The nofollow tag was introduced by Matt Cutts and Jason Shellen from Blogger.com as a means of combating spam. The basic concept of the nofollow is to notify Google search bots do not credit any links with a rel=”nofollow” tag attached to them. Google advised webmasters to nofollow all the unwanted, unrelated links so that Google could improve their searches, by eliminating any false links.
Originally, the nofollow attribute appeared in the page-level meta tag, and instructed search engines not to follow (i.e., crawl) any outgoing links on the page. For example:
Before nofollow was used on individual links, preventing robots from following individual links on a page required a great deal of effort (for example, redirecting the link to a URL blocked in robots.txt). That’s why the nofollow attribute value of the rel attribute was created. This gives webmasters more granular control: instead of telling search engines and bots not to follow any links on the page, it lets you easily instruct robots not to crawl a specific link. For example:
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This also means that Google does not transfer PageRank or anchor text across these links. Essentially, using nofollow causes us to drop the target links from our overall graph of the web.
According to Google, here are some cases in which you might want to consider using nofollow:
- Untrusted content: If you can’t or don’t want to vouch for the content of pages you link to from your site — for example, untrusted user comments or guestbook entries — you should nofollow those links
- Paid links: A site’s ranking in Google search results is partly based on analysis of those sites that link to it. In order to prevent paid links from influencing search results and negatively impacting users, we urge webmasters use nofollow on such links
- Crawl prioritization: Search engine robots can’t sign in or register as a member on your forum, so there’s no reason to invite Googlebot to follow “register here” or “sign in” links. Using nofollow on these links enables Googlebot to crawl other pages you’d prefer to see in Google’s index.
* Check out Official Google blog regarding the usage of “nofollow” tag
