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Canonical Tags – Everything you need to know about Canonicalization

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Canonical (rel=canonical) – We have often heard this term in on-page SEO. But to know more about it, let us discuss the canonical tag and its application in SEO.

Let us take an example of a website that sells Mobile Phones which has different pages with the same content. Therefore, it might have different URLs for the same page such as

  • smartphone.com/apple
  • smartphone.com/brand/apple
  • smartphone.com/apple/utm_campaign

All the three pages have similar content or are exact replicas of each other. Such pages may be created due to some changes in the backend. These URLs could be used for tracking purposes or created due to different categories in the top navigation.

However, having so many URLs for the same page can leave Google incredibly confused about which URL to rank in the SERP.

(Depending on the signals, Google picks up one URL that it feels is the best version and ranks it.)

Google is not always accurate and might end up choosing the incorrect URL. This makes it necessary to let Google understand which page and URL to rank in the SERP and which to ignore. Here is where canonical tags come in the picture.

What are canonical tags?

A canonical tag (rel = canonical) in SEO is a piece of HTML code that helps Google to rank a particular page from a group of similar/duplicate pages.

Let us follow our previous example of a website selling mobile phones to further elaborate on the term. Suppose you want to indicate Google that “smartphone.com/apple” is your main page which you want to rank for. You will simply put a canonical tag on all the other duplicate pages.

Why are canonical tags important in SEO optimization?

Whether you are an SEO agency or an SEO professional, canonicalization should be on your list of activities within On Page SEO optimization. Now, let us find out what makes canonical tags so important in SEO?

  • Saves crawl budget

By specifying a canonical tag, you indicate Google which URL to index and rank out of various versions of the page. This saves valuable time for the spider that crawls your website. The crawler, also known as web spider, need not waste time crawling pages that have been canonicalized. In this way, the web spider can reach other important URLs and content on your website and saves your crawl budget. 

  • Proper allocation of Link Juice

Using canonical tags ensures that the link juice is passed to the correct version of the page. If you have different pages with similar content, Google evenly distributes link juice to all these pages. By specifying a canonical tag, you let Google decide the page you want to give importance and rank in SERP. Google then passes all the link juice to the important page, ignoring all the duplicate pages. This ensures that there is a proper allocation of link juice on your website.

  • Ensures relevant URLs rank for queries

Canonical tags help ensure that relevant URLs rank for keywords. The last thing you want is two URLs of your website competing against each other for the same keyword on SERPs. By using rel=canonical, you can avoid this situation. Make sure you specify the proper canonical URL that you want Google to index and rank in the canonical tag HTML code.

  • Canonical tags make Google’s job easy

If you have a huge website with numerous URLs, it becomes tedious for Google to crawl all these URLs. When coupled with the confusion of duplicate pages and different variations of the same page, Google will have a hard time crawling and indexing these URLs. But, it is your website that will suffer the consequences. So, in order to make Google’s job easy, you need to specify proper canonical tags on all the pages. This makes sure Google crawls and indexes the correct pages.

Canonical Tag Syntax

The syntax of Canonical Tag is <link rel=“canonical” href=“URL” />

The code has two important components

  1. rel=”canonical” 
  2. href=”URL”

link rel=”canonical”

rel means relationship. Therefore, we define the relationship of the link as canonical.

href = “URL”

href tells the link’s destination. Here is where you put the URL that you want Google to index and rank. This is also called the canonical URL.

Coming back to our example, our smartphone website has the following URLs

  • smartphone.com/apple
  • smartphone.com/brand/apple
  • smartphone.com/apple/utm_campaign

You want Google to only index and rank “smartphone.com/apple” out of these URLs. All you must do is put a canonical tag on the duplicate pages.

This means you put a canonical tag on both URLs 

“smartphone.com/brand/apple” and “smartphone.com/apple/utm_campaign”. 

The canonical tag will be as follows

<link rel=“canonical” href=“https://smartphone.com/apple/” />

Simple. This tells Google that “smartphone.com/apple” is your main version and it should index and rank it, ignoring the other duplicate pages.

