Nofollow

nofollow is an HTML attribute value used to instruct some search engines that a hyperlink should not influence the link target's ranking in the search engine's index. It is intended to reduce the effectiveness of certain types of search engine spam, thereby improving the quality of search engine results and preventing spamdexing from occurring in the first place.

Concept and specification

The concept for the specification of the attribute value nofollow was designed by Google’s head of webspam team Matt Cutts and Jason Shellen from Blogger.com in 2005. [http://microformats.org/wiki/rel-nofollow rel="nofollow" Specification] , "Microformats.org", retrieved June 17, 2007]

The specification for nofollow is copyrighted 2005-2007 by the authors and subject to a royalty free patent policy, e.g. per the W3C Patent Policy 20040205, [ [http://www.w3.org/Consortium/Patent-Policy-20040205/ W3C Patent Policy 20040205] ,"W3.ORG"] and IETF RFC 3667 & RFC 3668. The authors intend to submit this specification to a standards body with a liberal copyright/licensing policy such as the GMPG, IETF, and/or W3C. [http://microformats.org/wiki/rel-nofollow rel="nofollow" Specification] , "Microformats.org", retrieved June 17, 2007]

What nofollow is not for

The nofollow attribute value is not meant for blocking access to content or preventing content to be indexed by search engines. The proper methods for blocking search engine spiders to access content on a website or for preventing them to include the content of a page in their index are the Robots Exclusion Standard (robots.txt) for blocking access and on page Meta Elements that are designed to specify on an individual page level what a search engine spider should or should not do with the content of the crawled page.

Introduction and support

Google announced in early 2005 that hyperlinks with rel="nofollow" attribute [W3C (December 24, 1999), [http://www.w3.org/TR/REC-html40/struct/links.html#adef-rel HTML 4.01 Specification] , "W3C.org", retrieved May 29, 2007] would not influence the link target's PageRank. In addition, the Yahoo and Windows Live search engines also respect this tag. [Google (January 18, 2006), [http://googleblog.blogspot.com/2005/01/preventing-comment-spam.html Preventing comment spam] , "Official Google Blog", retrieved on May 29, 2007]

How the attribute is being interpreted differs between the search engines. While some take it literally and do not follow the link to the page being linked to, others still "follow" the link to find new web pages for indexing. In the latter case rel="nofollow" actually tells a search engine "Don't score this link" rather than "Don't follow this link." This differs from the meaning of nofollow as used within a robots meta tag, which does tell a search engine: "Do not follow any of the hyperlinks in the body of this document.".

Interpretation by the individual search engines

While all engines that support the attribute exclude links that use the attribute from their ranking calculation, the details about the exact interpretation of the attribute vary from search engine to search engine. [Loren Baker (April 29, 2007), [http://www.searchenginejournal.com/how-google-yahoo-askcom-treat-the-no-follow-link-attribute/4801/ How Google, Yahoo & Ask.com Treat the No Follow Link Attribute] , "Search Engine Journal", retrieved May 29, 2007] Michael Duz (December 2, 2006), [http://www.seo-blog.com/rel-nofollow.php rel=”nofollow” Google, Yahoo and MSN] , "SEO Blog", retrieved May 29, 2007]

*Google states that their engine takes "nofollow" literally and does not "follow" the link at all. However, experiments conducted by SEOs show conflicting results. These studies reveal that Google does follow the link, but does not index the linked-to page, unless it was in Google's index already for other reasons (such as other, non-nofollow links that point to the page).Michael Duz (December 2, 2006), [http://www.seo-blog.com/rel-nofollow.php rel=”nofollow” Google, Yahoo and MSN] , "SEO Blog", retrieved May 29, 2007] Links with "nofollow" are included in the backlinks reporting data at Google's Webmaster Central. [http://www.bubub.org/rel_nofollow_test.html Rel Nofollow Test] from August 2007]
*Yahoo! "follows it", but excludes it from their ranking calculation.
*MSN Search respects "nofollow" as regards not counting the link in their ranking, but it is not proven whether or not MSN follows the link.
*Ask.com ignores the attribute altogether.

Use by weblog software

Most weblog software marks reader-submitted links this way by default (with no option to disable it without code modification).A more sophisticated server software could spare the nofollow for links submitted by trusted users like those registered for a long time, on a whitelist, or with a high good karma. Some server software adds rel="nofollow" to pages that have been recently edited but omits it from stable pages, under the theory that stable pages will have had offending links removed by human editors.

