API Documentation Generator

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 "Authorization: Bearer YOUR_TOKEN" \
 -H "Content-Type: application/json" \
 -d '{ "email": "user@example.com", "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: 'user@example.com', 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' }, json={
'email': 'user@example.com', 'password': 'SecurePass123!', 'name': 'John Doe' }
)

user = response.json() print(user) \`\`\`

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

2. Authentication

   • How to authenticate
   • Token management
   • Security best practices

3. Quick Start

   • Simple example to get started
   • Common use case walkthrough

4. Endpoints

   • Organized by resource
   • Full details for each endpoint

5. Data Models

   • Schema definitions
   • Field descriptions
   • Validation rules

6. Error Handling

   • Error code reference
   • Error response format
   • Troubleshooting guide

7. Rate Limiting

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

8. Changelog

   • API version history
   • Breaking changes
   • Deprecation notices

9. SDKs and Tools

   • Official client libraries
   • Postman collection
   • OpenAPI specification

Common Pitfalls

Problem: Documentation Gets Out of Sync

Symptoms: Examples don't work, parameters are wrong, endpoints return different data Solution:

• Generate docs from code comments/annotations
• Use tools like Swagger/OpenAPI
• Add API tests that validate documentation
• Review docs with every API change

Problem: Missing Error Documentation

Symptoms: Users don't know how to handle errors, support tickets increase Solution:

• Document every possible error code
• Provide clear error messages
• Include troubleshooting steps
• Show example error responses

Problem: Examples Don't Work

Symptoms: Users can't get started, frustration increases Solution:

• Test every code example
• Use real, working endpoints
• Include complete examples (not fragments)
• Provide a sandbox environment

Problem: Unclear Parameter Requirements

Symptoms: Users send invalid requests, validation errors Solution:

• Mark required vs optional clearly
• Document data types and formats
• Show validation rules
• Provide example values

Tools and Formats

OpenAPI/Swagger

Generate interactive documentation:

openapi: 3.0.0
info:
  title: My API
  version: 1.0.0
paths:
  /users:
    post:
      summary: Create a new user
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateUserRequest'

Postman Collection

Export collection for easy testing:

{
  "info": {
    "name": "My API",
    "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json"
  },
  "item": [
    {
      "name": "Create User",
      "request": {
        "method": "POST",
        "url": "{{baseUrl}}/api/v1/users"
      }
    }
  ]
}

Related Skills

• @doc-coauthoring - For collaborative documentation writing
• @copywriting - For clear, user-friendly descriptions
• @test-driven-development - For ensuring API behavior matches docs
• @systematic-debugging - For troubleshooting API issues

Additional Resources

• OpenAPI Specification
• REST API Best Practices
• GraphQL Documentation
• API Design Patterns
• Postman Documentation

Pro Tip: Keep your API documentation as close to your code as possible. Use tools that generate docs from code comments to ensure they stay in sync!