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Canonical tags explained

Published 2 November 2026

In short: a canonical tag tells search engines which URL to index when the same content is reachable at several addresses. Put a self-referencing canonical on every indexable page and make redirects, internal links and your sitemap agree with it.

Why duplicates happen

Few site owners create duplicate content on purpose, but a single product can easily be reachable as /shoes/red-runner, /red-runner?color=red, /red-runner?utm_source=newsletter and the same paths on www and http. Search engines then have to guess which one to show, and links and other signals get split between them. A canonical tag removes the guesswork.

How to write one

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

Put it in the <head>, once.
Use the full absolute URL, with your preferred protocol and host.
Point it at a page that returns 200, isn't redirected and isn't noindexed.
Render it in the server HTML; a canonical added by JavaScript may be read late or not at all.

Typical cases

Tracking and sort parameters: canonicalise to the clean URL. Paginated lists: page 2 should canonicalise to itself, not to page 1, because it lists different items. Product variants: canonicalise to the main product unless each variant has distinct content worth ranking. Syndicated articles: ask the republisher to add a cross-domain canonical to your original. http and www: fix with 301 redirects first; the canonical is the backup.

Signals that override your tag

Google treats rel=canonical as a hint. It may choose a different URL if your internal links point elsewhere, your sitemap lists another variant, the canonical target redirects, or the two pages aren't really the same. Search Console's URL Inspection shows both the "user-declared" and the "Google-selected" canonical; if they differ, look for one of those conflicts.

Check it

Our canonical checker shows the declared canonical, redirects and the common conflicts for any URL in a few seconds.

Frequently asked questions

Canonical or 301 redirect?

Use a 301 when the old URL should stop existing for visitors. Use a canonical when both URLs must keep working, such as filtered or tracked URLs.

Does a canonical pass link value?

Google generally consolidates signals to the canonical URL it selects, similar to a redirect, as long as the pages are true duplicates.