How to use it
- 1
Paste the page address you need to check for canonicalization.
- 2
Run the check and wait for the WebDiag API response.
- 3
Compare canonical href, resolved canonical, and the final URL after redirects.
What the tool can do
- Safe HTML page fetching through the backend with SSRF protection and response size limits.
- Extracts the first link rel=canonical and resolves a relative href against the final URL.
- Shows final URL mismatch, host mismatch, noindex, and redirect count.
Common use cases
- Check whether canonical matches the final URL after HTTPS, www/non-www, or trailing slash redirects.
- Find pages without canonical after a migration, template change, or CMS release.
- Check for accidental noindex on an important landing page.
How it works inside
URL comparison normalizes host casing, default ports, trailing slash, and fragments.
A relative canonical is resolved through the final URL, but the recommendation flags it as less robust.
Questions and answers
Is a relative canonical an error?
Not always. Browsers and parsers can resolve it, but an absolute canonical is safer for diagnostics, migrations, and external signals.
Why should canonical match the final URL?
It reduces ambiguity for search engines: redirects, sitemap, internal links, and canonical point to the same preferred address.