Canonical tags

The use of canonical tags avoids duplicate content. Canonicals play a crucial role in search engine optimization (SEO). For this reason, the term SEO Canonical Tag is often used synonymously. In order to fulfill its task, the tag refers to the original resource for pages with identical content. For this purpose, the corresponding reference is inserted as markup in the source code of the web page whose content is to be ignored by the search engines.

The source resource is referred to as the canonical URL. In this context, a canon is a collection of related web pages with different hierarchies. The pages of the canon that are lower in the hierarchy refer to the URL at the top of the hierarchy by means of the canonical tags ("canonical tags" = the code parts addressed).

For example, in the application, an SEO Canonical Tag looks like this:

Output pages of the same content:

‍

• http://www.musterbeispiel.com/beispiel.html (kanonische URL)
• http://www.musterbeispiel.com/beispiel_print.html (Druckansicht, aber potenzieller Duplicate Content)

‍

Tag for the page with a potential duplicate content:

Use case examples:

Pages can be called up with or without "www

‍

• Print views
• Pages are accessible via "http" and "https
• Pages can be called with or without trailing slashes ("/")
• Start pages can be accessed via different URLs
• Content also runs on other pages (for example, as a ticker)
• Server works with rewriting of the URL, which allows variations in spelling
• Web page variants for mobile devices are called with "m." in front of the URL

SEO Canonical Tag: Importance for Search Engine Optimization 

The above list of examples of use cases for Canonical Tags shows that duplicate content can happen quickly and unknowingly. However, Google and Co. penalize duplicate content. The background to this is that it is considered a deceptive attempt to place relevant keywords on a platform as often as possible without much effort, for example. In the case of duplicate content on external pages, the search engines also suspect unauthorized copies and therefore penalize the Internet platform concerned.

However, Google and co. also know that es has legitimate cases for duplicate content - for example, as a print view or a special playout for smartphones and tablets. The Canonical tags are therefore accepted as a simple solution to delete permissible duplicate content for consideration. It is therefore recommended es that each page is equipped with a corresponding tag that first refers to itself. This can be easily changed if necessary: For example, if one notices when creating the page that es is a print view, which is why a different reference must be included, this can be implemented directly.