Canonical URL
Also called rel=canonical, canonical link relation.
What Canonical URL means
A canonical URL is the address chosen to represent a piece of content when several addresses serve the same or nearly the same thing. Google defines canonicalization as "the process of selecting the representative canonical URL of a piece of content," and a canonical URL as the one "Google chose as the most representative from a set of duplicate pages."
More precisely
The `canonical` link relation is registered by RFC 6596, an Informational document from April 2012, which "specifies the preferred IRI from a set of resources that return the context IRI's content in duplicated form." Preference can be expressed with a link element, an HTTP Link header, redirects, sitemap entries and internal linking. Google treats all of them as signals: "indicating a canonical preference is a hint, not a rule," and it may select a different page.
Why it matters
Duplicate addresses split the signals that point at a page, and only one of them will be reported and shown. Where a page exists to be quoted, it needs one settled address rather than several equivalent ones.
Example
A product reachable at both a plain path and a version carrying tracking parameters declares the plain path as canonical so both resolve to a single representative URL.
Where this came from
Definitions here follow the specification or documentation that defines the term, not a paraphrase of another glossary.
-
RFC 6596: The Canonical Link Relation — IETF
The canonical link relation designates the preferred version of a resource and specifies the preferred IRI from a set of resources returning duplicated content. Informational, April 2012, by M. Ohye and J. Kupke.
Primary source · read 2026-09-03
-
What is URL canonicalization — Google
Google's definitions of canonicalization and of a canonical URL, and its statement that a declared canonical preference is a hint rather than a rule. Page last updated 2026-08-20 UTC.
Primary source · read 2026-09-03
developers.google.com/search/docs/crawling-indexing/canonicalization