A canonical tag, <link rel="canonical" href="...">, tells search engines which URL is the main version of a page when the same or very similar content is available at several addresses. It consolidates ranking signals into one URL and keeps duplicates out of search results.
Why duplicates happen
- URL parameters for tracking, sorting or filtering, such as
?utm_source=or?sort=price. - HTTP and HTTPS, or www and non-www versions of the same page.
- Trailing slash and non-trailing slash versions.
- The same product in several categories of an online store.
- Content syndicated or republished on other websites.
How to use canonical tags
- Self-referencing canonical: every indexable page should point to its own clean URL. It protects you from parameter duplicates you did not foresee.
- Point duplicates to the main version: a filtered category page can point to the unfiltered category.
- Use absolute URLs, including https and the domain.
- Cross-domain canonical: when you republish an article on another site, the copy can point to the original.
A hint, not a command
Google treats the canonical tag as a strong signal, not an order. It also looks at redirects, internal links, sitemaps and HTTPS. If your signals contradict each other, for example internal links point to one version and the canonical to another, Google may choose a different canonical. The URL Inspection tool in Search Console shows which one Google selected.
Common mistakes
- Canonicals pointing to URLs that redirect, return a 404 or are noindex.
- Several canonical tags on the same page with different URLs.
- Pointing every page of a paginated series to page one, which hides the content of the other pages.
- Using canonical and noindex on the same page, which sends contradictory signals.
- Canonical tags added by JavaScript only, which Google may process later or not at all.
Check the canonical, noindex and other indexing signals of any page with our SEO Audit Tool.
Frequently asked questions
Canonical or 301 redirect?
Use a 301 when users do not need the duplicate URL at all. Use a canonical when the duplicate must stay available, such as a filtered view or a tracking URL.
Does a canonical tag pass link value?
Yes. Google consolidates signals from the duplicates into the canonical URL, much like a redirect.
Can I set a canonical in HTTP headers?
Yes. A Link header with rel=”canonical” works for files without HTML, such as PDFs.