What is a canonical link? (canonical URL)
The canonical link is a technical indication placed in the HTML code or in the HTTP header which specifies the canonical version of content. It is generally implemented in the following form:
In other words, if several similar or identical pages exist, the rel="canonical" tag is used to indicate to search engines which URL should be considered as the main version to index and position.
The definition of the canonical link is directly linked to the management of duplicate content, the consolidation of SEO signals and the good organization of the architecture of a site. It is a fundamental element of technical SEO.
Why use a canonical URL on a website?
In practice, it is very common for the same content to be accessible via several different URLs. This may be due to URL parameters, filters, page versions, tracking parameters or even technical variations.
Without a canonical link, these different versions can be interpreted by Google as separate pages. This can lead to several SEO problems:
- presence of duplicate content in the search engine index;
- dispersion of PageRank between several similar pages;
- difficulty for Google to identify the main page;
- waste of crawl budget.
By declaring a canonical URL, you clearly indicate to engines which version should be favored in search results.
How does the rel="canonical" tag work?
The rel="canonical" tag acts as a signal sent to search engines to tell them which page should be considered the official version of content.
Some important points to remember:
- the canonical is a strong signal but it remains an indication that Google can choose to follow or not;
- it is recommended to use absolute URLs in the href attribute;
- most pages should have a self-referencing canonical pointing to their own URL;
- the tag can be placed in the HTML code or in the HTTP header.
To be effective, the canonical tag must remain consistent with all of the site's SEO signals such as redirects, internal links or sitemaps.
Canonical link use case
The canonical tag is particularly useful in several common situations.
URL parameters and filters
URL parameters can generate multiple versions of the same page.
- /category/shoes/
- /category/shoes/?color=black
- /category/shoes/?utm_source=newsletter
In this case, we indicate a main canonical URL, often the version without parameters, in order to avoid indexing all the variants.
E-commerce and product sheets
On an e-commerce site, a product can sometimes be accessible via several categories or paths. The canonical link then allows you to define a single reference URL for the product sheet.
Alternative versions of content
Some pages have a printable, PDF or mobile version. The canonical allows you to specify which version should be considered the main version.
Management of technical variants of a site
Canonical can also support the management of HTTP or HTTPS versions as well as variants with or without www when there are several possible URLs for the same page.
Best practices and common mistakes
Use only one canonical tag per page
Each page must declare a single rel="canonical" tag. Multiple canonicals can be confusing for search engines.
Use a self-referencing canonical
In the majority of cases, a page must point to itself as the canonical URL in order to avoid any ambiguity for the engines.
Use clean URLs
The canonical tag must point to a valid and accessible URL. It must not redirect or lead to a non-existent page.
Stay consistent with other SEO signals
The canonical must remain consistent with redirects, internal links and other technical tags like hreflang or noindex.
Canonical link and technical SEO
The canonical link is one of the fundamental elements of a technical SEO audit. It helps clarify the structure of the site and helps search engines identify the main version of each page.
To check a canonical, several methods exist:
- inspect the source code of the page;
- use browser development tools;
- analyze the site with an SEO crawler;
- use the URL inspection tool in Google Search Console.
Correct configuration of canonicals contributes to cleaner indexing and better consolidation of SEO signals.
FAQ: Frequently asked questions about the canonical link
What is a canonical link in SEO?
A canonical link is an HTML tag that tells search engines which URL should be considered the primary version of content when there are multiple similar pages.
Does canonical linking remove duplicate content?
No. The canonical does not remove duplicate pages but simply tells the engines which version should be favored in the index.
What is the difference between canonical link and 301 redirect?
A 301 redirect permanently transfers the user and search engine to another URL. The canonical link leaves the different pages accessible but indicates which one should be considered the main one.
Should we use a canonical on all pages?
It is recommended to use a self-referencing canonical on the majority of pages to clearly indicate their main URL to search engines.
How to check the canonical link of a page?
Simply open the source code of the page and search for the rel="canonical" tag or use SEO tools or Google Search Console to identify the canonical URL recognized by Google.
What happens if the canonical link is misconfigured?
An incorrect canonical can send bad signals to search engines and lead to the wrong page being indexed or an important page losing visibility.
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