Google, Yahoo and MSN Agree on the Canonical Link Tag

Canonical URL Tag Google MSN Live YahooThe latest news coming from the the three major search engines is a major improvement to how Websites are indexed by search engines. The idea of the Canonical Link Tag is that a website owner can specify a preferred version of a particular URL. What does that mean? If your site has identical or similar content (accessible through several different URLs), the Canonical link tag helps search engines calculate the most preferred URL. How Does it Operate? The tag is part of the HTML header on a web page, the same section you’d find the Title attribute and Meta Description tag. In fact, this tag isn’t new, but like nofollow, simply uses a new rel parameter. For example:

<link rel="canonical" href="">

This would tell Yahoo!, MSN or Google that this page, where you place the tag will be treated as Therefore all links, as well as content metrics a search engine would apply should tie back to that URL as though it were one and the same

The Canonical URL tag attribute will work in a same way as a 301 redirect . In essence, you’re telling the engines that multiple pages should be considered as one (which a 301 does), without actually redirecting visitors to the new URL. The major difference will be that although a 301 redirect sends all traffic (bots and human visitors), to a new page, the Canonical URL tag is just for search engines. This means you can still separately track visitors to the unique URL versions.

Here is the info from the Main Search Engines themselves:


Is rel=”canonical” a hint or a directive?
It’s a hint that we honor strongly. We’ll take your preference into account, in conjunction with other signals, when calculating the most relevant page to display in search results.

Can I use a relative path to specify the canonical, such as?
Yes, relative paths are recognized as expected with the tag. Also, if you include a link in your document, relative paths will resolve according to the base URL.

Is it okay if the canonical is not an exact duplicate of the content?
We allow slight differences, e.g., in the sort order of a table of products. We also recognize that we may crawl the canonical and the duplicate pages at different points in time, so we may occasionally see different versions of your content. All of that is okay with us.

What if the rel=”canonical” returns a 404?
We’ll continue to index your content and use a heuristic to find a canonical, but we recommend that you specify existent URLs as canonicals.

What if the rel=”canonical” hasn’t yet been indexed?
Like all public content on the web, we strive to discover and crawl a designated canonical URL quickly. As soon as we index it, we’ll immediately reconsider the rel=”canonical” hint.

Can rel=”canonical” be a redirect?
Yes, you can specify a URL that redirects as a canonical URL. Google will then process the redirect as usual and try to index it.

What if I have contradictory rel=”canonical” designations?
Our algorithm is lenient: We can follow canonical chains, but we strongly recommend that you update links to point to a single canonical page to ensure optimal canonicalization results.

Can this link tag be used to suggest a canonical URL on a completely different domain?
No. To migrate to a completely different domain, permanent (301) redirects are more appropriate. Google currently will take canonicalization suggestions into account across subdomains (or within a domain), but not across domains. So site owners can suggest vs. vs., but not vs.

Sounds great—can I see a live example?
Yes, helped us as a trusted tester. For example, you’ll notice that the source code on the URL specifies its rel=”canonical” as:


• The URL paths in the tag can be absolute or relative, though we recommend using absolute paths to avoid any chance of errors.
• A tag can only point to a canonical URL form within the same domain and not across domains. For example, a tag on can point to a URL on but not on or any other domain.
• The 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.

MSN Live!:
• This tag will be interpreted as a hint by Live Search, not as a command. We’ll evaluate this in the context of all the other information we know about the website and try and make the best determination of the canonical URL. This will help us handle any potential implementation errors or abuse of this tag.
• You can use relative or absolute URLs in the “href” attribute of the link tag.
• The page and the URL in the “href” attribute must be on the same domain. For example, if the page is found on “”, and the ”href” attribute in the link tag points to “”, the tag will be invalid and ignored.  However, the “href” attribute can point to a different subdomain. For example, if the page is found on “” and the “href” attribute in the link tag points to”, the tag will be considered valid.
• Live Search expects to implement support for this feature sometime in the near future.

There are some ready made solutions already out to implement the Canonical tag. The best we’ve seen is from and is available from his blog here.

A great article by Matt Cutts on his blog about the new Canonical Tag

Adrian Speyer

About The Author: Adrian has over 12 years experience in Digital Marketing and Analytics. He currently works as a Marketing Manager at Vanilla Forums, a modern forum software platform that allows clients to connect and engage their communities and customers. He lives and works in Montreal.

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Sunday, February 15th, 2009 at 13:50
  • Feb 27th, 2009 at 09:28 | #1

    Why is it people keep calling these attributes for ‘tags’?

    • Mark8t Staff
      Feb 28th, 2009 at 08:58 | #2

      I guess because a tag is just a tag, but an attribute means there is a specification which defines it.

  • May 21st, 2009 at 09:09 | #3

    This canonical attribute is really useful for my art shop, which is developed through magento. Magento shops suffer from duplicate content issues sometimes, but there is now a canonical plugin which helps to avoid this issue. Thanks for the thorough explanation.

  • May 28th, 2009 at 17:23 | #4

    Does the Magento canonical plugin come standard or you have to manually add it?

  • May 28th, 2009 at 17:25 | #5

    Magento is overrated if you ask me. I’ve seen it in action and it does suffer from duplicate content sometimes as well as other various issues.

    As far as having the canonical link I guess it would be helpful if you want to specify a particular link to google, but google tends to find the best content and display it. I don’t mess with what google does on its own.

  • Johnny
    Jul 29th, 2009 at 08:31 | #6

    Duplicate content from tags, categories and such has always been a concern for me. Most of the popular WordPress themes caused you to end up having some pages indexed with the tag version while others went straight to the post or category.

    This should help clean all that duplcate content up and allow us to produce better SEO blogs and websites.

  • Aug 7th, 2009 at 12:20 | #7

    Fantastic, this sorts out an issue that we have while having various different resource catalogues on our website. Will look at how we can implement this. I see a few of the posters say there are issues but we will need to try it out for ourselves.

  • Sep 30th, 2009 at 16:46 | #8

    So is this a possible way to keep your site from being hit with duplicate content if it is going to treat the page the same as your others?

  • Flush
    Nov 24th, 2009 at 14:48 | #10

    First off I just recently did a 301 redirect, it was the biggest mistake I have ever made. It takes months regain just a portion of the links our old site had. Second it sounds like its a universal nofollow tag. Supposedly no follow tags are only applicable to google and not all the major search engines.

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