Guide · Agent skill
How to use the Custom 404 Page Checker agent skill
Updated · written with AI from the project's own documentation and checked against our catalogue data
The 404-page skill teaches an AI agent to review a website's error handling for missing pages. It checks that a custom 404 page offers search, navigation and links to popular content, and that the server returns a real HTTP 404 status instead of a 200. This guide explains what the skill does, how to install it, how to trigger it with plain requests, and what to expect from its output.
Custom 404 Page Checkerthedaviddias/Front-End-Checklist · MIT Download the skill Quick start
- 1Download the ZIP. Download the skill ZIP from the page where you found this guide.
- 2Unzip the folder. Extract the 404-page folder so it contains SKILL.md and references/rule.md.
- 3Choose a location. Place the folder in ~/.claude/skills/ for personal use or in a project's .claude/skills/ folder.
- 4Or upload in the Claude apps. In the Claude apps, go to Settings → Capabilities → Skills and upload the skill.
- 5Ask a review question. Request a review of a template, rendered HTML or shared component that produces your 404 page.
- 6Check the status code. Ask the agent to confirm missing routes return HTTP 404 rather than 200.
- 7Apply the fixes. Review the flagged elements or routes and apply the suggested fixes.
What are agent skills and what does this one do?
An agent skill is a folder containing a SKILL.md file and optional reference files. When the skill is installed, an AI agent can load its instructions when your request matches the skill's description. This skill's description covers reviewing templates, rendered HTML, or shared components related to creating a custom 404 error page.
When triggered, the agent looks for a custom 404 page with search, navigation and links to popular content. It also confirms that the route returns HTTP 404 rather than a branded page with a 200 response, which search engines can treat as a soft 404. The agent then flags exact elements or routes that break the rule and suggests fixes.
- Checks for a custom 404 page with helpful navigation options
- Confirms missing routes return HTTP 404, not 200
- Flags exact elements, attributes and routes that violate the rule
- Suggests fixes such as adding search and links to important pages
How do you install the 404-page skill?
Download the ZIP file for the skill from the page where you found this guide. Unzip it so that the 404-page folder, containing SKILL.md and references/rule.md, sits in one of the locations below.
For a personal install across projects, place the folder in ~/.claude/skills/. For a single project, place it in that project's .claude/skills/ folder. If you use the Claude apps instead, upload the skill under Settings → Capabilities → Skills.
- Personal: ~/.claude/skills/404-page/
- Project: .claude/skills/404-page/ inside your project
- Claude apps: Settings → Capabilities → Skills, then upload the skill
How do you trigger the skill with natural requests?
You do not need a special command. Ask in plain language about templates, rendered HTML or shared components that produce a 404 page, and mention the error page or broken links. The skill's description is written around reviewing templates and rendered markup, so requests that name those things are the most likely to trigger it.
If the agent does not pick up the skill, name it directly, for example by saying you want the 404-page skill used.
- Review our 404 error page template for search and navigation.
- Check whether missing routes return a real 404 status or a soft 404.
- Review the rendered HTML of our error page and flag problems.
- Audit our shared error-page component before launch.
What should you provide to the agent?
The source does not list any required tools, scripts or packages. The skill is useful when the agent can read your templates and shared components, and when it can inspect the routes that handle missing pages. The status-code check needs access to the rendered routes, so the skill is less useful where server behaviour cannot be inspected.
Point the agent at the relevant files or the running site's routes. Give it the framework or template location if you know it, so it can find the markup that generates the 404 page.
- Access to your template, component or rendered HTML files
- Access to the routes that serve missing pages, for the status-code check
- No runtime requirements are listed for this skill
What are the safety notes for this skill?
According to the skill's listing, it does not run scripts and does not use the network. It works by reading and reviewing files and markup. Because the status-code check depends on the routes you give it, make sure the agent only inspects the environment you intend it to review.
- Runs scripts: no
- Uses network: no
- Licence: MIT
What tips help get useful results?
Ask for a review of a specific template or component rather than the whole site, so the agent can flag exact elements. Include the routes you know are missing pages so the status-code check has a concrete target.
Remember that the skill focuses on review and checklist guidance. For a fully designed 404 page, the skill is not the right tool, because its reference file is short and framework details are only summarised.
- Name the exact template or component under review
- List specific missing routes to test the 404 status
- Expect checklist-style feedback, not a finished design
What people use it for
- Reviewing a 404 template before a site launch
- Checking that broken links lead to a helpful page with search and navigation
- Auditing a shared error-page component for markup that breaks the rule
- Investigating SEO issues caused by soft 404 pages
Frequently asked questions
What is a soft 404?
A soft 404 is a missing page that shows an error-style message but returns a 200 OK status. The skill explains that search engines can treat these as soft 404s, which causes indexing problems. The fix is to make sure the server returns a real 404 status.
Is the 404-page skill free to use?
The skill is published under the MIT licence, according to its listing. The source does not mention pricing, so check the licence terms in the repository for details.
What do I need to run the 404-page skill?
The source lists no required tools, and the skill does not run scripts or use the network. You need access to the templates or rendered HTML you want reviewed, and access to the routes if you want the status code checked.
Can the skill build a 404 page for me?
Not as a main purpose. The skill focuses on review and checklist guidance rather than generating full designs. It can suggest fixes such as adding search and links to important pages.
Why does my agent not use the skill?
Check that the 404-page folder, with SKILL.md inside, is in ~/.claude/skills/ or the project's .claude/skills/ folder, or that you uploaded it under Settings → Capabilities → Skills. Then phrase your request around templates, rendered HTML or shared components, or name the skill directly.
How does this compare with other 404 page guides?
The source does not compare this skill with alternatives. It is narrower than a design tool: it reviews markup and status codes against a rule, and its reference file is short with framework details only summarised.
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Our verdict
Use this skill if you are a front-end developer or QA tester who wants an agent to review 404 templates and check that missing routes return a real 404 status. Pick something else if you need a finished 404 design or your server behaviour cannot be inspected, since the status-code check depends on access to the routes.
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