What is a canonical tag?
The canonical tag has been supported by major search engines as early as 2009, but despite the benefits it offers, it has often not been implemented due to lack of knowledge about this technique and its purposes.
The Rel=Canonical tag is part of the HTML header on a web page, right here we place other elements such as the title tag, Meta Description tags and keywords. For example, if we have:
Each of these URLs refers to the same content on the home page of our website: these URLs make no difference to a user, but nevertheless since the search engine does not know which page should be the source of truth, it may happen that it algorithmically chooses a canonical URL for you and does not index the ones you wanted to rank.
In other words, if we have a web page that can be accessed through multiple URLs or pages that have almost the same content, we must specify which of these is the one with authority by setting our canonical.
Setting a canonical URL, then, is a similar process to a 301 redirect, only instead of actually redirecting to another page it redirects all variations to the URL we have chosen as authority (canonical URL).
How is our content duplicated and whyare they duplicated and whyshould we canonicalize?
There are many factors that can generate duplicate content, particularly if we use system-generated URLs. Let’s look at some common examples of duplication:
- E-commerce sites where filters for price, color, availability, etc. can be applied which generate new URLs.
- URL for the mobile version of our website.
- Country URL, i.e. when using several country-specific URLs (without changing language), the content remains largely the same, showing only some minor differences.
- Session ID URLs automatically generated by the system.
- URLs of print-optimized versions of the same content.
So why canonicalize?
As mentioned above, the use of canonicalization helps us to control these duplicate contents, it also allows us to protect our unique contents by avoiding diluting their ranking ability canceling all our SEO efforts.
Canonicalization also benefits large-scale companies with complex web development cycles. They can take advantage of the canonical tag, being an easily implementable solution, instead of applying more complicated and costly measures.
Finally, this method allows us to improve the user experience without interrupting the navigation of our visitors by moving them from one URL to another and saves us time and work by avoiding writing long redirect lists for each URL concerned.
How to apply the canonical tag
Let’s explain how to use this tool by helping us with Google’s guidelines on duplicate content and solutions through canonicalization:
Marking a URL as canonical and grouping duplicates
Suppose we have chosen the URL https://contenido.com/cars/cars-black as our canonical despite several other URLs leading to the same content.
To mark this URL as canonical we must mark all duplicate pages with a link element rel=”canonical” by adding a <link> with attribute rel=”canonical” to the <head> section of the duplicate pages. This element should point to our canonical page, for example: