Canonical Tag Checker

A canonical tag is an HTML <link rel="canonical"> element (or an HTTP header) that tells search engines which URL is the master version of a page when duplicate or near-duplicate content exists across multiple URLs. It is the primary mechanism for preventing duplicate content issues at scale.

Best practice: yes, on every indexable page. A self-referential canonical (where the canonical points to the page's own URL) reduces ambiguity, helps with parameter handling, and gives Google a definitive signal even when the URL has tracking parameters appended.

A canonical tag pointing to a different domain than the current page. This is sometimes legitimate (content syndication, E-E-A-T consolidation to a verified author profile) but is more often a sign of content theft, an old migration that wasn't completed, or accidental SEO harm. Worth investigating.

Yes — but search engines will ignore all of them and try to figure out the canonical themselves, which often leads to surprising results. Best practice: one canonical per page, period. If you have multiple, you've got a bug.

The audit runs entirely in your browser using a single fetch to /api/canonical-tag-check/check. We don't log URL contents, don't store responses, and don't train any AI on your data. Rate-limited to 30 checks/hour per IP.