What a canonical tag is and how it fights duplicates

In short

A canonical tag is how you tell Google "this is the main version of this page." You need it when the same content is reachable at several addresses, so the search engine does not treat them as duplicates and split your rankings.

Where duplicates come from

One page often opens at several addresses: with and without www, with parameters like ?utm or without, with or without a trailing slash. To a person it is one page; to Google it is several identical ones. It does not know which to show and may rank all of them lower.

How canonical solves it

You add a canonical tag on every version pointing to the main address. Google understands the rest are copies and consolidates all the link weight and signals onto one page. Rankings stop splitting, and the right address shows up in search.

Common mistakes

The canonical points to a missing or blocked page
Every page's canonical points to the homepage instead of itself
www/non-www and http/https duplicates are not merged into one version

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FAQ

How is canonical different from a redirect?

A redirect physically sends a person to another address. A canonical keeps the page reachable but tells the search engine which one to treat as primary. It is the gentler tool.

How do I find duplicate problems?

The free SEO Nerve audit checks canonicals and warns you if a page is reachable at several addresses with no main one set.

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