are served to crawlers only, that means search engine staff reviewing your site with a non-crawler user agent name won’t spot the nofollow’ed links unless they check the engine’s cached page copy. An HTML comment in HEAD like “This site serves machine-readable disclosures, e.g. crawler directives like rel-nofollow applied to links with commercial intent, to Web robots only.” as well as a similar comment line in robots.txt would certainly help to pass reviews by humans.

A Google-friendly way to handle paid links, affiliate links, and cross linking

Load this page with different user agents and referrers. You can do this for example with a FireFox extension like PrefBar. For testing purposes you can use these user agent names:
Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)
Mozilla/5.0 (compatible; Yahoo! Slurp; http://help.yahoo.com/help/us/ysearch/slurp)

and these SERP referrer URLs:
http://google.com/search?q=viagra
http://search.yahoo.com/search?p=viagra&ei=utf-8&iscqry=&fr=sfp

Just enter these values in PrefBar’s user agent respectively referrer spoofing options (click “Customize” on the toolbar, select “User Agent” / “Referrerspoof”, click “Edit”, add a new item, label it, then insert the strings above). Here is the code above in action:

Referrer URL:
User Agent Name: CCBot/2.0 (http://commoncrawl.org/faq/)
Ad makeRelAttribute(”ad”): Google
Paid makeRelAttribute(”paid”): Yahoo
Own makeRelAttribute(”own”): Sebastian’s Pamphlets
Vote makeRelAttribute(”vote”): The Link Condom
External makeRelAttribute(”", “external”): W3C rel="external"
Without parameters makeRelAttribute(”"): Sphinn

When you change your browser’s user agent to a crawler name, or fake a SERP referrer, the REL value will appear in the right column.

When you’ve developed a better solution, or when you’ve a nofollow-cloaking tutorial for other programming languages or platforms, please let me know in the comments. Thanks in advance!



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Google and Yahoo accept undelayed meta refreshs as 301 redirects

Although the meta refresh often gets abused to trick visitors into popup hells by sneaky pages on low-life free hosts (poor man’s cloaking), search engines don’t treat every instance of the meta refresh as Webspam. Folks moving their free hosted stuff to their own domains rely on it to redirect to the new location:
<meta http-equiv=refresh content="0; url=http://example.com/newurl" />

Yahoo clearly states how they treat a zero meta refresh, that is a redirect with a delay of zero seconds:

META Refresh: <meta http-equiv=”refresh” content=…> is recognized as a 301 if it specifies little or no delay or as a 302 if it specifies noticeable delay.

Google is in the process of rewriting their documentation, in the current version of their help documents the meta refresh is not (yet!) mentioned. The Google Mini treats all meta refreshs as 302:

A META tag that specifies http-equiv=”refresh” is handled as a 302 redirect.

but that’s handled differently on the Web. I’ve asked Google’s search evangelist Adam Lasnik and he said:

[The] best idea is to use 301/302s directly whenever possible; otherwise, next best is to do a metarefresh with 0 for a 301. I don’t believe we recommend or support any 302-alternative.

Thanks Adam! I’ll update the last meta refresh thread.

If you have the chance to do 301 redirects don’t mess with the meta refresh. Utilize this method only when there’s absolutely no other chance.

Full stop for search geeks. What follows is an explanation for not that experienced Webmasters in need to move their stuff away from greedy Web content funeral services, aka free hosts of any sort.

Ok, now that we know the major search engines accept an undelayed meta refresh as poor man’s 301 redirect, how should a page having this tag look like in order to act as a provisional permanent redirect? As plain and functional as possible:
<html>
<head>
<title>Moved to new URL: http://example.com/newurl</title>
<meta http-equiv=refresh content="0; url=http://example.com/newurl" />
<meta name="robots" content="noindex,follow" />
</head>
<body>
<h1>This page has been moved to http://example.com/newurl</h1>
<p>If your browser doesn't redirect you to the new location please <a href="http://example.com/newurl"><b>click here</b></a>, sorry for the hassles!</p>
</body>
</html>

As long as the server delivers the content above under the old URL sending a 200-OK, Google’s crawl stats should not list the URL under 404 errors. If it does appear under “Not found”, something went awfully bad, probably on the free host’s side. As long as you’ve control over the account, you must not delete the page because the search engines revisit it from time to time checking whether you still redirect with that URL or not.

