api-documentation-generator skill

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

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": "user@example.com",      // Required: Valid email address
  "password": "SecurePass123!",     // Required: Min 8 chars, 1 uppercase, 1 number
  "name": "John Doe",               // Required: 2-50 characters
  "role": "user"                    // Optional: "user" or "admin" (default: "user")
}
\`\`\`

**Success Response (201 Created):**
\`\`\`json
{
  "id": "usr_1234567890",
  "email": "user@example.com",
  "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 "Aut

Example 2: GraphQL API Documentation

## User Query

Fetch user information by ID.

**Query:**
\`\`\`graphql
query GetUser($id: ID!) {
  user(id: $id) {
    id
    email
    name
    role
    createdAt
    posts {
      id
      title
      publishedAt
    }
  }
}
\`\`\`

**Variables:**
\`\`\`json
{
  "id": "usr_1234567890"
}
\`\`\`

**Response:**
\`\`\`json
{
  "data": {
    "user": {
      "id": "usr_1234567890",
      "email": "user@example.com",
      "name": "John Doe",
      "role": "user",
      "createdAt": "2026-01-20T10:30:00Z",
      "posts": [
        {
          "id": "post_123",
          "title": "My First Post",
          "publishedAt": "2026-01-21T14:00:00Z"
        }
      ]
    }
  }
}
\`\`\`

**Errors:**
\`\`\`json
{
  "errors": [
    {
      "message": "User not found",
      "extensions": {
        "code": "USER_NOT_FOUND",
        "userId": "usr_1234567890"
      }
    }
  ]
}
\`\`\`

Example 3: Authentication Documentation

## Authentication

All API requests require authentication using Bearer tokens.

### Getting a Token

**Endpoint:** `POST /api/v1/auth/login`

**Request:**
\`\`\`json
{
  "email": "user@example.com",
  "password": "your-password"
}
\`\`\`

**Response:**
\`\`\`json
{
  "token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...",
  "expiresIn": 3600,
  "refreshToken": "refresh_token_here"
}
\`\`\`

### Using the Token

Include the token in the Authorization header:

\`\`\`
Authorization: Bearer YOUR_TOKEN
\`\`\`

### Token Expiration

Tokens expire after 1 hour. Use the refresh token to get a new access token:

**Endpoint:** `POST /api/v1/auth/refresh`

**Request:**
\`\`\`json
{
  "refreshToken": "refresh_token_here"
}
\`\`\`

Best Practices

✅ Do This

• Be Consistent - Use the same format for all endpoints
• Include Examples - Provide working code examples in multiple languages
• Document Errors - List all possible error codes and their meanings
• Show Real Data - Use realistic example data, not "foo" and "bar"
• Explain Parameters - Describe what each parameter does and its constraints
• Version Your API - Include version numbers in URLs (/api/v1/)
• Add Timestamps - Show when documentation was last updated
• Link Related Endpoints - Help users discover related functionality
• Include Rate Limits - Document any rate limiting policies
• Provide Postman Collection - Make it easy to test your API

❌ Don't Do This

• Don't Skip Error Cases - Users need to know what can go wrong
• Don't Use Vague Descriptions - "Gets data" is not helpful
• Don't Forget Authentication - Always document auth requirements
• Don't Ignore Edge Cases - Document pagination, filtering, sorting
• Don't Leave Examples Broken - Test all code examples
• Don't Use Outdated Info - Keep documentation in sync with code
• Don't Overcomplicate - Keep it simple and scannable
• Don't Forget Response Headers - Document important headers

Documentation Structure

Recommended Sections

1. Introduction

• What the API does
• Base URL
• API version
• Support contact

1. Authentication

• How to authenticate
• Token management
• Security best practices

1. Quick Start

• Simple example to get started
• Common use case walkthrough

1. Endpoints

• Organized by resource
• Full details for each endpoint

1. Data Models

• Schema definitions
• Field descriptions
• Validation rules

1. Error Handling

• Error code reference
• Error response format
• Troubleshooting guide

1. Rate Limiting

• Limits and quotas
• Headers to check
• Handling rate limit errors

1. Changelog

• API version history
• Breaking changes
• Deprecation notices

1. SDKs and Tools