A canonical URL is the version of a page you tell search engines to treat as the "real" one.
When the same content sits on several URLs, a canonical tag points to the preferred one. This is a signal, not a directive: Google can select a different canonical.
Put simply: Telling Google "this is the original, index this one."
Why it matters
- Avoids duplicates. Stops near-identical pages competing with each other.
- Consolidates signals. Links and authority point to one URL, not many.
- States a preference. Helps Google choose among duplicate URLs; the declared URL is not guaranteed to be selected.
When you need it
- Filtered URLs. Sorted or filtered product pages with the same items.
- Protocol variants. http vs https, www vs non-www versions.
- Reposted content. Syndicated articles that live in more than one place.
Frequently asked questions
When do I need a canonical tag?
Whenever the same or very similar content sits on more than one URL, such as filtered pages, tracking parameters, or http and https versions.
Is a canonical tag a redirect?
No. A redirect sends users to another URL; a canonical leaves the page accessible but tells Google which version to index and credit.
What happens if I get canonicals wrong?
You can hide the wrong version from search or split ranking signals across duplicates. Point each canonical at the single URL you want to rank.
Further reading: Google canonical guidance.