nofollow is an HTML attribute value used to instruct 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 spamdexing, thereby improving the quality of search engine results and preventing spamdexing from occurring in the first place.

rel=”nofollow” has come to be regarded as a microformat. Microformats reuse existing attributes but extend the standard values for the attribute. “nofollow” is a custom attribute value

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.

The specification for nofollow is (C) 2005-2007 by the authors and subject to a royalty free patent policy, e.g. per the W3C Patent Policy 20040205, and IETF RFC3667 & RFC3668. 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.

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 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 would not influence the link target’s PageRank. In addition, the Yahoo and MSN search engines also respect this tag.

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 tells 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.

• Google takes “nofollow” literally and does not “follow” the link at all. That is supposedly their official statement, but experiments conducted by SEOs show conflicting results. They show instead that Google does follow the link, but 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).
• 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 does not use the attribute for anything.

Usage 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 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 version 1.5 and above automatically assigns the nofollow attribute to all user-submitted links (comment data, commenter URI, etc).

Usage 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 international Wikipedias. One of the prominent exceptions was the English language one. 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. Following increasing spam problems and a within-Foundation order from Jimmy Wales, rel=”nofollow” was added to article-space links in January 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.

Repurpose for paid links

While the effectiveness of the nofollow attribute to prevent comment spam is in doubt and raises other issues instead, 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.

The growth of the link buying economy, where company’s entire business model is based on paid links that affect search engine rankings, 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. This triggered a very strong response by the web master community in return and also raised new questions that need to be answered

Criticism

Some weblog authors object to the use of rel=”nofollow”, arguing, for example, 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.