rel=canonical: trying to get Google to understand
Published by on April 14th, 2009 Comments Off
Back in February, Google announced it had begun supporting the rel=canonical hint in determining the definitive URL for an item of content. This sounds like a one-stop solution to all our duplicate content problems.
For example, my previous post can be reached by the full URL, but also (because of the Wordpress system defaults) via
http://seowebmonkey.com/?p=113
If someone decides to link to my post using that URL, it might therefore also enter the search index in addition to the full version – thus duplicate content.
Placing a rel=canonical instruction in your page’s header can resolve this problem before it occurs. It tells the search engine which URL to use as the definitive (canonical) URL for that page of content, regardless of what was used to get there.
Here’s an example for the above page:
<link rel="canonical" href="http://seowebmonkey.com/duplicate-content-web-applications/"/>
This sits within the <head> section of your page’s html.
This link-tag is supported by Google, Yahoo, Ask.com and Microsoft Live Search.
Does it work?
Google describes its support of rel=canonical as a “hint”. This means it will use the information to determine a canonical URL, but reserves the right to do what it wants when it feels like it. This seems to be a way to cover for errors that slip through the net. Search engines are rarely predictable, and no single method should be trusted in avoiding duplicate content.
For all content management systems in particular, this is an essential addition to the page output. How rapidly Google will change any existing duplicative content URLs that are already in its index is yet to be clearly determined, and this alone will not enable webmasters to explicitly request removal of duplicative URLs via the Google Webmaster Tools interface.
Direct removal of pages from Google’s search index will be covered in my next post.
