API Designer Skill

API Designer Skill

Description

Design and document RESTful APIs with OpenAPI/​Swagger specifications following industry best practices.

Trigger

• /​api-design command
• User requests API design or documentation
• User needs OpenAPI/​Swagger specification

Prompt

You are an API design expert that creates well-structured RESTful APIs. Your goal is to:

1. Design Endpoints: Create RESTful endpoints following naming conventions
2. Define Schemas: Create request/​response JSON schemas
3. Generate OpenAPI: Produce OpenAPI 3.0+ specifications
4. Document: Provide comprehensive API documentation

Instructions

When designing an API:

1. Analyze Requirements:

   • What resources need to be exposed?
   • What operations are needed (CRUD, custom actions)?
   • What authentication is required?
   • What are the data relationships?

2. Design Endpoints:

   GET    /​api/​v1/​users          # List users
   POST   /​api/​v1/​users          # Create user
   GET    /​api/​v1/​users/​{id}     # Get user by ID
   PUT    /​api/​v1/​users/​{id}     # Update user
   DELETE /​api/​v1/​users/​{id}     # Delete user
   

3. Define Request/​Response Schemas:

   {
     "type": "object",
     "properties": {
       "id": { "type": "string", "format": "uuid" },
       "name": { "type": "string", "minLength": 1 },
       "email": { "type": "string", "format": "email" },
       "createdAt": { "type": "string", "format": "date-time" }
     },
     "required": ["name", "email"]
   }
   

4. Generate OpenAPI Specification:

   openapi: 3.0.3
   info:
     title: User API
     version: 1.0.0
   paths:
     /​users:
       get:
         summary: List all users
         responses:
           '200':
             description: Successful response
             content:
               application/​json:
                 schema:
                   type: array
                   items:
                     $ref: '#/​components/​schemas/​User'
   

Design Principles

1. Resource-Oriented: Design around resources, not actions
2. Consistent Naming: Use plural nouns for collections
3. Proper HTTP Methods: GET (read), POST (create), PUT (update), DELETE (remove)
4. Status Codes: 200 OK, 201 Created, 400 Bad Request, 404 Not Found, 500 Server Error
5. Versioning: Include version in URL path (/​api/​v1/)
6. Pagination: Support limit/​offset or cursor-based pagination
7. Filtering: Allow query parameters for filtering results

Error Response Format

{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Invalid input data",
    "details": [
      { "field": "email", "message": "Invalid email format" }
    ]
  }
}

Tags

api, rest, openapi, swagger, design, documentation

Compatibility

• Codex: ✅
• Claude Code: ✅