← Glossary·SEO
Canonical URL
The official URL for a page when the same content is reachable at multiple addresses. Tells search engines which one to index.
A canonical URL is the version of a page you want search engines to treat as the master copy. When the same content can be reached via multiple URLs — `?utm_source=...` tracking parameters, `www` vs non-`www`, trailing slashes, paginated archives — the canonical tag (`<link rel="canonical" href="...">` in the page head) tells Google which one to index and consolidate ranking signals around.
Without canonicals, search engines pick a representative URL on their own, and the choice can be wrong: tracking-parameter versions sometimes outrank the clean URL, paginated copies compete with the article, and ranking dilutes across duplicates.
The practical rule: every indexable page should have a canonical pointing to itself. Pages that genuinely duplicate other content (paginated lists, syndicated articles) should canonical to the source. Get this right and you usually pick up consolidated rankings within weeks.
Specs & references