Canonical Cross-Domain Detector

The canonical tag tells a search engine which URL represents that content. Pointing it at another domain is legitimate and exists for real cases — content republished with permission, the same shop on country domains, an article distributed through a partner portal. It is also one of the fastest ways to remove an entire site from the index without noticing.

Enter the page URL and paste the HTML: the page extracts the canonical tag, compares the domains and says whether it points within the same domain or outside it. When it points outside, the warning is blunt, because the effect is strong — you are asking the search engine to index the other address instead of yours, and the pointing page tends to vanish from results.

The cases where this goes wrong are well known. A botched migration leaving the old canonical aimed at the previous domain. A staging environment copied into production with the canonical frozen. A page template with a hardcoded address applied to every page. Periodic auditing pays off: a wrong canonical is silent and the effect shows up weeks later, once traffic has already fallen.