Canonical URL
Also called rel=canonical, canonical tag
The URL a site declares to be the preferred address for a piece of content, using a rel=canonical link. It consolidates duplicate or near-duplicate URLs so that ranking signals accrue to one address instead of being split.
A canonical says: of the several URLs that serve this content, this is the one that counts. Tracking parameters, print views, session IDs, HTTP and HTTPS, with and without a trailing slash — all of them can serve the same page, and without a canonical the signals split across them.
It is a hint. Search engines usually honour a canonical and sometimes overrule it, typically when the declared canonical is clearly not equivalent to the page declaring it.
Self-referencing canonicals are correct. A page that is its own canonical should say so. It costs nothing and removes ambiguity.
The failure mode is severe. A canonical pointing at the wrong page — a template-wide canonical to the homepage is the classic — tells the engine every page on the site is the homepage. Pages disappear from results without any obvious error. This is exactly the class of finding a site audit exists to catch, and it is why netweft classifies it as high severity rather than as one line among four hundred.
Last reviewed . Also served as markdown at /glossary/canonical-url.md.