Why put rel=canonical to the same url ?

[Tintanus]

Hi all. I've heard that it's good to put the link rel canonical in your header even when there is no other important or prefered version of that url.

If you take a look at moz.com and see the code, you'll see that they put the <link rel="<a class="attribute-value">canonical</a>" href="http://moz.com" /> ... pointing at the same url !

But if you go to http://moz.com/products/pricing for example, they have no canonical there !

WHY ?

Thanks in advance !

[Hutch42]

This is done for pages that may have additional information added to the url in a query string. While I prefer to have all pages canonical to themselves, I highly recommend doing it to any home page or landing page that can have multiple external links pointing to it.

[Anti-Alex]

You generally want canonicals on every page but Google has been paying a little less attention to them lately. They seem to be moving in the multi language direction so canonicals may be switched over to that one day.

Anyway you use them to let Google and most crawlers know which page to index. So if you have a bunch of URLs with different variables, they know to only index the root page.

ie:
http://website.com/page/?var=1
http://website.com/page/?var=2
http://website.com/page/?var=3

Set the canonical to http://website.com/page/, and that'll help let them know to only index http://website.com/page/ - also helps prevent duplicate content issues.

[EricaMcGillivray]

Canonicals on every page is definitely the best practice.

As to the Moz mystery, probably whomever wrote the specs for that page forgot to include canonical tags. Even our SEO is far from perfect.

[Tintanus]

I do appreciate this kind of honesty. For me, honesty is the only thing that has made me have clients for more than 3 years.