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What is a Canonical Tag?

What is a Canonical tag?

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You have optimized your website or your webshop according to all the rules of search engine optimization and still, your web pages do not rank or the wrong page rank for a certain keyword?

Then you should have a look at your canonical Tags.

You don't know what a Canonical tag is or how to use it correctly?

Then you should read on.

In this article, you will learn what a Canonical tag is, why you should assign the Canonical attribute, how to use it and which mistakes you should avoid.


What is a Canonical tag?

canonical tag

A Canonical tag is a line in code that tells the crawling software of search engines (e.g. Googlebot) which URL should be included as the main URL in the index if there is duplicate content (identical or almost identical content) on a web page. This means that only the original document is included in the link database of the search engines (indexed) and displayed in the search results during the search.


Why does Canonical Tag exist?

Google and the other search engine providers want their users to be satisfied with the search results, i.e. to have a good user experience. However, if the search results show a lot of similar results that offer the user little choice, the user experience will suffer.

And now let's be honest.

Google and most search engines want to generate advertising revenue on the search results pages by displaying ads (e.g. Google Adwords ads / Google Ads) - in short: earn money. Who can blame them?

To ensure that people continue to use their search engine, they use every means at their disposal to ensure that users have the greatest possible benefit. With double or very similar results in the search results, this is not the case. This is why pages with such content are not ranked prominently, i.e. right at the top of the search results.

And to avoid this, you have the option of combining your duplicate content under one main page using Canonical Tag.


Unavoidable duplicate content without malicious intent

Sometimes there are several times the same content on a web page (Duplicate Content). This can also be done without malicious intent. If, for example, there is a print version of a website, or if, depending on the device or filter options, duplicate URLs with the same content occur, these should be combined under a canonical link. If external content is used, it must of course also be marked as a source in the Canonical tag.

Another example of unavoidable multiple identical contents is the products of an online shop, which are offered in different colors, sizes or variants. If each of these variants has its own page with its own URL, it must be tagged with a Canonical tag that points to the main product page.

Here is an example.


What does the Canonical Tag communicate?

A Canonical tag is used to determine which URL should be the source for the multiple contents of a web page.

This is done by adding the URL of the source as a Canonical tag or Canonical attribute in the document.

This tells the crawler to be careful not to include this page here for this content, but to include the URL from the Canonical tag in your index instead. The principle is the same as for a permanent 301 redirect.


How do I set the Canonical tag?

The Canonical tag is inserted into the Head area. It is specified that a link is to be established to the following URL and that this link target is to be understood as the source for this document.

Let's look at the example of a shop page with different variants of a product.

  • Product page (refers to itself in the Canonical tag) URL of this page: https://examplepage.com/produkt.html Canonical Link: <link rel=canonical" href="https://examplepage.com/product.html">
  • Product Variant 1 (refers in the Canonical tag to the product page)
    URL of this page: https://examplepage.com/product-variant-1.html
    Canonical Link: <link rel=canonical“ href=“https://examplepage.com/product.html“>

  • Product Variant 2 (refers in the Canonical tag to the product page)
    URL of this page: https://examplepage.com/product-variant-2.html
    Canonical Link: <link rel=canonical“ href=“https://examplepage.com/product.html“>

  • Product Variant 3 (refers in the Canonical tag to the product page)
    URL of this page: https:/examplepage.com/product-variant-3.html
    Canonical Link: <link rel=canonical“ href=“https://examplepage.com/product.html“>


It would look like this graphically:

canonical tag beispiel

Thus, a primary URL is given. Otherwise, arbitrary indexing would be carried out by the search engines.


The Canonical Tag in Search Engine Optimization

A clean and correct entry of the Canonical tag ensures that the crawling software indexes the pages correctly. The search engine optimization makes sure that Canonical tags are set correctly.


The influence of duplicate content on the ranking

Because Google removes pages from the index that deliberately contain external duplicate content, it's important to avoid it.

However, this is not the case for internal duplicate content that is not deceptive. However, multiple contents on a domain can have an impact on search results and ranking.


Because, on the one hand, the crawler cannot see which content of a domain is best displayed in the search results and, on the other hand, several pages share the ranking.


Caution - Mistakes and incorrect handling of the Canonical Tag

Even when setting a simple tag, errors can occur, which can even lead to the web page not appearing in the index.

Therefore, there are some points to keep in mind:

  • Canonical tags only make sense if the content is indeed identical or almost identical.
  • The Canonical tag is best set as a complete, i.e. absolute URL, since a relative path specification is not always interpreted correctly by the crawler.
  • Google prefers https, therefore the http document should refer to the https, so that this is included as canonical URL.
  • Numbered pages are not identical contents, but parts of a content, which are connected by rel="next" or rel=prev". Here a Canonical tag, which refers to the first page, would be set wrong.
  • Multiple Canonical tags may not be used in a document, as these are not processed by the crawlers.
  • Canonical Tags and hreflang attribute: If a web page is marked with hreflang attribute, the Canonical tag should refer to itself. Otherwise, Google receives contradictory signals. The hreflang tag would indicate that another language version is available, the Canonical tag would make this version the original URL.
  • If the Canonical tags within a domain refer to the home page, only the home page may be indexed. This should be kept in mind.
  • The target page of the Canonical tag should not refer to other Canonicals. In this case, you should identify their target page in the Canonical tag instead.
  • If "noindex", "disallow" or "nofollow" is set at the same time, the crawlers cannot follow the Canonical URL and add it to the index.
  • The Canonical tag must neither be set in <body> nor in the meta tags but must be in the <head> area.
  • The Canonical URL must be accessible, therefore 404 errors on excellent websites must be avoided.



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