What is URL Canonicalization in SEO?

URL Canonicalization is an elegant way to solve the problem of duplicate content, which can cause a lot of issues in search engine optimization and lead to low ranking in search results.

Here’s the complete guide about URL Canonicalization in SEO. In this article, we talk about :

  • What is URL canonicalization ?
  • Why do you need URL Canonicalization?
  • What are the best practices for Canonicalization?
  • What is the difference between URL Canonicalization and URL Redirects?



What is URL Canonicalization?

Sometimes, your site may have duplicate content or identical pages on it. URL Canonicalization is a way to tell search engines which URL represents the original copy of your content. You can do this by adding a canonical tag (also known as rel=”canonical”) tag in your pages. A canonical tag refers to the original copy of your content (called canonical URL). When you add the same canonical tag to a group of duplicate or identical pages, it helps the search engines understand which of them is the original copy.

Even if your duplicate content is crawled and indexed, only its canonical URL will be displayed in the search results. Basically, the canonical tag tells search engines which URL you want to show in search results.

Here’s an example of canonical tag syntax for reference. Notice how its href attribute points the canonical URL.

canonical tag example

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Why do you need URL Canonicalization?

Duplicate or identical content can pose many problems that hurt your search engine rankings. If search crawlers have to go through lots of duplicate content, they may end up missing some of the unique content on your site. Also, since your backlinks will be scattered across multiple URLs about the same content, it will diminish the ranking ability of your those pages. Even if your content is ranked, search engines may show the wrong URLs in search results. URL Canonicalization makes it easy for search engines to identify your duplicate content and rank the right page.

You must be wondering why anyone would create duplicate content on their site. The problem is that search engines view web pages differently than the way we do. They view each URL as a separate page. For example, the following URLs may load the same page about nike shoes and therefore appear to be the same for a human.




But they’re unique pages for a search engine. This is just a simple example of 3 copies of 1 page. Now imagine the amount duplicate content you may have, if you’re running an e-commerce website with thousands of products, or a blog with hundreds of articles.

Dynamic code driven websites such as modern content management systems (CMS) and blogging platforms only make things worse. They generate dynamic URLs, automatically add tags and provide multiple paths to the same URL. Some of them even add URL parameters for search & sort features.

You may have hundreds of duplicate pages on your site unknowingly & this will hurt your rankings. In fact, even the following URLs of your home page are seen as unique pages by a search engine.





You can also read our list of Off-Page SEO Techniques and On-Page SEO Checklist to boost SEO rankings for your website


What are the Best Practices of URL Canonicalization?

Here are a few important best practices to follow while adding canonical tags to your pages.

1. Canonical Tags can refer to themselves

The canonical tag in the original copy of your content can have a canonical URL pointing to its own URL. For example, if A,B,C are identical pages and B is the original copy, then the canonical tag on page B can have a canonical URL pointing to B.


2. Add Canonical Tags to every page on your website

Add canonical tags to all crawlable pages on your website. You can’t control how people link back to your pages. Canonical tags will help search engines consolidate the backlinks to your content and boost your search rankings.

Learn how to build backlinks to your website. Check out our list of Best backlink checker tools to use for your website.


3. Manually check a few dynamic canonical tags

Most e-commerce websites, blogging platforms and content management systems have modules and plugins to automatically add canonical tags to every page. However, a buggy plugin or module can end up adding wrong canonical tags for all pages on your site. So manually check a few canonical tags to ensure they’re pointing to the right canonical URLs.


4. Avoid Broken links and Canonical Tags with Circular reference

If your canonical tags point to broken links, search engines will avoid them. Also, avoid confusing search engines by adding a circular reference in your canonical tags. For example, if you canonicalize page A -> page B and page B -> page A, then it’s a circular reference and will be ignored.


Bonus Read : Learn everything you need to know about Nofollow links in SEO


5. Be careful about near duplicate pages

When it comes to URL canonicalization, people canonicalize only exact duplicate pages. You can also canonicalize near duplicate pages such as pricing pages with same content but different currencies. However, remember that the non-canonical URLs will not get ranked. Also, if they’re too different, then search engines will ignore their canonical tags.


6. Canonicalize duplicate content across domains

You can also canonicalize duplicate content published across multiple sites by adding canonical tags across those domains, if you control those sites too. For example, if you’re an online publisher who publishes articles on multiple websites, you can canonicalize them. It will help concentrate your ranking power at one site. However, remember that non-canonical sites won’t rank on search engines.


7. Use Canonical Tags for Accelerated Mobile Pages

Google has recently launched the AMP (Accelerated Mobile Pages) Project that allows online publishers to create a separate mobile-optimized version of web pages that loads faster on mobile devices and provides an amazing user experience in Google’s mobile search. However, since AMP HTML pages are basically HTML web pages without javascript, it’s recommended to use canonical tags for AMP pages, so that it is not penalized as duplicate content.


You can also read our Best On-Page Techniques to boost search engine rankings.


What is the difference between URL Canonicalization and URL Redirects?

URL Canonicalization may seem to be same as 301 URL Redirects but they’re not. For example, if you redirect page A to Page B, then visitors will never be able to see what’s on Page A. However, if you add canonical tag from page A to page B, then visitors will be able to see page A and search engines will know which page is the original copy.

So you need to use canonical tags or redirects, based on your situation. If you’re changing domains, or have broken links, or wrong/outdated content then use redirects. In case of similar or duplicate content, use canonical tags.

However, in both cases the link equity is passed to the destination URL whether it’s a canonical URL or redirected URL.


You can also read How to Create SEO-Friendly URL Structure to optimize URLs for SEO


What do you think? Have you used canonical tags on your website? Did it improve or lower your rankings?