What it is and how it works

Do you know the meaning of canonical in SEO? It’s an HTML element inserted into the code of web pages to avoid issues related to duplicate content. The canonical tag is used to indicate to Google which URL is the most relevant, preventing the algorithm from choosing it automatically.

While it’s now known how to increase the visibility of online resources in the eyes of Google, you also need to know what can hinder the positioning of specific content. The algorithm seeks maximum clarity when it scans websites. If it finds that the content of two or more pages is the same, it interprets them as duplicates, penalizing their position in SERPs.

Properly applying the canonical tag is fundamental for those who optimize websites, to recognize duplicate content and guide indexing. So, a course to become an SEO Specialist is increasingly important today to create a winning content strategy.

On this page, I will try to clarify:

  • the meaning of canonical in SEO
  • how the canonical tag works
  • issues related to URLs and duplicate content
  • differences between the canonical tag and 301 redirects
  • best practices in using the canonical URL.

Canonical in SEO: what it is and what it is used for

When we talk about canonical SEO, we are referring to a specific attribute that is inserted into the HTML code to indicate a property. In essence, it is used to indicate to the search engine which version of a URL is the most representative of a set of duplicate content. By adding the rel=canonical attribute, you indicate what the canonical URL is, identifying the preferred version of a web page and facilitating its indexing.

The use of canonical tags in SEO is not a mandatory practice for SEO managers, but it is recommended by Google because it makes it clearer to the software responsible for analyzing web content (the crawler) which URL you want to indicate as the original content. Canonical pages will be scanned frequently, while duplicates will be viewed less frequently, reducing the analysis load on the site.

This process is called canonicalization, which is the selection, through the use of the canonical tag SEO, of content considered original for a site, performed to resolve any issues of duplicate content on different URLs.

Derived from Latin, from the term “canon”, which means a rule or criterion to be adopted, canonical means conforming to this principle. Canonicalization of URLs allows you to establish a reference URL (“canonical”).

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Why is the rel canonical tag important?

The canonical in SEO serves a simple purpose: in the case of duplicate content, it instructs Google’s algorithm on what should be considered the definitive content. The use of duplicates is seen as deceptive by Google, resulting in a negative user experience as the same content may appear repeatedly in search results. Consequently, these duplicates affect the rankings of the websites containing them.

This becomes evident when working on search engine optimization; it’s common to find the same pages but with different URLs within the same website. These URL variations often occur naturally during website construction and can be generated automatically by the Content Management System (CMS), which means we may not be aware of a specific web resource being duplicated and associated with a different URL.

The most common example of duplicate content is related to the homepage:


All these URLs lead to the same resource, which is the site’s homepage. This confuses the search engine because it doesn’t know which one to index. This also occurs when many tag or category pages have the same content as others, which is common in the world of blogs.

The canonical SEO simplifies the site’s scanning for Google’s algorithm, suggesting which pages should be given priority for indexing and ranking.

Among the tools for webmasters provided by Google, some tools suggest canonical URLs for your site, and you can verify if the indications have been inserted correctly. For instance, if you are concerned that you haven’t selected the best canonical URL among your content, you can check the address using the URL Inspection tool in Search Console, which will display the canonicalization chosen by Google.

Duplicate pages and URLs: what issues do they cause?

Now that you understand what Canonical SEO is for and why it’s important, let’s discuss the problems caused by duplicate content.

canonical urls duplicates

Duplicates hurt organic rankings because Google can’t determine which page provides the most relevant content for a query. Most instances of automatically detected duplicate content by Google are caused by improper use of URL parameters or poor content organization or management.

This often occurs in the case of e-commerce websites that sell the same products and use descriptions from suppliers, resulting in the same textual content appearing on multiple e-commerce sites.

Even URL parameters in URLs, such as those related to click tracking and Google Analytics codes or other web analytics software, can lead to the creation of entirely duplicated content. The same issue arises for sites that make content available in both HTTP and HTTPS versions. If both versions of a page appear on the search engine results page (SERP), content duplication becomes a problem.

Duplicate content, when detected by scanning bots (Googlebot), can be penalized by Google in various ways:

  • by applying a filter to the content so it doesn’t appear in the SERP;
  • through the Google Panda algorithm, which directly penalizes pages involved in systematic copying;
  • by imposing sanctions (this occurs in the case of plagiarism complaints).

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How to insert canonical URLs for SEO

As you’ve understood, the use of canonical in SEO can resolve issues related to duplicate content that isn’t suitable for search engines because Google can’t determine which text is the original, best, or most relevant for the query.

When Google’s bot indexes a site, it attempts to identify the main content of each page. If it finds multiple resources on the same domain that seem similar, it selects the page it deems most complete and functional, marking it as canonical.

