Guide · Agent skill
How to use the Canonical Header Checker agent skill
Updated · written with AI from the project's own documentation and checked against our catalogue data
The canonical-header skill is an instruction package that teaches an AI agent to check whether a page's canonical URL is declared consistently. It is useful for front-end developers, SEO specialists and teams reviewing templates that generate canonical tags. After this guide you will know what the skill does, how to install it, how to ask for it in plain language, and where its limits are.
Canonical Header Checkerthedaviddias/Front-End-Checklist · MIT Download the skill Quick start
- 1Download the ZIP. Download the canonical-header skill ZIP from this page.
- 2Unzip the skill. Unzip the archive so the canonical-header folder contains SKILL.md and references/rule.md.
- 3Place it in the skills folder. Move the folder to ~/.claude/skills/ for personal use, or to .claude/skills/ inside a project.
- 4Or upload it in the Claude apps. In the Claude apps, go to Settings → Capabilities → Skills and upload the ZIP.
- 5Ask a natural question. Name a specific URL or template and ask the agent to compare the canonical tag with the Link header.
- 6Review the result. Read the signals the agent found and decide which URL is correct before changing anything.
What the canonical-header skill makes the agent do
A canonical tag tells search engines which version of a page is the main one. A page can declare this in two places: a rel="canonical" tag in the HTML head, and a canonical Link header in the HTTP response. The skill focuses on whether those two declarations agree.
If they point to different URLs, search engines may ignore both, which can lead to duplicate content and indexing problems. The skill tells the agent to compare the HTML tag with the Link header, confirm they point to exactly the same URL, and suggest updating either one so the signals match. It also asks the agent to explain the risk of conflicting signals and to verify the final rendered output rather than only the source files.
- Compare the HTML canonical tag with the HTTP Link header
- Check that both point to the exact same URL
- Suggest a fix by updating either the HTML tag or the header
- Review metadata generation, rendered HTML, structured data and response headers
- Flag the exact routes or templates where output breaks the rule
Install the canonical-header skill
Download the skill ZIP from this page and unzip it. For a personal setup, place the unzipped folder in ~/.claude/skills/. For a single project, place it in that project's .claude/skills/ folder.
You can also upload the ZIP in the Claude apps under Settings → Capabilities → Skills.
- Personal install: ~/.claude/skills/
- Project install: .claude/skills/ inside your project
- Claude apps: Settings → Capabilities → Skills, then upload the ZIP
Trigger the skill with natural requests
You do not need a special command. The skill's description is written around auditing metadata, crawlability, structured data and indexability related to canonical tags and Link headers, so ask in those terms. Name the page or template you care about, because the agent needs a concrete target to verify.
Good requests describe the goal and the target. The agent should then fetch the live page, compare the two signals and report back.
- "Check whether the canonical tag and the canonical Link header match on https://example.com/pricing"
- "Audit the canonical handling in our product template and tell me which routes send conflicting signals"
- "My canonical tag points to the www version but the Link header points to the bare domain. Which one should change?"
Examples of what the agent checks and returns
The source gives this pattern as the correct state: the HTTP response header and the HTML tag name the same target URL. The agent should treat any mismatch as a problem to fix, and should verify the final rendered page, since templates and frameworks can change output after the source is written.
The skill does not define a report format or score. Expect a written review: the signals found, whether they match, a suggested change, and the template or route to look at.
- Good: Link header and HTML tag both point to https://example.com/target-page
- Problem: the HTML tag points to one URL and the Link header points to another
- Next step: decide which URL is correct, then update the other signal to match
# HTTP Response Header:
# Link: <https://example.com/target-page>; rel="canonical"
# HTML <head> section:
# <link rel="canonical" href="https://example.com/target-page">What the skill needs and what it does on your machine
The skill lists no required tools or dependencies. It does not run scripts, and it does not use the network according to its listing. The agent works from the instructions in SKILL.md and the reference file references/rule.md.
Verification does require the agent to request the live page and its headers. That is a network action performed by the agent during the task, so the skill is not suitable for sites where pages must not be fetched.
- Requires: nothing listed
- Runs scripts: no
- Uses network: no (verification of live pages requires requesting them)
- Files: SKILL.md and references/rule.md
Safety notes before you use it
Only point the agent at sites you are allowed to request. Fetching a live page and its headers is how the skill verifies output, so private, staging or sensitive pages may not be appropriate targets.
Review any suggested change before applying it. The skill suggests which signal to update, but the correct canonical URL depends on your site structure, and the agent cannot know that from the rule alone.
- Do not use it on private pages that must not be requested
- Confirm the intended canonical URL yourself before editing templates
- Treat the output as review guidance, not an automated audit
Tips for better results
Give the agent the exact URL or template path. Ask it to check the rendered output, not just the source file, because the skill itself emphasises this. If your site does not use canonical tags or Link headers, the rule does not apply, so skip this skill.
- Provide exact URLs or route and template names
- Ask for both the HTML tag and the HTTP header to be compared
- Re-run the check after any template or framework change
- Use it alongside a full crawler if you need site-wide scores; this skill does not report scores
What people use it for
- Checking a product or landing page where the HTML canonical and the HTTP Link header may disagree
- Reviewing a page template that generates canonical tags across many routes
- Preparing a site for search engine indexing by confirming canonical consistency before launch
- Explaining to a team why conflicting canonical signals can cause duplicate content issues
Frequently asked questions
What is the canonical-header skill?
It is an agent skill that teaches an AI agent to check whether a page's HTML rel="canonical" tag and its HTTP canonical Link header point to the same URL. If they disagree, the skill guides the agent to suggest a fix.
How do I install the canonical-header skill?
Download the ZIP from this page and unzip it into ~/.claude/skills/ for personal use or into a project's .claude/skills/ folder. You can also upload the ZIP in the Claude apps under Settings → Capabilities → Skills.
What does the skill require?
The listing states no required tools or dependencies. It runs no scripts, and according to its listing it does not use the network, although checking a live page means the agent requests it.
Is the canonical-header skill free?
The source is licensed under the MIT licence. Check the repository's licence file for the full terms before reuse.
Does the skill run a full SEO audit?
No. It gives the agent guidance and review steps for canonical consistency, but it does not crawl a site or report scores. For site-wide audits you would need a separate tool.
Can I use it on sites that do not use canonical tags?
No need. The rule only applies when canonical tags or Link headers are used, so sites without them do not benefit from this skill.
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Our verdict
Use this skill if you are a developer, SEO specialist or team reviewing canonical tags on existing pages and want an agent to spot mismatches between the HTML tag and the HTTP Link header. Pick a different tool if you need an automated site-wide crawl with scores, or if your pages must not be fetched.
Download the skill