A canonical tag is an HTML element placed in the head of a page that tells search engines which version of a URL is the preferred one for indexing. It is written as <link rel="canonical" href="https://example.com/preferred-url/" /> and is invisible to users.
Canonical tags solve duplicate content problems without redirecting users. Common scenarios where they are needed include product pages accessible via multiple URL paths, filtered or sorted pages that generate parameter-based URLs, paginated content, and syndicated articles published on multiple domains.
Without a canonical tag on duplicate or near-duplicate pages, Google may split ranking signals across multiple versions or index the wrong one. The canonical tag does not guarantee Google will follow it. It is a strong hint, not a directive. If the canonical points to a page with significantly different content or one that is blocked by robots.txt, Google may ignore it. Implementing canonicals correctly requires checking that the preferred URL is indexable, loads correctly, and contains the content you want ranked.
