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Understanding Canonical URLs

If your website contains any single pages that may be viewed under multiple URLs, or different pages that have very similar content, Google will see these as duplicate versions of the same page. Potentially this may be seen as a method of flooding the search results with similar content, so Google will choose one URL as the canonical or primary version and index that one, with all other URLs being considered as duplicate and either ignored or crawled less often. So why is this important for your SEO efforts?

If Google identifies URLs on your site as duplicates it will automatically decide which page to take as the canonical version, unless you explicitly tell Google which one to use through the use of a canonical tag. One version of your pages may be the main one you would want people to find from a Google search, and so it makes sense to control how Google may index your pages and target the preferred version, rather than the one that you ideally don’t want to be found.

Canonical pages can often be a problem for e-commerce stores, where the same product pages may be shown under different categories, so that essentially the same page can use different URLs. The canonical URL can be the page that Google thinks is most representative from a set of duplicate pages, such as yourdomain.com?dress=1234 and yourdomain.com/dresses/1234. It should be noted that the pages do not need to be absolutely identical, so that minor changes such as sorting products by price or filtering by item colour under different URLs do not make the page unique. Also, the canonical page can be under a different domain than a duplicate.

Therefore as the website owner or marketer, you should be aware of this possibility and use canonical URLs to control which version of the duplicate pages Google will index and therefore display in the search results. This is because some pages may have a stronger position in your site’s hierarchy to help it rank better, or it will give a new visitor to your site a better landing page experience once they arrive from the search results.

If you have a Search Console account set up for your website, you can use the URL Inspection tool to learn which page Google considers canonical. Even though you may specify one page as the canonical it should be noted that Google might choose a different canonical for various reasons, such as performance or content. For example, the search result will probably point to the mobile page if the user is on a mobile device, even if the desktop page is marked as canonical.

The main methods used to denote the canonical URLs are to either use the rel=”canonical” link tag in the head code (probably the most common method), to use the rel=”canonical” HTTP header, or to use a sitemap. One other method is to use 301 redirects for retired URLs, but this is a slightly different approach. Google provides more information about canonical pages and the pros and cons of the ways to specify a page in this article.

If you have any questions about canonical pages and how you should be using them for your website, please get in touch.