SEO Glossary: Canonical Tag

What is a canonical tag?

The canonical tag is now one of the most important tools and a must-have for onpage optimization. It helps to avoid errors and the associated penalties from search engines such as Google.

 

It often happens that websites and subpages contain duplicate content. In this case, we are talking about duplicate content. If no canonical tag is recognized, all pages containing the duplicate, repetitive content are penalized. These then rank lower in the search results.

 

To avoid such problems, the canonical tag (rel="canonical") is set in the header area. It is placed on all pages that contain the duplicate content and also links to the original website.

 

If a search engine bot visits a subpage and sees the canonical tag, it simultaneously recognizes the original, linked page and ignores the page with the duplicate content. At the same time, the PageRank is transferred to the original page.

 

 

When is a canonical tag useful?

 

Some examples of when the canonical tag makes sense:

 

• If products in an online store are sorted by price or color, for example, duplicate content is created
• If a blogger publishes a post and tags it in several categories, duplicate content is created. If the canonical tag is missing, the content can be considered duplicate.

 

How is a canonical tag used?

 

There are two ways to incorporate the canonical tag. These are explained in more detail below:

 

 

1. code in the HTTP header

 

In the source code of a page with duplicate content, a code is placed in the HTTP header. In addition to the canonical tag, this also contains the target URL to the original content.

 

Example:

 

<link rel=”canonical” href=”http://www.domain.de/originale-url”/>

 

It is important to note that only one canonical tag may be placed on a page. If several canonical tags are included, they will be ignored by search engine bots and the duplicate page will be fully indexed.

 

In addition, it is important that there are no meta tags such as "disallow", "noindex" or "nofollow" are allowed. Otherwise, the function of the canonical tag will be disrupted and complications will arise.

 

2. transfer of the canonical property

 

The second option is to transmit the canonical property directly via the server. A classic example here is an online store. If the customer places several products in the shopping cart, these are transferred including the canonical property. If bots visit the subpage, indexing is therefore excluded.

 

The same applies to websites where users can filter different categories and products with an ID. If, for example, another product variant is selected (e.g. a different color), the canonical tag is added directly to it. In this way, duplicate content is avoided.