Canonical Tag Checker
This free canonical tag checker loads a page and reads its rel=canonical link, the canonical HTTP header and og:url. It confirms there is exactly one canonical, that it is an absolute URL, that it references the page itself after redirects, that it matches og:url and does not conflict with noindex, and that the address it names answers 200. Each problem comes with a fix.
Canonical Tag Checker
On-page SEO
About this tool
The canonical tag tells search engines which address is the master copy of a page when the same content is reachable at several: with and without a trailing slash, with tracking parameters, over http and https, on a mobile subdomain. A wrong canonical is worse than none: it can hand a page's rankings to another URL, or to a 404, and the page quietly drops from the index while everything else looks fine.
The checker fetches the page as a crawler would, following redirects, and collects every canonical signal: link tags in the HTML, the Link header some servers send, and the Open Graph og:url tag that social networks use. It then runs the checks SEO audits always run: one canonical only, absolute rather than relative, pointing at the page itself (the final URL after redirects), same host and https, agreeing with og:url, not combined with noindex, and leading to a page that answers 200 without redirecting again.
A canonical that points elsewhere is not automatically wrong: paginated lists, syndicated articles and parameter versions should point at their master page. The tool flags those cases for review rather than failing them. It reads the HTML the server sends; canonical tags injected by JavaScript are not seen, which is also true of Google's first pass.
Frequently asked questions
Should every page have a self-referencing canonical?
Yes. Google recommends it, because it protects the page from tracking parameters, odd capitalisation and scraped copies claiming the content. The canonical should be the exact preferred address: same scheme, same host, same trailing-slash rule as the rest of the site.
What happens when there are two canonical tags?
Google ignores both and chooses for itself, so the tag does nothing. Two tags usually come from an SEO plugin and a theme both adding one. Remove one source so that a single rel=canonical remains.
Can a canonical URL be relative?
Technically yes, but Google advises against it: a relative canonical is resolved against the page address, so a scraped or misconfigured copy resolves it to the wrong domain. Always write the full absolute URL, https included.
Is it a problem if og:url and the canonical differ?
Usually it is a sign that one of them is stale, often after a domain or https move. Search engines use the canonical, social networks use og:url, and both should name the same preferred address so shares and rankings accumulate on one URL.
Can I use a canonical tag together with noindex?
No. A noindex tells Google to drop the page and a canonical asks it to pass signals to another page; Google has said the combination is contradictory and it may ignore the canonical. Use one or the other: canonical for duplicates you want consolidated, noindex for pages that should not appear at all.