Guide · Agent skill
How to use the API Endpoint Builder agent skill
Updated · written with AI from the project's own documentation and checked against our catalogue data
The api-endpoint-builder skill is a set of instructions that tells an AI agent how to write a backend REST API route in a consistent way. It is for developers who have an Express or Fastify project and want new endpoints that include validation, authentication checks, standard status codes and documentation. After this guide you will know how to install the skill, how to ask for an endpoint so the agent uses it, and what to review before you use the code.
API Endpoint Buildersickn33/agentic-awesome-skills · MIT Download the skill Quick start
- 1Download the ZIP. Download the skill ZIP from this page. It contains README.md and SKILL.md.
- 2Unzip into a skills folder. Unzip it into ~/.claude/skills/ for personal use, or into .claude/skills/ in one project.
- 3Or upload it in the Claude apps. Open Settings, go to Capabilities, then Skills, and upload the skill.
- 4Open your backend project. Make sure you have a Node.js project using Express or Fastify, and a database client.
- 5Ask for an endpoint. Describe the resource, its fields, required checks and framework, for example 'Use @api-endpoint-builder to create a user registration endpoint'.
- 6Review the output. Check validation, authentication, status codes, the password handling and any tests before running the code.
What the skill makes the agent do
The skill tells the agent to build each endpoint from the same parts: a route definition with the correct HTTP method, input validation for the request body, params and query, authentication and authorization checks, the business logic, error handling, response formatting, API documentation and, if you ask, tests.
The skill includes Express and Fastify examples for the route definition, a validation function, a handler, a centralized error handler, pagination, filtering and a JSON documentation comment. The agent uses these as patterns, so the code it writes should look consistent from one endpoint to the next.
- Standard status codes: 200, 201, 204, 400, 401, 403, 404, 409 and 500
- A consistent response shape with success, data and error fields
- A security checklist covering auth, authorization, validation, parameterized queries, rate limiting, sensitive data and CORS
How to install the skill
Download the skill ZIP from this page. The skill folder contains README.md and SKILL.md. SKILL.md holds the instructions the agent reads.
To install it for your user account, unzip the download into ~/.claude/skills/. To install it for one project only, unzip it into the .claude/skills/ folder inside that project. You can also upload the skill in the Claude apps under Settings, then Capabilities, then Skills.
- Personal install: ~/.claude/skills/
- Project install: .claude/skills/ inside your project folder
- Claude apps: Settings → Capabilities → Skills, then upload
How to trigger the skill with a natural request
You do not need a special command. The SKILL.md file says the skill applies when you ask to create an API endpoint or build a REST API, or when your request mentions API, endpoint, route, REST or CRUD. The README also shows an explicit form you can use to be sure the skill is applied.
Give the agent the resource, the fields and the rules. Naming the framework (Express or Fastify) and whether you want tests helps the agent choose the matching examples.
- Name the framework: say Express or Fastify in the request
- Name the fields and which ones are required
- Say whether you want tests or documentation added
Use @api-endpoint-builder to create a user registration endpointExample: a user registration endpoint
For a request like the one above, the skill's examples point toward a POST route that runs an authentication check and then a validation function before the handler. The handler checks for an existing user, hashes the password, and returns 201 with the user data minus the password. Duplicate emails return 409, and unexpected errors return 500 with a generic message.
Treat this as a draft. The examples use a placeholder db object and a simple email and password check, so you will need to replace them with your own database client and your own security rules.
- Expect the route, validation, handler and documentation comment in one review set
- Check that the password is never returned in the response
- Check that the error handler does not expose details in production
router.post('/api/users', authenticate, validateUser, createUser);What you need and safety notes
The skill does not install Node.js, Express, Fastify or a database. You need a backend project and a database client that matches the code the agent writes. The skill is text guidance only: it does not run scripts and does not use the network, and it does not deploy or start a server.
The SKILL.md metadata lists the risk level as critical, which is a reason to review every generated file. The examples are generic scaffolds and may miss requirements specific to your stack, so have a person review authentication, authorization and data handling before production use.
- Requires: a Node.js backend project using Express or Fastify (implied by the examples)
- Runs scripts: no
- Uses network: no
- Examples are JavaScript only
Tips for better results
Ask for one resource at a time, such as users or orders, so the agent can keep the route, validation and handler consistent. Ask for the pagination and filtering patterns if your list endpoint needs them, since the skill includes examples for both.
Use the skill's own checklist as your review list after the agent finishes. Run the generated tests yourself, since the skill does not run them for you.
- Request tests explicitly if you want them; the skill includes them only when asked
- Review all auth and validation code by hand
- Adapt the examples if you do not use Express or Fastify
What people use it for
- Adding a user registration route with email, name and password validation
- Building CRUD routes for a resource such as orders or products in an existing Express app
- Adding a paginated list endpoint with a limit cap and an error for invalid page values
- Drafting a documentation comment and tests for an endpoint your team already plans to build
Frequently asked questions
How do I install the api-endpoint-builder skill?
Download the skill ZIP from this page and unzip it into ~/.claude/skills/ for personal use or into .claude/skills/ inside a project. You can also upload it in the Claude apps under Settings, then Capabilities, then Skills.
What do I need to use the API Endpoint Builder skill?
You need a backend project that uses Node.js with Express or Fastify, and a database client that fits the code the agent writes. The skill does not install these. The examples are JavaScript only.
Is the API Endpoint Builder skill free?
The skill is listed under the MIT licence. Check the licence file in the source repository for the full terms before you reuse or redistribute it.
Does the skill run code or deploy my API?
No. The skill is guidance for how the agent writes code. It does not run scripts, does not use the network, and does not deploy or start a server.
Can I use the generated code in production?
Only after a review. The examples are generic scaffolds, such as a simple email and password check and a placeholder db object, and may miss security requirements for your stack.
Why isn't the skill triggering when I ask for an API?
Include words such as API, endpoint, route, REST or CRUD in your request, or mention the skill by name with @api-endpoint-builder as shown in the README. Confirm the folder is in ~/.claude/skills/ or the project's .claude/skills/.
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Our verdict
Use this skill if you build Express or Fastify backends and want new endpoints written with the same validation, auth checks and status codes each time. Pick something else if you are not a developer, if you need code in another language, or if you need security-critical auth or payments code that you cannot review carefully.
Download the skill