"Nofollow"
provides a way for webmasters to tell search engines "Don't follow
links on this page" or "Don't follow this specific link."
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:
<meta name="robots" content="nofollow" />
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:
<a href="signin.php" rel="nofollow">sign in</a>
How does Google handle nofollowed links?
In general, we don't follow them. This 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.
However, the target pages may still appear in our index if other sites
link to them without using
nofollow, or if the URLs are submitted to Google in a Sitemap. Also, it's important to note that other search engines may handle
nofollow in slightly different ways.
What are Google's policies and some specific examples of nofollow usage?
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. This can discourage spammers from targeting your site, and
will help keep your site from inadvertently passing PageRank to bad
neighborhoods on the web. In particular, comment spammers
may decide not to target a specific content management system or blog
service if they can see that untrusted links in that service are
nofollowed. If you want to recognize and reward trustworthy
contributors, you could decide to automatically or manually remove the
nofollow attribute on links posted by members or users who have consistently made high-quality contributions over time.
- 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. Search engine guidelines require machine-readable
disclosure of paid links in the same way that consumers online and
offline appreciate disclosure of paid relationships (for example, a
full-page newspaper ad may be headed by the word "Advertisement"). More information on Google's stance on paid 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. However, a solid information architecture —
intuitive navigation, user- and search-engine-friendly URLs, and so on —
is likely to be a far more productive use of resources than focusing on
crawl prioritization via nofollowed links.
How does nofollow work with the Social Graph API (rel="nofollow me")?
If you host user profiles and allow users to link to other profiles
on the web, we encourage you to mark those links with the rel="me"
microformat so that they can be made available through the Social Graph
API. For example:
<a href="http://blog.example.com" rel="me">My blog</a>
However, because these links are user-generated and may sometimes
point to untrusted pages, we recommend that these links be marked with
nofollow. For example:
<a href="http://blog.example.com" rel="me nofollow">My blog</a>
With
rel="me nofollow", Google will continue to treat the
rel="nofollow" as expected for search purposes, such as not transferring PageRank. However, for the Social Graph API, we will count the
rel="me" link even when included with a
nofollow.
If you are able to verify ownership of a link using an identity technology such as
OpenID or
OAuth, however, you may choose to remove the
nofollow link.
To prevent crawling of a rel="me nofollow" URL, you can use
robots.txt. Standard robots.txt exclusion rules are respected by both Googlebot and the Social Graph API.
updated
03/14/2012
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