What Are Canonical Tags and Why Use Them?

Canonical Tags have been around for almost 2 years now, but there are still many developers who are either not aware of their existence or they don't understand their practical application. Let's take a look at what they are and why you might benefit from them.

Why should I use Canonical Tags?

When you have multiple URLs that represent a single website page, there is a risk that the search engines will see this as a duplicate content issue. This is a common issue with dynamic websites with multiple paths to product content.  For example, depending on how you arrive at a product page page in a dynamic website, you may end up with URLs that look like:


In addition to the duplicate content issue, the URLs above can end up getting long and ugly. Fortunately the canonical tags can serve the purpose of solving both issues by allowing you to turn the URL into:


Implementing Canonical Tags

The Canonical Tag code must be placed in the header of the page. There are two ways to use the canonical tag; you can use absolute URLs or relative URLs, both of which can be seen below. It is recommended that you use absolute URLs over relative URLs but either should work.

The code for the absolute URL will be:

<link rel="canonical" href="http://www.domain.com/product1.aspx" />

For the relative URL it will be:

<link rel="canonical" href="/product1.aspx" />

Additional Applications

There is yet another reason to consider using canonical tags. When a web page has multiple URLs representing it, the PageRank will likely be split up among the different URLs resulting in a lower PageRank score than the page in question may have actually earned.  The canonical tag will help Google understand that the "link juice" should be focused on the URL specified in the canonical tag instead of being split up and should help minimize a loss in the PageRank score.

To be continued...

Stop back again later this week where I will post part 2 of my post about canonical tags.  I will be focusing on the differences between canonical tags, 301 redirects and standard forwards.  I will also look at when and why to use canonical tags over these other options.

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