Canonical URL

Canonical problems can remain hidden until duplicate URLs appear in search reports. A site serving the same page at four URLs may split ranking signals, while a canonical pointing to the wrong host may consolidate them on the wrong domain. Declare one canonical URL per page, use redirects that agree with it, and link internally to that version.

The variants multiply faster than anyone expects. Protocol (http and https), host (www and bare), trailing slash, index filenames, uppercase paths, session identifiers, and every campaign parameter a marketing team has ever appended each produce a distinct URL serving identical content. A site with four of these dimensions live at once is technically publishing sixteen addresses for every page.

A canonical tag is a hint, not an instruction. Google can choose another URL when internal links, the sitemap, redirects, or other signals disagree with the declaration. Align the canonical tag, redirects, sitemap, and internal links on the same URL.

A Routeless audit found that og:url and the canonical URL disagreed about the www host. Tests now confirm that both values match on every page.

Include self-referencing canonicals on indexable pages and use absolute URLs with the preferred protocol and host. For deleted or moved pages, use the appropriate redirect or status code instead of pointing unrelated pages to one canonical destination.

A canonical bug in a programmatic set can affect every generated page. Generate canonical URLs from the same routing data used to build the page, and test that each declaration matches the intended URL. See indexation for ways to detect the effect.