Canonical Tag

A canonical tag is a link element in the head of a page:

<link rel="canonical" href="https://example.com/shoes/">

It tells search engines which URL should represent a group of duplicate or near-duplicate pages, such as /shoes/, /shoes/?sort=price, and the www and non-www versions. Use absolute URLs, and place only one canonical per page. For files without a head, like PDFs, you can send the same signal through a Link HTTP header.

The key point is that a canonical tag is a hint, not a directive. Google weighs it alongside other signals and can choose a different URL. In rough order of strength, a 301 redirect is the strongest signal, a rel canonical tag is strong, and listing the URL in a sitemap is weak. When Google overrides your choice, Search Console’s URL Inspection tool shows both the user-declared canonical and the Google-selected canonical.

A self-referencing canonical, where a page points to itself, is good practice because it guards against parameter and tracking variants. Canonicals can also point across domains, for example when an article is syndicated. Don’t use robots.txt or noindex to consolidate duplicates. Blocking the duplicates stops Google from seeing them as duplicates of your canonical at all.