Last week Google, Yahoo, and Microsoft announced support for a new link element to clean up duplicate urls on sites. The syntax is pretty simple: An ugly url such as http://www.example.com/page.html?sid=asdf314159265 can specify in the HEAD part of the document the following:
<link rel="canonical" href="http://example.com/page.html"/>
That tells search engines that the preferred location of this url (the “canonical” location, in search engine speak) is http://example.com/page.html instead of http://www.example.com/page.html?sid=asdf314159265 .
I also did a three-minute video with WebProNews after the announcement to describe the tag, and you can watch the canonical link element video for another way to learn about it. Watching the video is the easiest way to learn about this new element quickly.
Also exciting is that Joost de Valk has already produced several plug-ins. Joost made a canonical plug-in for WordPress, a plugin for e-commerce software package Magento, and also a plug-in for Drupal. I’d expect people to make plug-ins for other software packages pretty soon, or modify the software to use this link element in the core software.
Thanks to the folks at Yahoo (e.g. Priyank Garg and others) and Microsoft (e.g. Nathan Buggia and others) who built consensus to support this open standard. On the Google side, Joachim Kupke did all the implementation and indexing work to make this happen; thanks for the heavy lifting on this, Joachim. I want to send a special shout-out to Greg Grothaus as well. Although people had discussed similar ideas in the past, Greg was a catalyst at Google and his proposal really got the ball rolling on this idea; read more about it on his blog.
If you’re interested, you can see the slides I presented last week to announce this new element:
I’ll be happy to try to answer questions if you’ve got ’em, or you can ask questions on the official Google webmaster blog. If you’re going to SES London this week, Google’s own Maile Ohye will be at SES London to answer questions as well.
Update: I had “value” instead of “href” in the link element. Serves me right for not double-checking, and thanks to the commenters who noticed!
Update, 2/23/2009: Ask just announced that they will support the canonical link element. That means all the major search engines will be supporting this tag, which is great news for site owners, developers, and webmasters. Yay!