This is hot off the presses, folks.
Google, Yahoo, and Microsoft announced today that their search engines will honor a new value for the
rel attribute of
link elements commonly found in the
head element of a web page. This new specification aims to reduce content duplication via redundant URLs.
For instance, WordPress posts can be accessed always through the URL
example.com/index.php?p=3 and often through a URL such as
example.com/2009/02/12/search-engines-to-honor-canonical-urls or the like. Search engines see these separate URLs and usually think that they are duplicate content at different URLs, thus reducing the site’s ranking because of the duplicate content.
The new functionality acts not unlike a soft 301 redirect.
Joost de Valk wrote a WordPress plugin called wp-canonical which adds such a
link element to any WordPress blog. I’m using it now. He’s also written a Drupal plugin and an informative blog about about canonical URLs, too. That was quick!