When should canonical tags be used?

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By definition, canonical tags are not a factor that search engines necessarily take into account. Since the code must be implemented individually for each duplicate content and alternative URI, the question arises as to whether the associated relatively high management effort is worthwhile. Below are examples of situations where it is worth considering using this type of tag.

Content is spread across multiple dynamic URLs
Dynamic URLs play a very important role today, especially in the field of e-commerce. Custom pages are certainly an excellent and easy way to present the same content (with slight variations) to different users, but they also cause pharmaceuticals email database problems for search engine crawlers. Canonical tags are, in this sense, highly recommended to avoid the possible classification of duplicate content.

The same content can be accessed with different URLs
In terms of structure, some web projects, such as blogs, online shops or digital guides, offer content distributed simultaneously in different categories and often also on different URLs. Thus, a shop could redirect, for example, to the general page of the article “green shirt” under the following URLs:

mi-tienda.shop/moda/camisa-verde
mi-tienda.shop/modadeverano/camisa-verde
mi-tienda.shop/modadeinvierno/camisa-verde
The fact that content is available under different URLs is common when the structure of a website has been modified or an entire domain has been moved. In these cases, 301 redirects are a good option, but if this cannot be done technically, then the link element rel=“canonical” is a good alternative.

The same content is available on different domains
The canonical tag can also be used with external domains. The procedure is the same as for internal domains, meaning that an exact URL must also be provided as the main version. This way, you can offer your content on another domain without generating duplicate content. With this method, SEO-relevant factors are also passed on to the main URL, which can significantly improve its performance.

The contents have different formats
In some situations, it is important to publish content in different formats and not only offer, for example, a form in HTML version, but also as a PDF file and in a printable version . In this regard, it is recommended to use the canonical tag so that search engines do not have to evaluate each of the variants separately and end up classifying the wrong one.

Advice
If you have a valid SSL/TLS certificate, it is recommended to convert HTTPS URLs to canonical and redirect non-secure (HTTP) variants to them. The same applies to mobile or AMP pages, in which case canonical tags are even mandatory.

Canonical tag: common mistakes
A canonical URL is in many situations the best option to avoid duplicate content . The major search engines take the canonical element into account when indexing and recognize that the website has no intention of ranking in parallel with duplicate content. In addition, the positive signals from the search engines are gathered in the main URL, which improves the positioning chances. At this point, however, it should be stressed that the use of canonical tags can become a negative factor if they are not applied correctly. In the following paragraphs we show you the most common “canonical” errors .