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What is a canonical URL?

Last updated .

A canonical URL is the address that a search engine selects as the representative version of a page when the same or very similar content can be reached at several URLs, for example with and without www, with tracking parameters or over HTTP and HTTPS. The canonical link relation is defined in RFC 6596.

Definition
Canonical URL
The URL a search engine treats as the main version of a page that is reachable at several addresses, signalled by rel=canonical, redirects and sitemaps.

How it is signalled

Google describes redirects and rel="canonical" as strong signals and inclusion in a sitemap as a weak one, and none of them as a command: Google combines them and chooses. It recommends absolute URLs, a self-referencing canonical on the canonical page itself and advises against using robots.txt or noindex for canonicalization.

The costly mistake

A canonical that points to another host, such as the staging site or an old domain, after a migration. Search engines then treat the production page as a copy.

A worked example

A shop answers at http://example.com/shoes?utm_source=mail, at https://example.com/shoes and at https://www.example.com/shoes: one page, three addresses. Choose one, for example https://example.com/shoes. Redirect the HTTP and www variants to it with a 301, put <link rel="canonical" href="https://example.com/shoes"> in the page head (absolute, and the same as the page’s own address) and list only that URL in the sitemap. Tracking parameters then fold into the one address instead of becoming separate pages.

What to check

That each indexable page’s canonical is an absolute HTTPS URL on the production host equal to its own address, and that redirects, internal links and the sitemap name the same URL.

Sources

Read on . Standards and vendor pages change; confirm the current text before you rely on it.

Guides that use this term

  • RedirectA redirect is an HTTP response that sends a visitor or crawler to another URL. The permanent and temporary status codes and how Google treats each.
  • IndexingIndexing is how a search engine stores a page it has crawled so it can be returned for queries. What decides whether a page is indexed and why crawled does not mean indexed.
  • SitemapAn XML sitemap lists the URLs a site wants search engines to know about. Google’s size limits, how lastmod is used and what belongs in the file.

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