No webmaster wants Google crawling their site and indexing different pages that are essentially the same thing. There are many situations on sites that, for example, sell a lot of different items in different categories or have different session IDs, where multiple URLs get crawled, diluting the value of each link.

Previously, it may have been necessary to either deal with it or nofollow a bunch of URLs to try to get Google to give more ranking to the canonical URL. The canonical is the preferred URL that you want crawled, usually the least complicated or most easily visited one.

Now, webmasters can add a rel=”canonical” tag to the non-preferred pages that suggests to Google that this is a duplicate URL and that the search engine should refer to the URL giving in the canonical tag. Simple enough.

Google does state that they reserve the right to ignore the tags, but is something they will “honor strongly.” They will not allow for canonicals on different domains, however, so webmasters should continue to use 301 redirects. However, Google will observe canonicals within a domain that redirect to a different page.

Definitely something to check out, especially if you’ve got an ecommerce site.

This entry was posted on Thursday, February 12th, 2009 at 11:23 pmand is filed under Search Engine Marketing. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.