Canonical Tag
A rel="canonical" link that names the preferred URL for a page, telling search engines which version to index when duplicates exist.
A canonical tag is a <link rel="canonical"> element in a page's head that tells search engines the preferred (canonical) URL for that content. When the same or very similar content is reachable at several URLs — with tracking parameters, sort orders, session IDs, or http/https and www variants — the canonical tells engines which one to index and consolidate signals onto.
The safe default is a self-referential canonical: every page points to its own clean, absolute URL on a single host. Getting this wrong is costly. A canonical pointing at the wrong URL can deindex the page you wanted to keep, and using a canonical to point many distinct pages at one URL is a blunt instrument that can erase pages that were actually earning traffic.
A canonical is a hint, not a command — Google can and does override it if the signals disagree, reporting "Duplicate, Google chose different canonical" in Search Console. The reliable fix for duplication is to make each URL genuinely self-canonical and consistent with your sitemap and internal links, rather than papering over it with cross-canonicals.
Related terms
- 301 vs 302 vs 410 — Status codes for moved or removed pages: 301 permanent redirect, 302 temporary redirect, 410 gone. Each signals a different intent.
- Hreflang — Link annotations that tell search engines which language and region each version of a page targets, so the right one is served.
- Noindex — A directive that tells search engines to keep a page out of their index. The page must stay crawlable for the tag to be seen.
- XML Sitemap — A machine-readable list of the canonical, indexable URLs on a site, submitted to search engines to aid discovery.