Canonical URL Checker
Check a page's canonical tag without installing anything. Browsers can't fetch other websites (the CORS security rule), so you paste the page's HTML source and its URL. The checker finds every <link rel="canonical">, resolves it and flags the setups search engines ignore or misread. A second mode normalises a list of URLs into clean canonical form and merges duplicates.
Page
The address the HTML below is served from. Used to resolve relative links and spot mismatches.
In your browser, open the page, press Ctrl+U (Cmd+Option+U on a Mac), select all and paste. The <head> is enough.
Result
- Canonical (in head)
- /running-shoes
- resolves to https://example.com/running-shoes
Warning: Relative canonical URL
Relative canonicals are allowed but easy to break on staging hosts and mirrors. It resolves to https://example.com/running-shoes.
Warning: Trailing slash mismatch
The page URL has trailing slash, the canonical doesn't. Both work, but redirect one form to the other.
Warning: og:url differs from the canonical
og:url is https://example.com/running-shoes/. Social shares then count toward a different URL. Use the canonical URL in og:url.
<link rel="canonical" href="https://example.com/running-shoes">What it checks
From the pasted HTML and page URL the checker reports:
- Missing canonical, several canonicals, conflicting canonicals and an empty href.
- A canonical placed in the <body>, where Google ignores it.
- Relative and protocol-relative hrefs, resolved against the page URL or <base href>.
- http canonicals on https pages, cross-domain canonicals and www mismatches.
- Trailing slash and letter case differences between the canonical and the page URL.
- #fragments, tracking parameters (utm_*, gclid, fbclid) and other query strings in the canonical.
- An og:url that differs from the canonical, and noindex combined with a canonical.
It can't see canonicals sent as an HTTP Link header, redirects or robots.txt rules, because those aren't in the HTML. Check them with your crawler or the URL Inspection tool in Google Search Console.
How to use
- Open the page in your browser, view its source (Ctrl+U, or Cmd+Option+U on a Mac) and copy it.
- Paste the HTML and enter the URL the page is served from.
- Read the findings: problems first, then warnings, then what passes. Copy the suggested canonical tag if you need one.
- To clean up a list of URLs, switch to Normalise a URL list, pick your www and trailing slash conventions and copy the unique canonical URLs.
Why use this tool?
Frequently asked questions
What is the Canonical URL Checker?
A free in-browser tool that reads the rel=canonical tag in pasted HTML, resolves it against the page URL and flags configurations that search engines ignore or misread. It also normalises lists of URLs and merges duplicates.
Why do I paste the HTML instead of entering a URL?
Browsers block web pages from reading other sites (the CORS security rule), so a client-side tool can't download your page. Pasting the source also lets you check staging pages and pages behind a login. Canonicals sent as an HTTP Link header aren't in the HTML; check those with a crawler or Google Search Console.
Should every page have a self-referencing canonical?
For indexable pages, yes. A canonical pointing to the page's own clean URL tells search engines which version to index when parameters, tracking tags, http and https or www variants create duplicates. Point a canonical elsewhere only for genuine duplicates, such as print versions or syndicated copies.
Is it free?
Yes, the Canonical URL Checker is free with no signup required. It runs entirely in your browser, so nothing you paste is uploaded. Built by the Canvas Builder team.
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