It’s rare to see the three big search engines (Google, Yahoo! and MSN) working together on a SEO standard, but at the SMX conference this week, they announced unanimous support for a new tag to address canonicalization issues.
For those of you unfamiliar with canonicalization, here’s wikipedia’s definition as a quick intro:
“canonicalization … is a process for converting data that has more than one possible representation into a “standard” canonical representation.”
Let’s look at a quick example:
The following two URLs point to the same web page:
Although the second one only has analytics tracking attached to the end; the search engines view the two URLs as different. And accordingly link value is shared across them both, which is undesirable from an SEO point of view.
The three big search engines, Google, Yahoo! and MSN have all agreed to the manage canonicalization issue with the use of a common tag.
Placed in the section of your web page, the tag looks like this:
<link rel=”canonical” href=”http://www.yourdomain.com/webpage1/”/>
For those of you who are a bit technical, here’s some info from Yahoo! on the implementation of the tag:
- The URL paths in the <link> tag can be absolute or relative, though we recommend using absolute paths to avoid any chance of errors.
- A <link> tag can only point to a canonical URL form within the same domain and not across domains. For example, a tag on http://test.example.com can point to a URL on http://www.example.com but not on http://yahoo.com or any other domain.
- The <link> tag will be treated similarly to a 301 redirect, in terms of transferring link references and other effects to the canonical form of the page.
- We will use the tag information as provided, but we’ll also use algorithmic mechanisms to avoid situations where we think the tag was not used as intended. For example, if the canonical form is non-existent, returns an error or a 404, or if the content on the source and target was substantially distinct and unique, the canonical link may be considered erroneous and deferred.
- The tag is transitive. That is, if URL A marks B as canonical, and B marks C as canonical, we’ll treat C as canonical for both A and B, though we will break infinite chains and other issues.
This is a significant enhancement by the search engines, and will be welcomed by SEOers and site owners worldwide. Canonicalization issues have been a major frustration for some time, especially when your online marketing (AdWords, email etc) uses campaign tracking.
For more information on the new canonicalization tag – visit the Yahoo! release post.