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17th Apr 2009
Canonical Tag is Solution for Duplicate Content – Part2

The new “Canonical tag” and its use.
Today with the increasing traffic on internet the issue of duplicate content is on a rise.

The searcher only want to see unique results and therefore search engines try to index and display the original or “canonical” content. This is creating a serious thought for site owners as they fear that due to duplicate content their site will be filtered or penalized by the search engines and they may lose their rankings.


So the major search engines (links are to their separate announcements) have put a joint effort to solve this issue and reduce content cluster. If you are new to this and want to know what canonical means, please read on for a detailed explanation.

What is a canonical issue ?

One page has Multiple URLs
There are many definitions for duplicate content, but the major and most important part to be taken care of is, multiple URLs pointing to the same page. Due to this you could end up with 100 pages having 10 URLs for each and every page this would result in the need for search engines to sort 1000 URL’s which may not be positively promising for your site.


All the URLs stated above are directing user to the same page but these URLs are created unintentionally and the webmaster has no evil intentions, but if this is not specified to the search engines it would result negatively. Due to this the need of canonical tag arise so that the webmasters can hint the search engines about the issue and see that it crawls and indexes only the original URL.

Couple of reasons to define it a problem.

Site may not be properly crawled – Based on numerous factors the crawlers allot a limited amount of time on each site. Now if the crawler has set time for only 100 pages of your site, you will obviously wish those are 100 unique pages and not the same 10 pages with 10 different URLs.
Loss of link credit – If a single page has 10 different URLs pointing to it then there is a possibility that other sites maybe linking to it in 10 different ways. Thus the link credit will be shared between 10 URLs, and get the value of original page diluted.

The new canonical tag and its use.

Specify the canonical version using a tag in the head section of the page as follows:

That’s it! But see that you don’t forget that “/” at the end.

  • The tag can be used only on pages within a single site (sub domains and subfolders are fine).
  • Absolute links are recommended but you can use both absolute as well as relative links.
  • The working of this tag is similar to a 301 redirect for all the URLs showing the page with canonical tag.
  • All the links to URLs will be consolidated to the URL specified as canonical.
  • This is not a directive for a search engine it’s just a strong hint as Google calls it “Suggestions that we honor strongly” so don’t misunderstand it as a directive for search engine crawlers you can never order them.
  • Search engines will consider this URL a “strong hint” as to which URL should be crawled and indexed so that only one URL is crawled and indexed thus not arising the canonical issue.

How and where it should be used

The correct use of this tag is when:-

  • When each URL has similar or exactly the same content.
  • The URL uses simple and easy to understand parameter patterns (such as using ? and %) which most of us are used to.
  • The canonical URL is the shortest proper version of a particular URL

For eg in this case the one highlighted should be the canonical URL


Can this tag be abused by spammers?

Maybe they give it a try, but authorities from Google says that the same security that prevent abuse in other methods (such as redirects) are in place here as well, and that Google reserves the right to take action if it finds a site using the tag to manipulate search engines and violate search engine guidelines.

Other thing is that this tag will only work with very similar or identical content, so you can’t use it to send all of the link value from the less important pages of your site to the more important ones. In case of conflict such as pages point to each other as canonical, the URL specified as canonical redirects to a non-canonical version, or the page specified as canonical doesn’t exists, search engines will sort things out and make their own decision just as they do now, and will decide which URL they think is the best canonical version.

The tag will most helpful in the case of multiple URLs pointing at the same page, but can also be used when multiple versions of a single page exist.

The search engines pressure the point that it’s still important to build good URL structure but if you are not able to implement this tag, they will still keep the current process ongoing to determine the canonical.

Search engines are very intelligent and efficient and can detect the canonical by themselves sort them and also take the shortest one as canonical URL.

This tag may not completely solve the issue of duplicate content, but will surely help make things better and a bit easier for the site owners facing this problems particularly sites for ecommerce etc who really need all the help they can get in the current economy. The site owners have been asking for something like this for quite a long time so this new tag is going to get a great welcome by the web and webmasters.


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