Technical SEO
What is a canonical tag.
In short
A hint telling Google which URL is the main one when the same or very similar content is available at several addresses. It is set with a link rel="canonical" tag in the page code.
Also known as: rel=canonical, canonical URL
Why canonicals exist
The same content is often available at several URLs: with a sort parameter, a campaign code, with and without a trailing slash. To Google these are separate URLs. The canonical tag says which one is the main version that should appear in results, and treats the rest as copies.
What it looks like
You add <link rel="canonical" href="https://example.com/running-shoes/"> in the head of the page. Ideally every page has a canonical, including self-referencing ones, with the full https URL.
A canonical is a hint
Google treats the canonical as a strong suggestion, not a command. If other signals contradict it, for example internal links point to another version or the sitemap lists a different URL, Google may choose a different one. Search Console shows which URL it picked.
Common mistakes
- All paginated pages point their canonical to page one, so products on later pages get indexed less well.
- A canonical pointing to a page that redirects or returns an error.
- Canonical and noindex on the same page, which sends conflicting signals.
- A canonical injected by JavaScript that differs from the one in the HTML.
- Pointing the canonical to entirely different content, such as every product to its category.