Tags play an important role in search engine optimization, as they can be used to communicate with a crawler, for example. This lexicon entry shows the advantages of this and the possibilities that arise.
What is a canonical tag?
The canonical tag is used to identify a website with duplicate content, otherwise it will be penalized by Google after detection. A page with repetitive content will always be lower in the ranking or cannot be found at all, which is why a canonical tag (attribute: rel=”canonical”) is set.
When must the canonical tag be used?
Online stores in particular have a problem with duplicate content, as this occurs with every product variant (such as size and color). The same happens with blogs if they want to display the same content more than once, such as an article that has been used once under its main category and once as a “supplementary range” for another article. With ordinary websites, it is often the print versions that inevitably lead to duplicate content.
There is also technical duplicate content if a website can be accessed both via “www.” and without “www.”. The situation is similar with independent mobile versions. These are all reasons for using a canonical tag. It is even strongly recommended to use it.
How is the canonical tag entered?
There are two specific options for using canonical tags. Firstly, the source code can be used, which is integrated into the header. However, only one URL can be read; if there are several canonical tags in the source code, this will be ignored by the search engine and indexing will still take place. It is also important to ensure that there are no other attributes such as “noindex” or “disallow”. The “nofollow” attribute should always be omitted from your own pages.
The second option is based on the server, as this can automatically add a “canonical tag” to the original page on the shopping cart page, for example. This is also useful whenever an online store is operated.
What should I bear in mind when using the canonical tag?
Before using a canonical tag, it is important to check whether it is actually duplicate content. It is always duplicate content if the majority is identical. Furthermore, the referring page must also be accessible and must not refer to a 404 page, otherwise this will also have a negative effect. The following rules must also be observed:
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Only one canonical tag per subpage.
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Always link with absolute URLs (with https://).
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The linking page with canonical tag must not contain any other attribute.
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Paginated pages with attributes rel=”next” and rel=”prev” should not be marked, as this is not duplicate content in principle.