The widely used blogging platform WordPress versions 1.5 and above automatically assign the nofollow attribute to all user-submitted links (comment data, commenter URI, etc). [Codex Documentation, [http://codex.wordpress.org/Nofollow Nofollow] , "Wordpress.org Documentation", retrieved May 29, 2007] However, there are several free plugins available that automatically remove the nofollow attribute value. [WordPress Plugins, [http://wordpress.org/extend/plugins/tags/nofollow Plugins tagged as Nofollow] , "WordPress Extensions", retrieved March 10, 2008]

Use on other websites

MediaWiki software, which powers Wikipedia, was equipped with nofollow support soon after initial announcement in 2005. The option was enabled on most Wikipedias. One of the prominent exceptions was the English Wikipedia. Initially, after a discussion, it was decided not to use rel="nofollow" in articles and to use a URL blacklist instead. In this way, English Wikipedia contributed to the scores of the pages it linked to, and expected editors to link to relevant pages.

In May 2006, a patch to MediaWiki software allowed to enable nofollow selectively in namespaces. This functionality was used on pages that are not considered to be part of the actual encyclopedia, such as discussion pages and resources for editors. [Wikipedia (May 29, 2006), [http://en.wikipedia.org/wiki/Wikipedia:Wikipedia_Signpost/2006-05-29/Technology_report Wikipedia Signpost/2006-05-29/Technology report] , "Wikipedia.org", retrieved May 29, 2007] Following increasing spam problems and a within-Foundation order from Jimmy Wales, rel="nofollow" was added to article-space links in January 2007. [Brion Vibber (January 20, 2007), [http://lists.wikimedia.org/pipermail/wikien-l/2007-January/061137.html Nofollow back on URL links on en.wikipedia.org articles for now] , "Wikimedia List WikiEN-l", retrieved May 29, 2007] [] However, the various interwiki templates and shortcuts that link to other Wikimedia Foundation projects and many external wikis such as Wikia are not affected by this policy.

Other websites like Slashdot, with high user participation, use improvised nofollow implementations like adding rel="nofollow" only for potentially misbehaving users. Potential spammers posing as users can be determined through various heuristics like age of registered account and other factors. Slashdot also uses the poster's karma as a determinant in attaching a nofollow tag to user submitted links.

A number of social bookmarking and photo sharing websites also use the rel="nofollow" tag for their outgoing links, including: Digg.com, Furl, Propeller.com (formerly Netscape.com), Yahoo! My Web 2.0, YouTube, and Technorati Favs. [Loren Baker (November 15, 2007), [http://www.searchenginejournal.com/social-bookmarking-sites-which-dont-use-nofollow-bookmarks-and-search-engines/5985/ Social Bookmarking Sites Which Don’t Use NoFollow Bookmarks and Search Engines] , "Search Engine Journal", retrieved on December 16, 2007]

Repurpose for paid links

While the effectiveness of the nofollow attribute to prevent comment spam is in doubt and raises other issues instead, [Jeremy Zawodny (May 30, 2006), [http://jeremy.zawodny.com/blog/archives/006800.html Nofollow No Good?] ,"Jeremy Zawodny's Blog", retrieved June 17, 2007] search engines have moved ahead and attempted to repurpose the attribute for something different. Google began suggesting the use of nofollow also as a machine-readable disclosure for paid links, so that these links do not get credit in search engines results. [Matt Cutts (September 1, 2005), [http://www.mattcutts.com/blog/text-links-and-pagerank/ Text links and PageRank] , "Matt Cutts Blog", retrieved June 17, 2007]

The growth of the link buying economy, where companies' entire business models are based on paid links that affect search engine rankings, [Philipp Lenssen (April 19, 2007), [http://blog.outer-court.com/archive/2007-04-19-n50.html The Paid Links Economy] ,"Google Blogoscoped", retrieved June 17, 2007] caused the debate about the use of nofollow in combination with paid links to move into the center of attention of the search engines, who started to take active steps against link buyers and sellers. [Matt Cutts (April 14, 2007 ), [http://www.mattcutts.com/blog/how-to-report-paid-links/ How to report paid links] , "Matt Cutts Blog", retrieved June 17, 2007] This triggered a very strong response from web masters. [Carsten Cumbrowski (May 14th, 2007), [http://www.searchenginejournal.com/matt-cutts-update-on-paid-links-discussion-qa/4907/ Matt Cutts on Paid Links Discussion - Q&A] , "SearchEngineJournal.com", retrieved June 17, 2007]

Nofollow to control internal PageRank flow

Search engine optimization professionals started using the nofollow attribute to control the flow of PageRank within a website. This is an entirely different use than it was intended originally. Nofollow was designed to control the flow of PageRank from one website to another. However, some SEOs have suggested that a nofollow used for an internal link should work just like nofollow used for external links.

