Canonical tag

What is the Canonical Tag?

The Canonical Tag is an HTML element that is inserted in the of the source code as a Rel attribute. It is used to tell the crawlers that here is a text with identical content, and that this URL is the canonical URL. The same applies to a text with similar content.

When is the Canonical Tag used?

In SEO OnPage optimization, this tag is used especially in case of difficulties with duplicate content. It informs search engine bots that the page with the canonical tag is the original source. 

Duplicate content can occur for various other reasons:


  • The website is accessible with and without www
  • The website is accessible with upper and lower case letters 
  • The website can be reached with http:// or https://.

Other uses of the Canonical tag

  • hreflang link attribute is used to indicate that several linguistic variants exist for the content and that the content with this URL is assigned to a country. With this tag one refers then to oneself. 
  • Avoid duplicate content at different URL's with the same content.

Online stores and the Canonical Tag

In online stores, where a product is subject to several categorizations or sorting parameters, duplicate content can occur very quickly. Example: swim shorts of a certain company can be found under brand, size, color, etc.. Here it can quickly come to different URLs for a product. 

In order to avoid an arbitrary indexing or a possible penalty, it is recommended to use a Canonical tag on the main product page.

What are the advantages of the Canonical tag?

A significant advantage of the Canonical tag is that it is relatively easy to include it in the source code of the page in question.

How is the Canonical tag included in the source code?

The Canonical tag is inserted in the source code in the HEAD area as hyperlink and still receives the attribute rel to it. The exact HTML code snippet is :

<link rel=”canonical” href=””>

What mistakes can you make when using this tag?

  • One of the most common mistakes is that the target page you are linking to does not exist.
  • In pagination, when the rel next and rel prev attributes are used, a canonical tag is set on the first paginated page.
  • target page also points to another page with a canonical tag, creating a canonical chain.
  • The canonical page has the attributes noindex, nofollow and disallow.
  • The reference to a page irrelevant to the topic.
  • One points to a page that is redirected with a 301.

What should be considered when using the Canonical tag?

The first thing to check is whether there is actually duplicate content.

More tips:

  • You can use only one canonical tag per web page. Otherwise, the crawlers may ignore it.
  • Redirected pages should also be reachable and not have a 404 error page.
  • The referred page should not have a "noindex", "nofollow" or a "disallow".
  • When specifying the path, you should always specify absolute paths and not relative ones. Examples of an absolute path:; relative path:
  • Always specify the canonical page (not without www)
  • One should also note the trailing slash. If the canonicalized page has a slash, then you should indicate that as well.

If you have problems with duplicated content, contact us! As SEO Agency in Munich we are sure to find a solution.

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