The Canonical URL Tag – Big Step for SEO

What is a Canonical URL Tag?

Every SEO expert knows that one of the biggest problems we face is duplicate content. When there are two different URLs for one page, the search engine is never clear on how to treat them. It has to decide which page to show for a specific keyword, which page to give the PageRank to and which page to consider as the main authority. It may also divide the authority and page rank, an action that will only take away from the page you’re trying to promote.

There are many ways to create duplicate content. Here are only few::
-    Different URL format for the same page (sort parameters are very popular here)
-    Print versions of pages
-    refid parameters (affiliates etc)
-    Different search query results and navigation issues

The canonical URL tag is a joint initiative of Google, MSN and Yahoo. All three united in order to create a common tag called “canonical URL tag”. This tag lets all the three big search engines know which of the duplicate pages is the main one and it can then pass all the authority, link juice and main focus of the robot to that right page. If there are two similar pages with slight different URLs, a canonical tag placed on the duplicate content URL will tell the robots which page it should promote. As for the importance of this tag, according to Google, “it’s a hint that we honor strongly”.

The canonical tag must be located in the header of the page should will look like this:
<link rel=”canonical” href=”http://www.compucall-usa.com/blog”>.

Why is it different from a 301 redirect?

1. As opposed to a 301 redirect that redirects the page both for the user and the search engine, the Canonical URL tag is just for search engines. Users will still be able to reach and view all your duplicate versions. Hence if you’re only trying to sort the results on a page, you can.
2. The engine will verify that the content is similar and that the use of this tag is justified. In a 301 redirect, you can decide whether the redirect is justified. Regarding how much similar the duplicate pages have to be, Google say that they “allow slight differences”.
3. The 301 URL redirect operates exclusively on a single root domain, so you can’t use this tag to redirect between two different domains.

Unclear issues

The “link juice” question is still unclear – we will have to test it and see the results.
Also, the transitivity of the links is unclear (only Yahoo mentioned that they support transitivity of this tag).

For more information, you can read Matt Cutt’s blog post and SEOMOZ’s blog post (by randfish).