How to use Canonical Tags

January 17, 2015

Angie Stewart, Online Marketing Consultant for Maginus, working as part of Maginus’ Online Marketing Agency has written this guest blog post on the best use of Canonical Tags. It’s often misunderstood, even in the SEO business but can help you take control of your website.

How to Use Canonical Tags:

Take Control and Clean Up Duplicate Content

What is a Canonical Link Tag?

When you hear the words ‘canonical element’, ‘canonical tag’, ‘canonical URL tag’, ‘rel canonical’, ‘rel=canonical’ and last but not least ‘canonical link tag’, relax, these all refer to the same function.

When multiple ULS’s exist that display the same content, the ‘canonical link tag’ is located in the head section of a webpage indicating to search engines the canonical or ideal page which should be displayed.

When would you use a canonical tag?

Canonical Link Tags are a great way to enforce order and consistency when duplicate content issues arise. When content is identical or very similar – it may present itself on various pages and be accessible through numerous, different URLs .

Duplicate content can occur for the following reasons:

Duplicate content caused by filtering

Duplication is often caused by filtering products within a website. i.e.

This page displays a write up about French wines and a list of French wines available for sale. It also allows me to filter by price range, colour and vintage of the wine I desire.

When I filter, I get a URL, such as:

Effectively, this is the same page, the write up about French wines is still the same, the only difference is that the selection of wines displayed as been reduced to match my filter.

Because they have two separate URL’s they will be seen as separate pages by Google and other search engines.

Duplicate content caused by URL parameters, like session IDs or tracking IDs

Tracking parameters exist to identify the different sauces through which traffic is driven to a given page. Session Ids exist to identify a specific user. Whilst both are extremely useful, they can cause duplicate content.

Again as explained above, the outcome is the same content identified via different URLs.

In both instances using a Canonical Link Tag is a simple and quick means of indicating which URL is the primary, most important or preferred URL.

Why should you care?

So you understand what a canonical is and when it should be implemented, but how and why is this really going to help you and your site?

The answer is this; duplicate content can negatively affect your website in the following ways:

  • Reduced Crawling & Indexing. Search engine crawlers have a limited bandwidth on each site (based on numerous factors). If the crawler is able to crawl 100 pages of your site in a visit, you want it to be 100 unique pages, not 100 of which only 10 will make the search results.
  • Reduced ‘Link-Juice’. If a page has 10 possible URLs, then those 10 URLs might all have external links pointing to them. You want all that ‘link-juice’ going to your ‘canonical page’. By using the canonical command, links to all URLs will be consolidated to the one specified as canonical.

How is the canonical link tag implemented?

A canonical link tag can be implemented in the header of the HTML website.

  • Make sure to URLs are “standardised” or “normalised” and consistent in the navigational journey.
  • Adjust your content management system to indicate only the URLs you want.
  • Once you’ve picked your ideal / ‘canonical’ URL make sure you are consistent with your internal linking so that they lead to the same site.

In the head of all non-priority pages, simply, add a tag to specify the version of URL you want to prioritise e.g.

<link rel=”canonical” href= “”/>

One Final Note

I often get asked the following questions regarding canonical tags:

1. Can a canonical page be redirected?
A canonical page can be redirected if necessary and Google state that if this occurs they will process the redirect as usual and try to index it.
2. Can a canonical tag be used to suggest a preferred page on a different domain?
This is a good question, mostly because this has changed since the implementation of the canonical tag. Originally the answer was no, but in December 2013, Google announced they support cross-domain canonical tag use.

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