Compare the preferred page URL declared in HTML canonical tags with the one sent in HTTP Link headers. Identify conflicting declarations, recommend consistent values, and explain how to verify the final page and response.
Use when auditing metadata, crawlability, structured data, or indexability related to Sync HTML canonical tags and Link headers. Verify the rendered HTML and HTTP response rather than relying only on source files.
Compare the rel="canonical" tag in HTML with the Link header in an HTTP response to check whether both declare exactly the same canonical URL. A canonical URL is the page address you want search engines to treat as the preferred version. The skill identifies routes or templates with conflicting declarations, suggests changes to the tag or header, and explains how to verify the output after the changes.
Use it to review a site that declares canonical URLs in both HTML and HTTP headers. It also helps you look for conflicting declarations when duplicate pages or unintended search indexing are a concern. The review compares the metadata generation process with the final output that reaches search engines, so you can locate the routes or templates responsible for a mismatch.
This comparison applies when both methods declare a canonical URL. Inspect the rendered HTML and actual HTTP response instead of relying only on source files. Conflicting declarations can cause search engines to ignore both.
This overview was written by AI (OpenAI Codex) from the public SKILL.md. Check the original below for the exact behavior.
AI rated this skill on four points using only the contents of its SKILL.md. Stars and popularity are not taken into account.
The total counts each point as A = 25, B = 15, C = 5. Rated by AI (OpenAI Codex) as of Oct 23, 2026. Treat it as a guide and read the original before installing.
Review the instructions the agent will receive before you install.
Conflicting canonical-url signals can lead search engines to ignore both declarations, potentially causing duplicate content issues and incorrect indexing.
rel="canonical" tag in your HTML matches the Link canonical-url header if both are usedCompare the HTML canonical tag with the HTTP Link header to ensure they point to the exact same URL.
Update either the HTML tag or the HTTP header so that they provide a consistent canonical URL signal.
Explain the risks of sending conflicting technical SEO signals to search engine crawlers.
Review metadata generation, rendered HTML, structured data, and response headers related to Sync HTML canonical tags and Link headers. Flag exact routes or templates where search-facing output violates the rule, and describe how to verify the final page output.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/rules/seo/canonical-header
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