If you have to publish different versions of very similar pages (for instance products in different colours) canonicals can solve the duplication indexation issues. Search engines do not like duplicate content, as they do not add any value for the user. Canonicals enable you to refer to the master URL so that only one version gets indexed.
The canonical tag appears in the head area of the HTML code. If a canonical URL is correctly marked, only the original source is used for indexing the search engines. The canonical property can also be set via the server.
<link rel="canonical" href="https:/www.mysite.com/url" />
Example of Cases when Canonicals should be used
- Online shops with products that can be sorted differently (for instance by colour or price) creating a new URL each time.
- Many working URLs for the start page (for example “/”, “/index.html” or “/home.html”) and redirects are not an option.
- URLs can be called in different formats. For instance with / variations, or upper/lower case, etc.
- Content is accessible in different formats or versions
Potential Errors (we often observe)
- Canonical points to a 404
- Canonical uses relative path instead of the full URL
- Canonicals are combined with “nofollow” or “noindex, this would send mixed signals.
- Canonicals incorrectly matching hreflang.