What is Canonical URL?
The definitive URL for a page, declared via <link rel='canonical'>, telling search engines which version to index when duplicates exist.
A canonical URL tells search engines 'this is the official version of this page.' If the same content is reachable at /blog/post and /blog/category/guides/post, the canonical tag on both should point to the primary URL. Without canonicals, search engines may split ranking signals across duplicate URLs, or index the wrong version. In Next.js, set canonicals via alternates.canonical in generateMetadata.