How to use the canonical tag

The canonical tag is something we’ve discussed on many occasions, but not in an explicit way. This post will help you understand how to use the canonical tag and – more importantly – why you should use it.

What is the canonical tag

The canonical tag is a html attribute created by Google to help webmasters manage duplicate content. By choosing the original version of the content the tag allows a webmaster to say to “ignore this page, it’s a duplicate. This is the original version!”

In some senses, an easy way to think of the tag is as a reference or a citation.

How to use the canonical tag

Thanks to modern semantics, the canonical tag is incredibly easy to use – it’s just one line of code:

<link rel="canonical" href="http://domain/url" />

See? That small line of text is extremely powerful, so there is a risk involved with using it because it does exactly as it’s told, so a small mistake can be devastating (as reported by SEOmoz here).

Why you should use the canonical tag

The canonical tag is majorly important in any webmasters toolkit – it’s up there with meta robots and 301 redirects . Without it, there would be no easy way to manage duplicate content and, as we all know, duplicate content will only result in one thing: penalisation.

The perfect example of when the tag should be used is e-commerce. E-commerce sites by their nature are built for products and categories. Unfortunately, sometimes products do not fit into just one category so there could be more than one URL for the same product. By choosing a “canonical” version of the product (perhaps the one with the highest search volume/click through rate) you will remove the risk of penalisation for duplicate content.

Written by Jason John Mills