API Documentation Generator

Overview

Automatically generate clear, comprehensive API documentation from your codebase. This skill helps you create professional documentation that includes endpoint descriptions, request/response examples, authentication details, error handling, and usage guidelines.

Perfect for REST APIs, GraphQL APIs, and WebSocket APIs.

When to Use This Skill

• Use when you need to document a new API
• Use when updating existing API documentation
• Use when your API lacks clear documentation
• Use when onboarding new developers to your API
• Use when preparing API documentation for external users
• Use when creating OpenAPI/Swagger specifications

How It Works

Step 1: Analyze the API Structure

Bind documentation to the actual source revision, routing/middleware/schema and verified examples. Mark missing or inferred behavior; do not invent rate limits, password policy, token expiry or exhaustive error coverage. Use synthetic data and secret placeholders. Public user creation must not accept an arbitrary client-supplied admin role: omit it unless a separately authorized admin endpoint validates that capability. Generated OpenAPI fragments need complete referenced schemas/responses and spec validation; interactive Try It calls are real operations requiring an approved sandbox.

First, I'll examine your API codebase to understand:

• Available endpoints and routes
• HTTP methods (GET, POST, PUT, DELETE, etc.)
• Request parameters and body structure
• Response formats and status codes
• Authentication and authorization requirements
• Error handling patterns

Step 2: Generate Endpoint Documentation

For each endpoint, I'll create documentation including:

Endpoint Details:

• HTTP method and URL path
• Brief description of what it does
• Authentication requirements
• Rate limiting information (if applicable)

Request Specification:

• Path parameters
• Query parameters
• Request headers
• Request body schema (with types and validation rules)

Response Specification:

• Success response (status code + body structure)
• Error responses (all possible error codes)
• Response headers

Code Examples:

• cURL command
• JavaScript/TypeScript (fetch/axios)
• Python (requests)
• Other languages as needed

Step 3: Add Usage Guidelines

I'll include:

• Getting started guide
• Authentication setup
• Common use cases
• Best practices
• Rate limiting details
• Pagination patterns
• Filtering and sorting options

Step 4: Document Error Handling

Clear error documentation including:

• All possible error codes
• Error message formats
• Troubleshooting guide
• Common error scenarios and solutions

Step 5: Create Interactive Examples

Where possible, I'll provide:

• Postman collection
• OpenAPI/Swagger specification
• Interactive code examples
• Sample responses

Examples

Example 1: REST API Endpoint Documentation

## Create User

Creates a new user account.

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

**Authentication:** Required (Bearer token)

**Request Body:**
\`\`\`json
{
  "email": "[email protected]",      // Required: Valid email address
  "password": "SecurePass123!",     // Required: Min 8 chars, 1 uppercase, 1 number
  "name": "John Doe",               // Required: 2-50 characters
  "role": "user"                    // Server-assigned output; do not accept admin from public registration
}
\`\`\`

**Success Response (201 Created):**
\`\`\`json
{
  "id": "usr_1234567890",
  "email": "[email protected]",
  "name": "John Doe",
  "role": "user",
  "createdAt": "2026-01-20T10:30:00Z",
  "emailVerified": false
}
\`\`\`

**Error Responses:**

- `400 Bad Request` - Invalid input data
  \`\`\`json
  {
    "error": "VALIDATION_ERROR",
    "message": "Invalid email format",
    "field": "email"
  }
  \`\`\`

- `409 Conflict` - Email already exists
  \`\`\`json
  {
    "error": "EMAIL_EXISTS",
    "message": "An account with this email already exists"
  }
  \`\`\`

- `401 Unauthorized` - Missing or invalid authentication token

**Example Request (cURL):**
\`\`\`bash
curl -X POST https://api.example.com/api/v1/users \
  -H "Authorization: Bearer YOUR_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "email": "[email protected]",
    "password": "SecurePass123!",
    "name": "John Doe"
  }'
\`\`\`

**Example Request (JavaScript):**
\`\`\`javascript
const response = await fetch('https://api.example.com/api/v1/users', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${token}`,
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    email: '[email protected]',
    password: 'SecurePass123!',
    name: 'John Doe'
  })
});

const user = await response.json();
console.log(user);
\`\`\`

**Example Request (Python):**
\`\`\`python
import requests

response = requests.post(
    'https://api.example.com/api/v1/users',
    headers={
        'Authorization': f'Bearer {token}',
        'Content-Type': 'application/json'
    },
    jso