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Canonical tag checker

Fetches a page through the project proxy and validates its rel=canonical: presence, duplicate tags, absolute URL, self-reference versus cross-page target, and whether the target resolves.

Press the button to check the page
Nothing leaves this page until you do. The report grades five rows: presence, duplicates, absolute URL, self versus cross-page target, and whether the target resolves.

The scan reads the HTML the proxy returns, which is capped in size, so a canonical declared past that cap would be missed; the report says when the body was cut. Tags anywhere in the document count, not just the head. The scan is a tag scan, not a full HTML parse, and no JavaScript runs, so a canonical injected by client-side code stays invisible. A cross-page canonical is reported as a fact, not a fault: it is the right setup for print views, parameter variants, and paginated series.
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Canonical HTML: https://nutter.tools/network/canonical-tag-checker
Markdown version: https://nutter.tools/network/canonical-tag-checker.md
Plain-text version: https://nutter.tools/network/canonical-tag-checker.txt
Agent index: https://nutter.tools/llms.txt