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Handling Duplicate Content with the Canonical Tag

Author: Guest Author; Published: Jul 1, 2009; Category: Design/Development, Guest Post, Search/SEO; Tags: Design/Development, Google; 2 Comments

Note: This is a GUEST POST by Edward Kung, owner of Seedin Web Development, a company in Vancouver, British Columbia, which provides complete web development solutions.

One of the biggest problems faced by search engines is duplicate content on the internet. Usually the content belongs to the same website but is placed on the different web pages. So when search engines perform a search they come up with 10 different pages with different URLs but the same content. SEO companies have also been plagued by the same problem.

Recently major search engines like Google and Yahoo! have come up with a new way to deal with the issue of duplicate content: the canonical tag. The canonical tag is the latest tool in the fight against the duplicate content on the internet.

How to Use the Canonical Tag

The canonical tag is applied to the URLs of the web pages that hold duplicate content. Since they are to be included in the head each of the duplicate pages, you will be simply adding the preferred version of a URL. You actually instruct the search engines that the URLs in question should direct to the preferred URL designated in the canonical tag.

The canonical tag is included in the desired web page’s head section, specifying the preferred URL in the following format:

<link rel="canonical" href="http://www.xyz.com/aboutus.html" />

The tag can only be used on pages that reside on a single site. The pages may be in subdomains as well as sub folders. You can use either absolute or relative links, but search engines strongly recommend that you use absolute links to eliminate chances of errors.

The tag is transitive in nature. For an instance, if URL X marks Y as canonical, and Y in turn marks Z as canonical, Z will be treated as canonical for both X and Y. For example: If test1.xyz.com points to canonical URL test2.xyz.com and test2.xyz.com points to canonical URL final.xyz.com. Then final.xyz.com would be treated as canonical for both test1.xyz.com and test2.xyz.com.

By using the canonical tag, all the links to all the URLs with duplicate content are simply consolidated into one URL which has been specified as canonical. This URL will be considered as a "strong hint" by search engines. The canonical tag will help search engines like Google with the task of identifying duplicate URLs.

Search engines will also understand that duplicate URLs with canonical tags are all actually referring to the URL that you want the visitors to see. Such URLs are known as canonical URLs.

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2 Responses to “Handling Duplicate Content with the Canonical Tag”

1. Ray Gulick says:

   July 13, 2009 at 7:01 am

   That’s a very good question. I’ve struggled with the same issue, and I’ve not heard or read anything that clearly tells me yea or nay.
2. Introspective says:

   July 13, 2009 at 6:53 am

   Should I stop publish my articles on article directories? I used to publish my articles, but now I wander should I stop doing this, because the risk of duplicate content penalty.