Note: The canonical tag should always be placed in the <head> section of the page.

What is a self-referential canonical tag?

A self-referential canonical tag is a tag that is defined on the main version of the page; irrespective of duplicate pages elsewhere.

This means, even if your page does not have other similar pages with duplicate content, you still put a canonical tag on that page. This is also known as self canonical.

  • Example of self canonical

Let us take our website selling mobile phones for instance. 

A self-referential (aka self-referencing) tag refers to adding a canonical tag to the main page “smartphone.com/apple”. You can add this canonical tag even if there are no other duplicate pages of this URL (i.e. “smartphone.com/brand/apple” and “smartphone.com/apple/utm_campaign” do not exist).

“smartphone.com/apple” page will have a self canonical tag as follows:

<link rel=“canonical” href=“https://smartphone.com/apple/” />

The syntax for self-referential canonical tag is the same. The only difference between the two is that a self-referential tag is placed within the head section of the main page.

  • Google on self-referencing canonicals

In one of his webmaster hangout sessions, Google’s John Mueller said that Google recommends putting self-referential canonical tags on all pages. He pointed out that sometimes many different variations of URLs get created due to a mixture of upper and lower case or www and non-www variants. 

However, using self-referencing canonicals directs Google towards the proper URL to index and rank.

Hence, adding self-referential canonical tags on all the pages is now considered as a best practice in SEO.

What is a cross-domain canonical tag?

A canonical tag given on a page that is not on your domain, but has content similar to a page on your website, is called a cross-domain canonical tag.

For example, you have a blog page “abc.com”. You decide to syndicate your blog articles. Syndicating basically means re-posting your blog posts on other domains as a guest. The purpose of this process is to share your content on popular websites to increase your reach. 

But one problem that occurs in this process is that the same content which is on your website is used on other websites. This could lead to Google flagging it as a duplicate content. In order to avoid this scenario, we use the cross-domain canonical tag.

If you have re-published your article on a popular website like Medium, this page should have a cross-domain canonical tag stating that the main version of the page comes from abc.com.

The cross-domain canonical tag will be as follows

<link rel=“canonical” href=“https://abc.com/article” />

This measure tells Google that the main article is on abc.com and has been re-published on Medium.

The syntax for cross-domain canonical tag is the same. The difference here is that this canonical tag is added to the page where you have re-published your content. This measure is called cross-domain as you are putting a canonical tag on a page that is not on your domain.

Note: All the syndication websites might not include a cross-domain canonical tag, despite multiple requests. You must play the risk game in these situations.

How to audit canonical tags and issues on a website?

  • Manual checks

If you have a small website and want to manually check the presence of a proper canonical tag on your pages, perform a manual check. Follow the steps mentioned below to do the same:

  1. Go to your page 
  2. Press Ctrl+U to view the source code of the page
  3. Search for “canonical”
  4. You can find the canonical tag code in the <head> section
  5. Make sure the canonical tag is implemented correctly
  • Using Tools

Checking manually becomes tedious if you have a huge number of pages on your website. For this, you can utilize various crawling tools for checking canonical tag implementation.

Ahrefs has its own site audit tool which gives you all the information you need about canonical tags on your website.

You can also use Screaming Frog for auditing canonical tags which is much more detailed and resourceful. Just open the Screaming Frog Spider software and make sure you check “canonicals” in the Crawl settings. Once the crawl is complete, you can view all the details under “Canonicals” tabs. 


Canonical tag is a very important part of code in relation to on-page SEO techniques. Google has stated multiple times that it encourages the use of canonical tags on all the pages.

However, you need to avoid the presence of duplicate content on your websites as much as possible. But we do understand that for large websites, sometimes doing so is difficult. Hence, duplicate pages are created due to various reasons.

We advise you to use proper canonicals on all pages with different versions and duplicate content. The best practice would be to make sure that you put a self-referential tag on all your pages to avoid confusion.

The canonical tag is just a simple one-line code, but it works wonders.

Let us know in the comments section if you have faced any such canonicalization issues and how have you dealt with them. Also, let us know if you have any doubts regarding canonical tags.

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