The Importance of Canonical URLs for SEO

What is Canonical URL for SEO?

Based on Moz's definition, a canonical tag (aka "rel canonical") is a way of informing search engines that a specific URL represents the master copy of a page. Using the canonical tag prevents problems caused by identical or "duplicate" content appearing on multiple URLs.

It does this by specifying the “canonical URL”, which is the “preferred” choice of a web page – the original source, even. Using it well will certainly improves a site's SEO.

When Should You Apply Canonical URLs?

301 Redirect or Canonical?
You have two choices: One is to perform a 301 redirect and another which is setting canonical URL, which one will you choose?

The answer is simple: just use 301 Redirect unless there are technical reasons not to.

If you can’t redirect because that would harm the user experience or be otherwise problematic, then set a canonical URL.

Should a page have a self-referencing canonical URL?
The answer is YES. Google have confirmed it's best to set this on every page. That’s because most Content Management System (WordPress, Joomla etc.) will allow URL parameters without changing the content. So all of these URLs would show the same content:

http://my sampledomain.com/social-media/websites
http://my sampledomain.com/social-media/websites?cmpgn=instagram
http://my sampledomain.com/social-media/websites?cmpgn=twitter
http://my sampledomain.com/social-media/websites?cmpgn=facebook

In the example above, the (1) domain name is the canonical URL while the rest are duplicate copies of the same article copied form (1). By inserting the rel=canonical tag this tells the search engines to pass any link juice from the duplicate page to the original page. This way, you can keep both versions of the page live, but your SEO doesn't take a hit. This also works for Cross-Domain Canonical Domains e.g. domainB.com (duplicate) → domainA.com (primary source)

How to Set the Correct Canonical URL

Using the same example domains shown above (1) to (4), we shall choose the (1) domain (the original version) as the canonical URL while the remaining domains (2) to (4) as the sites which will incorporate the canonical tags. Here's the exact code you need to insert for domains (2) to (4)

<link rel="canonical" href="http://my sampledomain.com/social-media/websites" />

Conclusion:

Rel=canonical is a powerful tool in an SEO’s toolbox, but like any power tool, you should use it wisely as it’s easy to cut yourself. For larger sites, the process of canonicalization can be very important and lead to major SEO improvements.

Updated on: 01/02/2019