What’s a Canonical Tag and How Do You Use it for SEO?

The canonical tag is an important part of technical SEO, but it’s far from the most exciting aspect of it. Nonetheless, understanding how to use the canonical tag correctly will allow you to improve your performance in the SERPs and prevent major ranking issues.

In this post, we’ll cover the canonical tag, what it is and what the best practices are for using them.

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Why it’s important

Even though it may seem like a simple HTML tag, knowing how to use them correctly and when to use them is quite a complex topic. Understanding what canonical tags are and what some of the best practices are for using them will help you to improve your SEO efforts or better understand SEO work done by third parties.

What is a canonical tag?

A canonical tag is an HTML tag that tells search engines what the original version of a page is. This can help prevent duplicate content issues in the case of multiple pages with the same content on them by clearly signalling which page is the “preferred” version.

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In the absence of canonical tags, search engines like Google will choose which version of a page is the preferred version. This usually happens when there are multiple pages with the same (or nearly the same) content on them. This may lead to Google choosing the wrong version, or even multiple pages on the same site competing for the same keyword.

A canonical tag allows you to specify the preferred version, helping search engines to select the right version to show in the SERPs.

Why are canonical tags important for SEO?

Duplicate or low-quality content can prevent your site from ranking well, especially if a large portion of your website consists of duplicates. This causes Google to spend resources crawling low-quality pages, wasting your crawl budget and potentially causing index bloat.

Canonical tags can prevent this wasted effort and clearly indicates what the preferred version of a page is, ensuring resources are focused on the most important pages. This helps boost your rankings and allows pages to be indexed more quickly.

Another important reason for using canonical tags is to avoid your content being stolen. Although it’s becoming less common, scraping sites do still exist. These sites can instantly copy content from a site and try to get it indexed before the original, potentially leading to the original (your page) being seen as a duplicate by Google.

Although other strategies may need to be used to prevent this, using the correct canonicalization strategy will work to reduce the issues that automated scraping can cause.

When should I use a canonical tag for SEO?

A canonical tag can be used on all pages and can point to any page on your website. In general, it’s advised to use the canonical tag on all pages that can be accessed by search engines. If multiple pages contain the same content, picking the preferred version and adding a canonical tag on all pages pointing to the preferred version is ideal.

If the page is unique, adding a canonical tag pointing to itself, also called a self-referencing canonical tag, is considered best practice.

Best practices

Even though it’s just a single HTML tag, there is a lot to say about canonical tags. Although we can’t cover everything in a single blog post, below are some of the most important canonical tag best practices to give you a better understanding of how canonical tags work.

Use the complete, correct URLs in your canonical tags

Always use the complete URL in a canonical tag, and always make sure the URL is the correct, preferred version. If your page is https://mysite.co.uk/page1 then the canonical tag should link to exactly this page, not to http://mysite.co.uk/page1 or http://www.mysite.co.uk/page1.

Use a single canonical tag per page

Even though this seems like common sense – it’s not like a site can have multiple original versions of the same page – it’s more common than you might think for sites to have multiple canonical tags. Extra plugins or a new developer may accidentally add an extra canonical tag, confusing search engines and potentially causing ranking issues.

Always use canonical tags on existing pages

Even if the page is unique and there are no duplicates, you should still add a self-referencing canonical tag to the page to send a clear signal that the page is the original.

If there are more than two duplicates, point all canonical tags to the same version

When you have three pages with (nearly) identical content, then it’s important that all of the canonical tags point to the same preferred version. Say you have three identical pages called page1, page2 and page3. If the preferred version is page1, all three of the pages should have a canonical tag pointing to page1. It’s important to avoid canonicalization chains where page3 points to page2, and then page2 points to page1.

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Don’t go overboard canonicalizing pages (especially when it comes to near-duplicates)

Quite a number of marketers and developers will recommend canonicalizing all pages that look slightly similar, but canonicalizing too many pages can cause crawling issues. Paginated pages is a good example of this since canonicalizing all of these pages to the first page will prevent/reduce search engine crawling on the other pages, potentially preventing certain products or articles from being found.

Don’t canonicalize URLs when they should be 301 redirected

If pages add no extra value, it’s often preferred to 301 redirect the page to the preferred version instead of using a canonical tag. When exactly you should pick one over the other is best left for another blog post.

That being said, a 301 removes the duplicate and redirects both search engines and users to the preferred version, also resulting in the consolidation of ranking signals.

On contrary, a canonical tag will tell search engines that a page is a duplicate of another page, but the page will still be accessible to users.

Conclusion

Canonical tags are a complex subject, especially if SEO isn’t your core business. That being said, we hope that this post has helped you to understand why canonical tags are important and when you should use them.

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