What is Canonicalization in SEO?
by Julie Weishaar
January 14, 2023
What is Canonicalization in SEO

Canonicalization is the process of labeling a webpage so that search engines can recognize it as the original copy of various other duplicate pages and URLs on the internet.

Have you ever searched for your website using the site:www.domain.com sequence?

The result can sometimes be confusing due to different variables of the same web page being shown.

Let’s say you input site:www.domain.com into Google’s search box. You are likely to get results like:

  • domain.com
  • com
  • http://domain.com
  • https://domain.com
  • http://www.domain.com
  • https://www.domain.com

Another common variable for blog posts often looks like this:

  • blog.com/index.php/%postname%/
  • blog.com/index.php/sample-post/
  • blog.com/index.php/2015/01/sample-post/

These URLs have the same destination, header, footer, and even 100% of the same content.

Thus, you could say domain.com is the same as www.domain.com.

However, search engines treat each URL differently. A URL starting with “HTTPS” differs from another URL of the same domain name starting with “HTTP”.

Likewise, www.domain.com is not the same as domain.com to Google.

Think of these URL duplicates as filler content often used to make up for word count when writing essays in college.

Too much fluff will cloud the main essay points your teacher is supposed to focus on, rendering it useless.

Search engines have the habit of crawling web pages before choosing the ones to index.

Different duplicates of the same page will severely impact a website’s crawl budget and possibly affect its position on SERP.

To avoid this, Google and other search engines will automatically choose one of these duplicate URLs as the original copy and prioritize it above the rest. This is known as canonicalization.

However, letting search engines automatically canonicalize your URLs or pages might not be a good idea for reasons such as incorrect canonicalization.

Most tech geeks will manually add a line of code or use the help of plugins if the website is CMS based.

What About Near-Duplicate Pages?

Aside from duplicate URLs, there is also the possibility of having several near-duplicate pages.

This is a common problem with CMS and e-commerce websites.

On e-commerce websites, more than 100 product pages can have almost 90% similarity in content.

This is common when marketing products in the same category on different pages.

For example, online stores that sell Apple mobile devices will have to create a separate page for each iOS version.

The only possible difference between these pages will be the image used, a few personalized texts, and maybe color.

These near-duplicate pages will make it difficult for search engines to index your online store properly and indirectly affect your SEO status.

To prevent this, most businesses designate a single page to highlight all products in the same category. Then, they show it to Google as the primary copy via canonicalization.

Through internal linking, users can then access these products individually.

How Does Canonicalization Affect SEO?

Search Engine Optimization (SEO) is now widespread among website owners.

And the goal is to increase unpaid traffic to your business through improved visibility on the SERP.

But having duplicate pages or URL clones on your website can affect its SEO and impact the traffic it gets. This is precisely why you need canonicalization.

Canonicalization Reduces the Crawl Budget of Your Website

A crawl budget means the number of pages search engines will crawl on your website within a specified time.

For smaller websites, Google might crawl six pages per day. In larger websites like Amazon, search engines might crawl as much as half a million pages per day or more.

The problem is that the more pages you have, the slower it is for search engines to crawl your entire website.

To prevent this, Google will purposely avoid duplicate content. That includes the possibility of neglecting your priority pages.

Using canonical tags, however, will tell search engines which page or URL you want them to focus on when crawling.

In turn, your website’s crawl budget is reduced, and more resources are focused on indexing the priority pages.

It Improves Your Position on SERP

While canonicalization is not as effective as internal linking when it comes to improving rankings on SERP, it is still an essential factor to consider.

Placing a canonical tag on all duplicate pages will signal to search engines that the referenced page deserves more attention.

It is similar to directing Google’s entire focus and resources on a single priority page.

Instead of having all your duplicate pages rank randomly, focusing all the authority on just the original page will give it more chances of competing with other websites for a higher ranking.

How to Canonicalize Your Website?

There are three ways to let search engines distinguish your priority pages from the remaining duplicates.

Using Canonical Tag

The canonical tag method involves inserting an HTML link tag inside the head section of your source code. You need to do this for all the duplicate pages on your website.

For example, if the canonical page is https://www.domain.com, then you need to specify it on every other duplicate page using the link tag below:

<link rel=”canonical” ahref=”https://www.domain.com”>

Using HTTP Header

If you have access to your website’s server, you can use the HTTP Header.

The benefit of doing this is that you can canonicalize URLs for non-HTML pages like PDFs.

The downside? It is only available for web searches on search engines like Google.

Using a Sitemap

Create canonical URLs for all the priority pages on your website and insert them in the sitemap.

Google and other search engines will naturally focus more on these canonicalized pages and index them.

It is, however, important not to include zero-priority pages in the sitemap.

Read more SEO-related content:


Thanks to the rapidly growing digital market, online businesses face more intense competition to rank on the front page of every search engine.

To better optimize your website and generate maximum organic traffic, you need to choose the pages you want to rank for and canonicalize them.

Originally published July 10, 2022, republished January 14, 2023, for added text.

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  1. Paul Lamont

    I have gone back and forth on how to accomplish this in the past. This post is very helpful in making a decision.

    • Julie Weishaar

      Hi Paul, Thanks for stopping by. I am glad the post was helpful to you 🙂

  2. Ryan Biddulph

    Good to know Julie. Sometimes we become overzealous and drop the same keywords in multiple posts. Letting go old posts by deleting all together or simply changing keywords, editing and updating seems to do the trick. Great reminder here.

    • Julie Weishaar

      Hi Ryan,

      I often try to update old posts – it’s a process that keeps our content relevant and can only help.


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