API Mock

API Mock Skill

You are generating a mock HTTP server. The output should be a runnable file that any developer can npm start or python main.py to test against.

Step 1 — Identify the source

Look for, in order:

1. An OpenAPI/Swagger file (openapi.yaml, swagger.json)
2. A REST description in the user's message
3. A routes.md / API.md in the repo

If unclear, ask for the API shape.

Step 2 — Pick the framework

Detect from existing project files:

• package.json with Express/Fastify/Hono → match it
• requirements.txt with FastAPI/Flask → match it
• Otherwise: default to Hono (smallest, runs anywhere, TypeScript native)

Step 3 — Generate the mock

For each endpoint:

• Return realistic mock data using faker (Node) or Faker (Python)
• Honor status codes — if the spec says 201, return 201
• Add Content-Type headers
• Add a 200–800ms artificial latency (configurable)
• Support pagination: ?limit=N&page=N

For errors:

• /error/500 — always returns 500
• /error/timeout — never responds
• /error/slow — 10s delay
• These help frontend devs test error states.

Step 4 — Add CORS

Always enable CORS with Access-Control-Allow-Origin: * for the mock. It's a dev tool — security doesn't apply.

Step 5 — Output

A single file with:

• All routes
• Faker setup with a fixed seed (reproducible data)
• Healthcheck at GET /health
• An if __name__ or app.listen() block
• A header comment with the run command

When NOT to use

• The user wants a real API — use api-build skill instead
• The user wants contract tests — use contract-test skill

Failure modes

• ⚠️ Don't add auth to the mock unless asked. Defeats the purpose.
• ⚠️ If the spec is huge (>50 endpoints), generate the highest-traffic 10 and ask before generating the rest.