Several SEOs have suggested that pages such as "About Us", "Terms of Service", "Contact Us", and "Privacy Policy" pages are not important enough to earn PageRank, and so should have nofollow on internal links pointing to them. Google employee Matt Cutts has provided indirect responses on the subject, but has never publicly endorsed this point of view. [October 8, 2007, [http://www.stonetemple.com/articles/interview-matt-cutts.shtml Eric Enge Interviews Google's Matt Cutts] , "Stone Temple Consulting", retrieved on January 20,2008]

The practice is controversial and has been challenged by some SEO professionals, including Shari Thurow [March 6, 2008, [http://searchengineland.com/080306-083414.php You'd be wise to "nofollow" this dubious advice] , "Search Engine Land"] and Adam Audette [June 3, 2008 [http://www.audettemedia.com/blog/arguments-against-nofollow 8 Arguments Against Sculpting PageRank With Nofollow] , "Audette Media"] . Site search proponents have pointed out that visitors do search for these types of pages, so using nofollow on internal links pointing to them may make it difficult or impossible for visitors to find these pages in site searches powered by major search engines.

Although proponents of use of nofollow on internal links have cited an inappropriate attribution to Matt Cutts [August 29, 2007 [http://www.seomoz.org/blog/questions-answers-with-googles-spam-guru Matt Cutts on Nofollow, Links-Per-Page and the Value of Directories] , "SEomoz"] (see Matt's clarifying comment, rebutting the attributed statement [August 29, 2007 [http://www.seomoz.org/blog/questions-answers-with-googles-spam-guru#jtc33536] , "SEOmoz comment by Matt Cutts"] ) as support for using the technique, Cutts himself never actually endorsed the idea. Several Google employees (including Matt Cutts) have urged Webmasters not to focus on manipulating internal PageRank. Google employee Adam Lasnik [February 20, 2008 [http://www.toprankblog.com/2008/02/adam-lasnik-video/ Interview with Adam Lasnik of Google] ] has publicly advised Webmasters NOT to use nofollow on internal links.

No reliable data has been published on the effectiveness or potential harm that use of nofollow on internal links may provide. Unsubstantiated claims have been challenged throughout the debate and some early proponents of the idea have subsequently cautioned people not to view the use of nofollow on internal links as a silver bullet or quick-success solution.

More general consensus seems to favor the use of nofollow on internal links pointing to user-controlled pages which may be subjected to spam link practices, including user profile pages, user comments, forum signatures and posts, calendar entries, etc.

Criticism

Some weblog authors object to the use of rel="nofollow", arguing, for example, [Michael Hampton (May 23, 2005), [http://www.homelandstupidity.us/2005/05/23/nofollow-revisited/ Nofollow revisited] , "HomelandStupidity.us", retrieved May 29, 2007] [Loren Baker (February 14, 2007), [http://www.searchenginejournal.com/13-reasons-why-nofollow-tags-suck/4410/ 13 Reasons Why NoFollow Tags Suck] , "Search Engine Journal", retrieved May 29, 2007] that
* Link spammers will continue to spam everyone to reach the sites that do not use rel="nofollow"
* Link spammers will continue to place links for clicking (by surfers), even if those links are ignored by search engines.
* Google is advocating the use of rel="nofollow" in order to reduce the effect of heavy inter-blog linking on page ranking.
* According to the statistics shown at the Akismet's antispam service [http://akismet.com/stats/] , this attribute has not stopped the comment spam and has not discouraged spammers.
* Lack of accreditation may discourage informational comments by professionals wishing to establish their PageRank reputation.

ee also

*Spam in blogs and nofollow
*Google PageRank
*Search engine optimization
*Search engine spiders, also called web crawlers
*Noindex

Blocking and excluding content from search engines

*Robots Exclusion Standard (robots.txt)
*Meta elements

References