api-documentation

What this skill does

# API Documentation


## When to use this skill

- **API Development**: When adding new endpoints
- **External Release**: Public API launch
- **Team Collaboration**: Frontend-backend interface definition

## Instructions

### Step 1: OpenAPI (Swagger) Spec

```yaml
openapi: 3.0.0
info:
  title: User Management API
  version: 1.0.0
  description: API for managing users
  contact:
    email: [email protected]

servers:
  - url: https://api.example.com/v1
    description: Production
  - url: https://staging-api.example.com/v1
    description: Staging

paths:
  /users:
    get:
      summary: List all users
      description: Retrieve a paginated list of users
      tags:
        - Users
      parameters:
        - name: page
          in: query
          schema:
            type: integer
            default: 1
        - name: limit
          in: query
          schema:
            type: integer
            default: 20
            maximum: 100
      responses:
        '200':
          description: Successful response
          content:
            application/json:
              schema:
                type: object
                properties:
                  data:
                    type: array
                    items:
                      $ref: '#/components/schemas/User'
                  pagination:
                    $ref: '#/components/schemas/Pagination'
        '401':
          $ref: '#/components/responses/Unauthorized'

    post:
      summary: Create a new user
      tags:
        - Users
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateUserRequest'
      responses:
        '201':
          description: User created
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/User'
        '400':
          $ref: '#/components/responses/BadRequest'

components:
  schemas:
    User:
      type: object
      properties:
        id:
          type: string
          format: uuid
        email:
          type: string
          format: email
        name:
          type: string
        createdAt:
          type: string
          format: date-time
      required:
        - id
        - email
        - name

    CreateUserRequest:
      type: object
      properties:
        email:
          type: string
          format: email
        name:
          type: string
          minLength: 2
          maxLength: 50
        password:
          type: string
          minLength: 8
      required:
        - email
        - name
        - password

    Pagination:
      type: object
      properties:
        page:
          type: integer
        limit:
          type: integer
        total:
          type: integer

  responses:
    Unauthorized:
      description: Unauthorized
      content:
        application/json:
          schema:
            type: object
            properties:
              error:
                type: string
                example: "Authentication required"

    BadRequest:
      description: Bad Request
      content:
        application/json:
          schema:
            type: object
            properties:
              error:
                type: string
                example: "Invalid input"

  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      bearerFormat: JWT

security:
  - bearerAuth: []
```

### Step 2: Generate Documentation from Code (JSDoc/Decorators)

**Express + TypeScript**:
```typescript
/**
 * @swagger
 * /api/users:
 *   post:
 *     summary: Create a new user
 *     tags: [Users]
 *     requestBody:
 *       required: true
 *       content:
 *         application/json:
 *           schema:
 *             type: object
 *             required:
 *               - email
 *               - name
 *               - password
 *             properties:
 *               email:
 *                 type: string
 *                 format: email
 *               name:
 *                 type: string
 *               password:
 *                 type: string
 *                 minLength: 8
 *     responses:
 *       201:
 *         description: User created successfully
 *       400:
 *         description: Invalid input
 */
router.post('/users', async (req, res) => {
  const { email, name, password } = req.body;
  const user = await userService.createUser({ email, name, password });
  res.status(201).json(user);
});
```

### Step 3: Interactive Documentation

**Swagger UI Setup**:
```typescript
import swaggerUi from 'swagger-ui-express';
import YAML from 'yamljs';

const swaggerDocument = YAML.load('./openapi.yaml');

app.use('/api-docs', swaggerUi.serve, swaggerUi.setup(swaggerDocument, {
  customCss: '.swagger-ui .topbar { display: none }',
  customSiteTitle: "My API Documentation"
}));
```

### Step 4: Examples & Guides

```markdown
## API Documentation

### Authentication

All API requests require authentication using JWT tokens.

#### Getting a Token
\`\`\`bash
curl -X POST https://api.example.com/v1/auth/login \
  -H "Content-Type: application/json" \
  -d '{"email": "[email protected]", "password": "yourpassword"}'
\`\`\`

Response:
\`\`\`json
{
  "accessToken": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...",
  "refreshToken": "..."
}
\`\`\`

#### Using the Token
\`\`\`bash
curl -X GET https://api.example.com/v1/users \
  -H "Authorization: Bearer YOUR_ACCESS_TOKEN"
\`\`\`

### Creating a User

**Endpoint**: `POST /v1/users`

**Request Body**:
\`\`\`json
{
  "email": "[email protected]",
  "name": "John Doe",
  "password": "SecurePass123!"
}
\`\`\`

**Success Response** (201):
\`\`\`json
{
  "id": "123e4567-e89b-12d3-a456-426614174000",
  "email": "[email protected]",
  "name": "John Doe",
  "createdAt": "2025-01-15T10:00:00Z"
}
\`\`\`

**Error Response** (400):
\`\`\`json
{
  "error": "Email already exists"
}
\`\`\`

### Rate Limiting
- 100 requests per 15 minutes per IP
- Header: `X-RateLimit-Remaining`

### Pagination
\`\`\`
GET /v1/users?page=2&limit=20
\`\`\`

Response includes pagination info:
\`\`\`json
{
  "data": [...],
  "pagination": {
    "page": 2,
    "limit": 20,
    "total": 157,
    "pages": 8
  }
}
\`\`\`

### Error Codes
- `400` - Bad Request (validation error)
- `401` - Unauthorized (missing/invalid token)
- `403` - Forbidden (insufficient permissions)
- `404` - Not Found
- `409` - Conflict (duplicate resource)
- `429` - Too Many Requests (rate limit)
- `500` - Internal Server Error
```

## Output format

### API Documentation Structure

```
docs/
├── README.md                    # Overview
├── getting-started.md           # Quick start guide
├── authentication.md            # Auth guide
├── api-reference/
│   ├── users.md                 # Users endpoints
│   ├── auth.md                  # Auth endpoints
│   └── products.md              # Products endpoints
├── guides/
│   ├── pagination.md
│   ├── error-handling.md
│   └── rate-limiting.md
├── examples/
│   ├── curl.md
│   ├── javascript.md
│   └── python.md
└── openapi.yaml                 # OpenAPI spec
```

## Constraints

### Required Rules (MUST)

1. **Real Examples**: Provide working code examples
2. **Error Cases**: Document not only success but also failure cases
3. **Keep Updated**: Update documentation when API changes

### Prohibited (MUST NOT)

1. **Real Keys in Examples**: Do not use real API keys/passwords in examples
2. **Vague Descriptions**: Unclear descriptions like "returns data"

## Best practices

1. **Try It Out**: Provide interactive documentation (Swagger UI)
2. **Provide SDK**: SDK and examples for major languages
3. **Changelog**: Document API changes

## References

- [OpenAPI Specification](https://swagger.io/specification/)
- [Swagger UI](https://swagger.io/tools/swagger-ui/)
- [Redoc](https://redocly.com/)

## Metadata

### Version
- **Current Version**: 1.0.0
- **Last Updated**: 2025-01-01
- **Compatible Platforms**: Claude, ChatGPT, Gemi