[Excursus: When a search engine crawler fetches this page, the server returns a 200-OK because, well, it’s there. Acting as a 301/302 does not make it a standard redirect. That sounds confusing to some people, so here is the technical explanation. Server sided response codes like 200, 302, 301, 404 or 410 are sent by the Web server to the user agent in the HTTP header before the server delivers any page content to the user agent (Web browser, search engine crawler, …). The meta refresh OTOH is a client sided directive telling the user agent to disregard the page’s content and to fetch the given (new) URL to render it instead of the initially requested URL. The browser parses the redirect directive out of the file which was received with a HTTP response code 200 (OK). That’s why you don’t get a 302 or 301 when you use a server header checker.]

When a search engine crawler fetches the page above, that’s just the beginning of a pretty complex process. Search engines are large scaled systems which make use of asynchronous communication between tons of highly specialized programs. The crawler itself has nothing to do with indexing. Maybe it follows server sided redirects instantly, but that’s unlikely with meta refreshs because crawlers just fetch Web contents for unprocessed delivery to a data pool from where all sorts of processes like (vertical) indexers pull their fodder. Deleting a redirecting page in the search index might be done by process A running hourly, whilst process B instructing the crawler to fetch the redirect’s destination runs once a day, then the crawler may be swamped so that it delivers the new content a month later to process C which ran just five minutes before the content delivery and starts again not before next Monday if that’s not a bank holiday…

That means the old page may gets deindexed way before the new URL makes it in the search index. If you change anything during this period, you just confuse the pretty complex chain of processes what means that perhaps the search engine starts over by rolling back all transactions and refetching the redirecting page. Not good. Keep all kind of permanent redirects forever.

Actually, a zero meta refresh works like a 301 redirect because the engines (shall) treat is as a permanent redirect, but it’s not a native 301. In fact, due to so much abuse by spammers it might be considered less reliable than a server sided 301 sent in the HTTP header. Hence you want to express your intention clearly to the engines. You do that with several elements of the meta refresh’ing page:

  • The page title says that the resource was moved and tells the new location. Words like “moved” and “new URL” without surrounding gimmicks clear the message.
  • The zero (second) delay parameter shows that you don’t deliver visible content to (most) human visitors but switch their user agent right to the new URL.
  • The “noindex” robots meta tag telling the engines not to index the actual page’s contents is a signal that you don’t cheat. The “follow” value (referring to links in BODY) is just a fallback mechanismn to ensure that engines having troubles to understand the redirect at least follow and index the “click here” link.
  • The lack of indexable content and keywords makes clear that you don’t try to achieve SE rankings for anything except the new URL.
  • The H1 heading repeating the title tag’s content on the page, visible for users surfing with meta refresh = off, accelerates the message and helps the engines to figure out the seriousness of your intent.
  • The same goes for the text message with a clear call for action underlined with the URL introduced by other elements.

Meta refreshs like other client sided redirects (e.g. window.location = "http://example.com/newurl"; in JavaScript) can be found in every spammer’s toolbox, so don’t leave the outdated content on the page and add a JavaScript redirect only to contentless pages like the sample above. Actually, you don’t need to do that, because the number of users surfing with meta-refresh=off is only a tiny fraction of your visitors, and using JavaScript redirects is way more risky (WRT picky search engines) than a zero meta refresh. Also, JavaScript redirects –if captured by a search engine– should count as 302 and you really don’t want to deal with all the disadvantages of soft redirects.

Another interesting question is whether removing the content from the outdated page makes a difference or not. Doing a mass search+replace to insert the meta tags (refresh and robots) with no further changes to the HTML source might seem attractive from a Webmaster’s perspective. It’s fault-prone however. Creating a list mapping outdated pages to their new locations to feed a quick+dirty desktop program generating the simple HTML code above is actually easier and eliminates a couple points of failure.

Finally: Make use of meta refreshs on free hosts only. Professional hosting firms let you do server sided redirects!



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