Check canonical tags that tell search engines the preferred URL for a page. Review rendered HTML and HTTP responses, identify missing or incorrect settings, and help correct duplicate-page signals caused by URL variations.
Use when auditing metadata, crawlability, structured data, or indexability related to Set canonical URLs for all pages. Verify the rendered HTML and HTTP response rather than relying only on source files.
canonical-url checks the canonical tags that tell search engines which URL to prefer, and helps fix missing tags or incorrect targets. When parameters or domain variations such as the presence or absence of www create multiple URLs for the same content, it reviews which URL should be canonical. It also checks for absolute URLs containing the protocol and domain, and for tags that point to the page itself. It identifies affected routes or templates and explains how to verify the final output.
Use it to review SEO settings page by page or examine a site where the same content is accessible through several URLs. It also helps check whether canonical URLs generated by a shared template are appropriate for each page.
Checks should cover generated HTML and HTTP responses, rather than source files alone. Treat canonical tags as settings that communicate a preferred URL to search engines, and verify their targets in the final page output.
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.
Duplicate content from URL parameters, www vs non-www, or pagination dilutes ranking signals—canonical tags consolidate these signals to the preferred URL.
Verify that this page has a canonical URL tag and that it points to the correct preferred version.
Add or correct the canonical URL tag in the head section to prevent duplicate content issues.
Explain how canonical URLs help search engines understand the preferred version of duplicate or similar pages.
Review metadata generation, rendered HTML, structured data, and response headers related to Set canonical URLs for all pages. 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-url
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Create and review custom 404 pages that help visitors recover from broken or moved links through search and navigation. Check the rendered page and HTTP response so missing content returns a proper 404 status.
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