Canonical Tag


Multiple identical or very similar pages on your website (internal duplication) or on its domains (external duplication) can hurt your SEO. Search engines have finite indexing capacity, and they cannot be expected to scan every page created by website owners. They only display a limited number of links in SERPs, so if you create too many duplicates, your most important pages may not get featured in the search dropdown.  

In some cases, duplicate content is part of a company’s marketing strategy. Let’s say a brand launches domains for the US, Canada, and Australia with almost identical service descriptions on three regional websites. If search bots scan all three versions, chances are that some pages will not get indexed, or potential clients may be misled with outdated descriptions in SERPs. 

Canonical tags offer the optimal solution for managing duplicate pages. If the company’s US domain is the main one, it can canonicalize its US pages to show search bots that those pages take priority over duplicates. 

What is a Canonical Tag?

A canonical tag is a code element that directs search robots to the primary version of your content. To tag US pages as separate from Canadian and Australian pages, the webmaster simply needs to add rel=”canonical” to the <head> sections or HTTP headers of secondary pages. 

Here is how to adjust the HTML code of .ca and .au pages:


<link rel=”canonical” href=”” />


Or you can add Link: <>; rel=”canonical” to HTTP headers. 

If a bot visits the .ca and .au pages, it will proceed to rather than indexing the current location. 

When viewing your pages, human users will not know whether they are canonical or secondary. To find out, they would need to check HTML or HTTP. 

Be aware that rel=”canonical” does not prohibit search engines from viewing your secondary pages. It is a suggestion, not a directive. A bot will index your duplicated content if necessary, but search engines try to accomodate website owners and respect their SEO signals.

Canonical Tag

When is a Canonical Tag Useful for SEO?

There are few situations where a canonical tag would negatively affect your SEO. Whether a page tags itself or its internal/external duplicate, canonicalization does no harm. Let’s consider cases where canonicalization may boost your SEO performance: 

  • Self-referencing shows search engines that there is a single version of the page on the web, so there is no point in looking for duplicates, and a bot can index it; 
  • Query parameters are used in a URL, which may result in duplicate creation. For example,  and are two different URLs, even though they lead to the same page and differ only in the order of query parameters. 
  • Near duplicate pages are common for online retail stores. A canonical page can be tagged by pages,, etc. of products that differ by color. 
  • Companies often create personalized landing pages to target narrow audiences. 
  • It may be necessary to launch multiple versions of the same page to run conversion tests. 
  • To provide flawless design and user experience, brands need to create mobile and desktop versions of their online platforms. Apart from rel=”canonical”, you can use rel=”alternate” so far supported only by Google. Add both to the <head> section in your pages’ HTML.
  • Cross-domain (external) canonicalization is needed in cases where several almost identical domains are created for regional or other purposes. 

If you no longer need some duplicates, make redirects to the major version. This option is particularly feasible if you shift from HTTP to the more secure HTTPS protocol, or provide access to the page via multiple domains with no unique purpose. 

Redirects should supplement rather than replace canonicalization. When used intelligently, both features can benefit SEO performance. If your redirects cease to work for some reason, only the main page versions will be indexed.

What is Canonical Tag

Best Canonicalization Practices

Use the following tips to make the most of rel=”canonical”:

  • Use absolute URLs rather than relative URLs. Specify the protocol and www. to prevent duplication. A single relative web address can lead to four full links that will be perceived by Google as unique virtual locations. 
  • Each page should have a single canonical tag. 
  • The tag will work appropriately only if placed in the <head> section or an HTTP header. 
  • Tag indexable pages.
  • Include the primary page version in your XML sitemap. 


A canonical tag can greatly benefit your SEO, but it is not the answer to everything. There are some limitations to keep in mind:

  • Only a fraction of link authority is consolidated. If page X tags page Y as its canonical version, X will most likely be excluded from the index. But only part of link authority will be shifted from X to Y. Webmasters cannot measure the value transferred from one page to another, since search engines provide no precise details. They neither confirm nor refute the speculations that all value can be passed on from one virtual location to another, keeping the community in the dark. Remember that the key purpose of a canonical tag is to prevent the indexing of duplicates. 
  • A canonical tag does not solve crawling issues. To understand that your pages should not be indexed, search robots still need to visit and crawl them. Chances are they will stop crawling your duplicate pages or do so less frequently, but there are no guarantees. Do not expect canonicalization to manage your crawl budget. Work on your Robots.txt file instead. 

Remember that canonicalization is only one of many optimization techniques for improving your brand’s online exposure. If you need competent SEO advice, contact the Clever team, and let us assemble a unique toolkit for your project.