Executing the Canonical Link Element

On page SEO301.com/canonical-link-element-2?session=oicu812 include the following code within the header…

<link rel=”canonical” href=”SEO301.com/canonical-link-element-2″/>

notice the closing “/”

About the Canonical Link Element

Similar to a 301 but executed on a live page is the canonical (preferred) link element. This page attribute allows you to fix those nasty query strings and multiple duplicate content issues on product pages. You basically tell the search engines”I know you are on this page but you should really be over here”. This standard was accepted by Google, Yahoo and Bing on February 12th 2009 and has quickly become an open industry standard. February 12th 2009 also marks the 200th anniversary of the birth of Charles Darwin. Much like his scientific theories, this marks the evolution of the web by enabling webmasters to control more of their content flow.

The canonical link element was introduced to handle one of the most important aspects of SEO and that is the handling of duplicate content.

Consider the following URL samples. Each of these pages could return unique content but in most cases will duplicate the home page. In face you can double these if you replicate your efforts on a secure server (https).  In practice these results will generally produce the same page.

  • www.seo301.com
  • seo301.com
  • www.seo301.com/
  • seo301.com/
  • www.seo301.com/index.html
  • seo301.com/index.html
  • www.seo301.com/Home.aspx
  • seo301.com/Home.aspx

There are multiple ways you can go about fixing the issue above.  The first is simple setting up the proper 301 redirects to make sure all incoming traffic is directed to the proper page.  This assumes you have access to the server.  In addition you should make sure your content management system (CMS) is configured in such a way that it produces clean content without much duplication.  If you have a Google Webmastertools account you can actually select if you want the www or non-www version of your name to be the default.  The other thing that Google tries to to is to break the ties between two pages by looking at your sitemap.  It will use the sitemap as a directive in order to determine which page should get credit for the content.  Obviously there is also the canonical link element that acts as a final determining factor of duplicate content.

The main reason canonical link elements will remain an integral part of the SEO method of operations is the fact that you can never control how people link to you.  There will also be the unavoidable times when a client of yours is stuffing in session/affiliate IDs or populating insane query string paramaters in URL and refuse to fix them because of their “legacy back end coding standards”.

Supported Link Types of the Canonical Link Element

  • absolute URLs
  • relative URLs
  • Cross sub-domain URLs
  • Same page reference
  • Slight differences in page content
  • Chaining URLs (not advised)
  • Empty hrefs (will point page to itself)
  • Cross domain URLs

Note: On December 15th 2009 Google announced support of cross-domain canonical linking.

Matt Cutts on the Canonical Link Element