We can insert canonical URLs for SEO either through a content management system like WordPress or manually. Using these canonical links is straightforward; you only need to include a small line in the header section, and you’re good to go. If you want to modify it directly in the HTML, follow this example:

  • URL:
  • Canonical URL: <link rel=”canonical” href=”” />

The linked URL tells the search engine that the product page is the “original” address, and the URL with the “session ID” is a copy. For precautionary reasons, it’s advisable to assign a canonical tag to every URL. If there is no copy, link any URL to itself.

Use the rel=canonical Attribute

To designate the canonical page, you can set the rel=canonical. To do this, simply insert the canonical URL, intended as the main one, in the HTML tag. This way, we are telling Google which page to index. It’s advisable to use absolute URLs and not relative ones with the link rel=”canonical” element.

Using this attribute correctly helps improve site performance. The HTML element should be placed in the <head> section of both the canonical and duplicate pages, like this:

  • <link rel=”canonical” href=”http://mysite/original-page” />

Through WordPress, you can install a plugin like SEO by Yoast that allows you to specify the canonical link for each resource without touching the code. The best scenario to use the canonical URL in this way is when you have pages with very similar content for some reason. Additionally, HTTP headers for canonical links are very useful when canonicalizing PDF files.

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Insert them into the sitemap

In defining each Canonical URL for SEO, you can make use of the Sitemap. This is a file containing all the web addresses of a site, listed in order of creation. The Sitemap has two main functions:

  • facilitating the user in finding content of interest on a site;
  • indicating to Google’s algorithm the organization of the website’s content to facilitate scanning by crawlers and achieve as adequate indexing as possible of the pages.

How to proceed? Identify the canonical pages, establish a canonical URL for each, and finally, insert them into a Sitemap. All resources classified in this way are then suggested as primary copies. Although Google does not guarantee the consideration of all Sitemap URLs as canonical, this method allows for a simple definition, which is advantageous, especially for large sites with a lot of content. Furthermore, Sitemaps are useful for signalling to Google the pages you consider most important on your site.

Pay attention to the following indications

In the correct implementation of Canonical in SEO, if one of the variants is an AMP resource, it is advisable to follow specific guidelines to signal to spiders the canonical page and the AMP variant.

When using the rel canonical tag, do not take the following actions:

  • use the robots.txt file for URL canonicalization;
  • use the tool to remove URLs in Google Search Console to canonicalize content, as it would remove all versions of a URL from search;
  • define different URLs as canonical for the same resource (e.g., one URL in a Sitemap and another URL for the same page using the rel=”canonical” link);
  • use noindex to prevent the selection of a canonical page. This indication is useful to exclude the resource from the index, not to manage its selection;
  • define a canonical page through hreflang tags. Specify a canonical URL in the same language or the best substitute if there is no suitable canonical page in the same language.

Canonical SEO vs 301 Redirect

301 redirect and canonical SEO are not the same. While a 301 redirect redirects the user to another website, the canonical tag highlights the relevance of a URL compared to its duplicate. Despite this clear difference, there are many similarities, so you can get confused. Besides being used similarly in similar situations, their similarity also lies in the fact that both 301 redirects and rel canonical transfer the page’s ranking.

rel canonical in seo

While a canonical tag is just a suggestion to Google, a redirect is a directive (it directs you to another resource); this is the substantial difference that explains when to prefer one over the other.
Simply put, if you have two identical or very similar pages and don’t need both to be active, you should use a 301 redirect.

If you have an e-commerce site with many products, you might have several pages with similar products (e.g., a grey shirt with a logo compared to a red shirt with a logo). If you want Google and other search engines to index only the dominant versions of these products but still want users to see and purchase both color variations, a canonical tag is an ideal choice.

Best practices in using canonical in SEO

Use canonical SEO following these guidelines:

  • when the content is extremely similar or exactly duplicated on two different URLs, two or more URLs, you should always consolidate and canonicalize them into one.
  • if a piece of content, product, or event is no longer available and there is a better match on another URL, consider the latter as canonical.
  • if another site offers the same content as yours, you can request the addition of the canonical tag to your resource; this way, canonicalization will prevent the positioning of the “copy.”
  • avoid mixed signals. You should try not to canonicalize “page A” to “B” and then “page B” to “A”. Signals need to be clear; otherwise, it can complicate Google’s scanning, making the indexing of your website more challenging.
  • be careful not to make “almost” duplicates canonical: you can use the canonical tag on very similar pages, but proceed with caution. There is much debate on this topic; typically, you are allowed to use canonical tags for very similar pages, such as a product page that only differs in currency, location, or some small product attribute. Keep in mind that non-canonical versions of that page may not be suitable for ranking, and if they are too different, search engines may ignore the tag.


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