Canonicalization: What is it and why is it important to you?

Melanie Wahl - March 30, 2012

Canonicalization is often misunderstood by website owners who are frustrated with different versions, or unintended duplicated pages, appearing in search engine results pages (SERPs). The concept behind canonicalization is that, when duplicate pages are created, there is one preferred version indicated, called the canonical version. If no canonical version is indicated, the search engines may choose one or more versions to show in their SERPs.   Canonicalization problems are common and every website owner should make sure to check on the status of their website. We featured canonicalization as one of our Top 5 Most Common SEO Mistakes in our August 2011 Newsletter.

The most common concern with canonicalization is www versus non-www of a domain in a URL. In this situation http://www.companyname.com and http://companyname.com are seen as separate pages. If each page serves a 200 OK, search engine spiders can come across each version and see them as stand alone pages, not the same page, and possibly consider one of them duplicate content. To keep this from happening, we suggest that you select which version of your domain you would like to be the canonical version and set the other version to redirect.   Let’s assume that we want http://www.companyname.com to be the canonical version. Placing redirects from every non www page to the www page would be needed to indicate to the search engines that www pages are considered the canonical version.   We also advise against any duplication of your website whether on the same domain or on other domains that you may own.

In the next blog in this series, we will cover the canonical tag.