Handle duplicate content indexing for SEO with the rel=”canonical” attribute

For anyone focusing on SEO and duplicate content indexing, i.e. the same page indexed with several URLs, thus having a negative page rank impact, Google, Yahoo and Microsoft now all support the canonical relation on link elements.


It is outlined more in detail in Google’s blog post Specify your canonical, but the gist of it is that a page of yours could be indexed with many different URLs. I.e:


http://robertnyman.com/2008/05/27/the-ultimate-getelementsbyclassname-anno-2008/ (Note: www omitted)

http://www.robertnyman.com/?p=761 (Note: WordPress nowadays redirects these sort of URLs)

What you want is to have just one URL for a page indexed by various search engines, to help it getter a higher ranking and only publicly promote that URL.

The rel="canonical"

The three major search engine players have announced that they now support a new rel attribute on link elements, displaying what is the preferred URL for the currently viewed content. Therefore, if I were to prefer the first of the above listed URLs for my post, I could add a new element to that page, looking like this:

<link rel="canonical"

What’s good

Naturally, anyone working with or stumbling across any SEO strategy will definitely appreciate such an approach to actively promote the URL one wants to for a page, instead of people linking with different links to the same content.

It’s also good that all three of Google, Yahoo and Microsoft support this, because it adds a wider meaning to it.

Another upside is, the perhaps given, answer by Google that the rel="canonical" is regarded as a strongly honored hint, rather than an actual directive. If it had been a directive, I’m sure it would’ve been fairly abused instantly.

What’s maybe not so good

An interesting reply from Google is that the rel="canonical" can point to a redirecting URL (but only on the same domain). I’m not sure about this, but it sounds like a possible opening for redirecting URLs to something completely different, enhancing something which maybe doesn’t deserve as much attention. Sure, all search engines must validate this, but I’m sure there will be arguing about old content having been updated, extremely extensive algorithms trying to take such factors into account etc.

Maybe I’m completely wrong here, but that thing in conjunction with people who will definitely trying their hardest to misuse this, I have an ominous feeling.

Another interesting aspect is mentioned by Anne in rel=”canonical”, and that is that this is implemented out of any standardization process or registry. But hey, if you’re big enough, you do something and other have to follow, right? Sometimes such behavior results in great things, and other times not so wonderful consequences…

Adding this to your web site

If you use WordPress, which a lot of people seem to do, or Drupal, Joost de Valk has released solutions for. Please read more in Canonical URL links if this sounds interesting (Disclaimer: I have not tested these myself).

Posted in Developing,Google,Technology |

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