The Quick Answer: A canonical tag is a line of code within the backend of a page that tells search engines which page you want to be indexed when multiple versions exist across different URLs.

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The Canonical Tag Was Announced February 2009.

Google announced the launch of the canonical tag on its official blog on February 12th, 2009. They further explain the value of a canonical tag is to tell search engines which version of a URL is the one it should index and include in its search rankings. While Google highly encourages the use of the canonical tag, it is not a directive that they must comply with.  In many instances, if Googlebot (Google’s search spider) identifies a canonical other then what’s provided, it reserves the right to self determine the correct (best) canonical URL.


What’s The HTML Code For the Canonical Tag?

<link rel=”canonical” href=”” />

the canonical tag can be on pages where the canonical value is self-referencing (matching) or referencing a different URL.  Two examples:

  1. <link rel=”canonical” href=”” /> This is the canonical value for this blog post and correctly self references its own URL as the canonical version Google should include within its search engine.
  2. <link rel=”canonical” href=”” /> This same canonical tag code must be located on this exact same blog post when tagged with UTM parameters.  For instance, when linked from my SEO newsletter the published URL looks like this. <link rel=”canonical” .

Despite having a valid purpose, we do not want Google to index both versions of this blog post. This is why we include the canonical tag on both URLs pointing to the single “canonical” version of the URL.

When To Avoid Canonical Tags

The only time you need to be concerned about having canonical tags on a page is when you are implicitly blocking it from search engines with a meta robots no-index directive. In this specific instance,  you can confuse Google by giving them two competing directives.  If you have a no-index tag implemented, best practice is to not have a canonical tag regardless if it self references or not.


How Can I Find The Canonical Tag?

All canonical tags can be found within the source code of an individual page.  Simply right click and click “view source”. At that point, you can do a quick search and find “canonical” which will display the canonical code.

Sound like too much work? You can download the Inspect Canonical Google Chrome extension which outlines the value of a page’s canonical and if it presents any SEO risks.