Canonical tag

The canonical tag tells Google which of several similar URLs counts as the original version. It matters whenever the same page can be reached via different URLs, which happens more often than you might think.

Where duplicate content comes from

A page is typically reachable via http and https. With and without www. With and without a trailing slash. With and without index.html at the end. Plus additional parameters such as UTM tracking. One page quickly turns into four or five variants of the same URL. Without a canonical, Google does not recognise them as one page and splits the link equity between them.

What the canonical tag looks like

A link element with rel canonical in the head of the page. The href points to the canonical version. Important: use an absolute URL with https and the domain, not a relative one. Exactly one canonical per page, never several. A self-canonical, meaning a reference to the page's own URL, is allowed and even recommended, because it explicitly confirms to Google: this is the right address.

Common use cases

In e-commerce, when a product can be reached via several category paths. In A/B tests, when two variants of the same page exist. With a mobile subdomain, when both versions should be indexed but the desktop version counts as the main one. On AMP pages, as a reference to the standard version.

Anti-patterns

A canonical pointing to a page that does not match the source page, such as a product page pointing to its category. This confuses Google and often means the source page is no longer indexed at all. Canonical chains, where page A points to B and B points to C, instead of directly to C. Inconsistency between the canonical and the actual URL, for example the canonical points to https but the page still runs on http.

Related terms

Title tag · Sitemap · robots.txt