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Getting serious about your technical SEO? You may well have come across canonical URLs. In the event of duplicate content, canonical tags can help you present the right version to search engines, so that they know which one to show in the search results. But first, what is a canonical URL, and how do you use a canonical tag? We explain everything in this article.

What is a canonical URL?

You can think of a canonical URL as the main URL; the main version of the webpage that is prioritised by search engines such as Google in the event of duplicates; repetitive content is hardly ideal in the search results. Take this as an example:

  • Canonical URL:
  • Alternate URL:

What is a canonical tag?

A canonical tag (or a rel="canonical" tag) is a snippet of HTML code on a page that signals to the search engine what page to prioritise; canonical tags typically point from an alternate page to the canonical page.

A canonical tag tells the search engine that that’s the page that should be indexed, that’s the page that link authority combined from alternate URLs should apply to, and that’s the page that should, ultimately, be shown in search results.

When should you use a canonical tag?

When to use a canonical tag is something you should know for SEO success. Canonical tags are designed to stop duplicate pages causing a problem; you should use canonical tags whenever the following is necessary:

  • When the same page is available for different countries - such as one for British users, and one for American
  • When pages have filters or listing options applied

Of course, duplicate content isn’t ideal; avoid it where possible, and only use canonical tags when you need to keep the page. Even if you think you don’t have duplicate pages, you may still have duplicate URLs; this is what matters.  

TOP 5 reasons for duplicate pages

Regional variants

As we mentioned earlier, making the same page available in different regions, with differences such as currency, spelling, and language.

Device variants

A URL may adapt to suit the device the user is accessing it on; it may differ between mobile and desktop for example.

Protocol variants

Displaying the same page on HTTP protocol and HTTPS protocol will warrant a canonical tag, as they’ll create alternative URLs.

Site functions

Google defines this as ‘sorting and filtering functions of a category page’.

Accidental variants

Accidental variants are created when, say, the demonstration page is accidentally left live by developers once they’ve finished working on the site.

How to implement canonical tags

If you’re familiar with HTML, you can add rel="canonical" tags to the <head> section of the page. However, the Content Management System (CMS) of your website may allow you to specify canonical tags without delving into the technical workings of your HTML. For example, Wix, Magento 1, Magento 2, and WordPress all make it easy via their CMS, or through a CMS plugin.

How are signals used by Google?

When Google comes across pages and URLs that are similar, or the primary content is the same, it selects one based on certain signals that the indexing process has picked up on that identifies one as the page to prioritise in the SERPs. The page it chooses will then be crawled most regularly, so as not to use up the precious ‘crawl budget’ that sites have allocated to them.

You can indicate to Google which page to prioritise through a canonical tag, but it may still choose another from the duplicate ‘cluster’ if it seems it to be more ‘complete’. Each cluster of duplicate pages has one single canonical.

The other pages, which aren’t the canonical page, become ‘alternate versions’, though these may be served in specific circumstances where a user is looking for something that only that page can provide. It can be tempting to ‘noindex’ these pages to stop them appearing in the search results; it may concern you that each one features a keyword, and you’re afraid of cannibalisation in the search results. However, those pages may well fit a fairly niche search query, so it’s in your interest to keep them findable within the SERPs.

What does all this mean for your website?

To sum up what we’ve learned, here are some key takeaways for your website:

  • Some duplicate pages serve as alternate versions - refrain from noindexing them.
  • It’s still possible for alternate web pages to rank for more niche search terms, such as a particular product colour.
  • The main content on your web page is known as the ‘centrepiece’; this is what generally doesn’t change when referring to duplicate and alternate pages.
  • Google picks up on a small amount of signal from every page it crawls.
  • Signals are defined as data that is processed by Google after a page is discovered by their crawlers.
  • Some signals are within the control of the web page publisher, such as the canonical tags that we’ve mentioned.

Need help with your website canonical tags?

While there are many areas of SEO you can tackle yourself, it’s understandable that canonical tags might be a step too far - you’ve got a business to run, after all. In this case, allow us to help; we take a thorough approach to your SEO, so from content to canonical tags, our team has all the know-how we need to send you up to those top spots. Have a chat with us today.

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About Chris Simmons

Chris is our onpage SEO Specialist at 427 Marketing, having joined the team in early 2023. He works with our content team to cover the 4 pillars of SEO; content, onpage SEO, technical SEO and offpage SEO. Prior to joining the 427 Marketing team, Chris spent almost 10 years applying his SEO and content skills across several different industries in marketing agency and inhouse roles including tool hire, auctioneering, health care within the NHS and high end luxury retail in both B2B and B2C capacities. His passion for writing, content, UX, technical and on page SEO has expanded our content offerings, helping provide reliable advice about all things SEO to 427 Marketing.

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