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When someone speaks of setting up canonical tags, it essentially means using the rel attribute equal to canonical , as well as the href attribute with the value equal to the URL in the section of the link tag. 

The source code looks like this:

																			
																			https://seranking.com/
																		
																		" />
																	

Hence, canonical is not a tag but the value of the rel attribute, and its purpose is to make it clear to the search engines which version of the page they should rank.

What should you use canonical for?

Canonical is used for some URLs when the site has a main version of the document along with other, additional documents with similar content. What canonical does is point the search engines to the main version of the page.

Pay special attention to the word “similar”—we will come back to this definition later.

Here’s what Google Help has to say about canonical:

If you have a single page accessible by multiple URLs, or different pages with similar content (for example, a page with both a mobile and a desktop version), Google sees these as duplicate versions of the same page. Google will choose one URL as the canonical version and crawl that, and all other URLs will be considered duplicate URLs and crawled less often. 

If you don’t explicitly tell Google which URL is canonical, Google will make the choice for you, or might consider them both of equal weight, which might lead to unwanted behavior.

How can canonical URLs be specified?

There are several ways to specify the main version of a page. All of them are described in more detail in Google Help . The most common way is to use the tag—and we will use it in the examples. Other possible options include:

• The tag with the rel=”canonical” attribute
• The Rel=”canonical” HTTP header
• A Sitemap file

As an alternative to canonical , you can also use 301 redirects , but keep in mind that redirects function entirely differently as they make only one version of the page available to search engines and users. Therefore, choose the method accordingly to the results you expect.

Best practices of using Canonical

Canonical is normally used to avoid similar or duplicate content appearing in search results. We will discuss below why the content can be duplicated.

Important! Using rel=”canonical” href=”” /; does not prevent search bots from indexing and crawling the document. Canonical is a recommendation and may be ignored by the search engine. Canonical indicates which version of the document should appear in the search results and which, in your opinion, is the main one.

If you want to block indexation, use the following:

• X-Robots-Tag: noindex HTTP header

Read more in Google Help .

Why it’s considered good to use Canonical

The use of canonical has been recognised as a helpful practice. It is implemented to prevent potential duplicate content issues, even if there’s no hint of duplicate or similar content.

It’s considered good practice to put canonical for each major page version, whether they have duplicate or similar content or not, and point it to that very same page.

Technically speaking, the page https://seranking.com/subscription.html has this canonical :

																			
																			https://seranking.com/subscription.html
																		
																		" /> 
																	

Here, the value of the href attribute of the link tag contains the URL of the page where this link tag is located.

This solution helps you avoid possible problems and does not allow you to assign any parameters to the page and index pages with additional parameters.

Sorting options

The classic use of canonical is to specify the main document when using filtering, sorting, and other actions that result in a URL change.

Let’s see the laptop category on ebay as an example: 

https://www.ebay.com/b/Workstation-Laptops-Netbooks/175672/bn_7116632031.

This is the main category that contains laptops for work and is optimized for this keyword cluster. Canonical for this page looks like this:

																		
																		https://www.ebay.com/b/Workstation-Laptops-Netbooks/175672/bn_7116632031
																	
																	" /> 
																

The page is pointing to itself.

The page contains classic navigational elements:

• sorting by parameters
• changing the view type

Let’s change the view type. Products are now shown in a column:

But what matters the most for SEO specialists is the changed URL. Now it looks like this: https://www.ebay.com/b/Workstation-Laptops-Netbooks/175672/bn_7116632031?rt=nc&_dmd=1.

Notice the parameters that appear at the end of the URL. Sorting options or other actions are implemented using these parameters. An infinite number of such pages can be generated depending on the possible sorting options. And from a search engine’s point of view, each variation with a new parameter is a separate URL.

If such pages end up in the index, pages with the same or very similar content—and most likely with the same

It is to prevent such problems that you need to use canonical —it allows you to indicate the main version of the document that you want to see in the SERP. In the example, the sorting page has the following canonical :

																	
																	https://www.ebay.com/b/Workstation-Laptops-Netbooks/175672/bn_7116632031
																
																" /> 
															

That is, the page points to the main version of the document without parameters .

Unoptimized filtering

When a variety of filtering parameters are applied, an online store website can have many pages created that are not optimized for any keyword cluster.

When we talk about optimization for a keyword cluster, we mean that the document has:

• a