Canonicalization: The Canonical Tag

Melanie Wahl - April 2, 2012

In our previous blog post on canonicalization we gave a brief definition and covered the most common webmaster concern of www versus non-www versioning of a domain.

This blog post will cover the canonical tag which was released in February 2009 to help website owners and their webmasters regulate how search engines sorted their content in the hope of keeping duplicate content out of each search engine’s index.

First, what is the canonical tag and what does it look like?   The canonical tag is marked by rel=”canonical” and is placed in the header of the source code for a webpage.

Here is an example:

<link rel=”canonical” href=”” />

This tag notes that the URL version listed as the href would be the version that is canonical, or preferred by you, the webmaster.   It should be noted that rel=”canonical” is not the same as a 301 redirect.   The 301 redirect automatically re-directs both search engine bots and human visitors to your perferred version of the page. The canonical tag is only ever seen by search engine bots, not users.   A 301 redirect is also considered a stronger signal that there is a canonical source, whereas the canonical tag is taken as more of a suggestion and may be overruled by the search engines if their analysis or algorithms see that a different page seems to be a better fit.   The canonical tag also has cross-domain functionality; it can be used in cases where it may not be easy to set up redirects, such as when you are migrating from one domain to another and are unable to create server-side redirects.   Google has stated that they consider the rel=”canonical” link element as a hint or suggestion and not as an absolute directive.

These two techniques can help webmasters convey to the search engines which version of their webpages to include (or exclude if needed) from the indices and how they prefer link metrics (such as link juice) to be assigned.   Contact MoreVisibility if you need help with the canonicalization of your website.

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