name: api-documentation description: Document REST APIs with OpenAPI/Swagger specifications, endpoint documentation, authentication, error handling, and SDK guides. Use for API reference docs, Swagger specs, and client library documentation. Triggers: api docs, openapi, swagger, endpoint documentation, rest api, api reference, sdk documentation, api specification, document api, api endpoints.

API Documentation

Overview

Comprehensive API documentation skill covering OpenAPI/Swagger specifications, endpoint documentation, authentication flows, error handling, versioning strategies, and SDK/client documentation.

Instructions

1. Understand the API First

• Review all endpoints and their purposes
• Identify authentication mechanisms
• Understand request/response schemas
• Note error conditions and edge cases
• Check existing API patterns for consistency

2. Documentation Components

Every API should document:

1. Authentication: How to authenticate
2. Base URL: Environment-specific URLs
3. Endpoints: All available operations
4. Schemas: Request/response models
5. Errors: Error codes and handling
6. Rate limits: Throttling policies
7. Versioning: How versions work

Best Practices

• Use consistent terminology
• Provide working examples for every endpoint
• Document all possible response codes
• Include request/response examples
• Explain authentication clearly
• Document rate limits and quotas
• Keep schemas DRY with $ref

Examples

OpenAPI/Swagger Specification

openapi: 3.1.0
info:
  title: User Management API
  description: |
    API for managing users and their profiles.

    ## Authentication
    All endpoints require Bearer token authentication.
    Obtain a token via POST /auth/login.

    ## Rate Limits
    - Standard: 100 requests/minute
    - Authenticated: 1000 requests/minute
  version: 2.0.0
  contact:
    name: API Support
    email: api-support@example.com
    url: https://developer.example.com
  license:
    name: MIT
    url: https://opensource.org/licenses/MIT

servers:
  - url: https://api.example.com/v2
    description: Production
  - url: https://api.staging.example.com/v2
    description: Staging
  - url: http://localhost:3000/v2
    description: Local development

tags:
  - name: Users
    description: User management operations
  - name: Authentication
    description: Authentication and authorization

security:
  - BearerAuth: []

paths:
  /users:
    get:
      summary: List all users
      description: |
        Retrieve a paginated list of users.
        Results are sorted by creation date (newest first).
      operationId: listUsers
      tags:
        - Users
      parameters:
        - $ref: "#/components/parameters/PageParam"
        - $ref: "#/components/parameters/LimitParam"
        - name: status
          in: query
          description: Filter by user status
          schema:
            type: string
            enum: [active, inactive, pending]
        - name: search
          in: query
          description: Search by name or email
          schema:
            type: string
            minLength: 2
      responses:
        "200":
          description: Successful response
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/UserListResponse"
              example:
                data:
                  - id: "usr_123"
                    email: "john@example.com"
                    name: "John Doe"
                    status: "active"
                    createdAt: "2024-01-15T10:30:00Z"
                pagination:
                  page: 1
                  limit: 20
                  total: 150
                  hasMore: true
        "401":
          $ref: "#/components/responses/Unauthorized"
        "429":
          $ref: "#/components/responses/RateLimited"

    post:
      summary: Create a new user
      description: Create a new user account
      operationId: createUser
      tags:
        - Users
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: "#/components/schemas/CreateUserRequest"
            examples:
              basic:
                summary: Basic user creation
                value:
                  email: "jane@example.com"
                  name: "Jane Smith"
                  password: "secureP@ssw0rd"
              withRole:
                summary: User with admin role
                value:
                  email: "admin@example.com"
                  name: "Admin User"
                  password: "secureP@ssw0rd"
                  role: "admin"
      responses:
        "201":
          description: User created successfully
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/UserResponse"
        "400":
          $ref: "#/components/responses/BadRequest"
        "409":
          description: User with this email already exists
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/Error"
              example:
                error:
                  code: "USER_EXISTS"
                  message: "A user with this email already exists"

  /users/{userId}:
    get:
      summary: Get user by ID
      description: Retrieve a specific user by their unique identifier
      operationId: getUserById
      tags:
        - Users
      parameters:
        - $ref: "#/components/parameters/UserIdParam"
      responses:
        "200":
          description: Successful response
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/UserResponse"
        "404":
          $ref: "#/components/responses/NotFound"

    patch:
      summary: Update user
      description: Update user properties. Only provided fields are updated.
      operationId: updateUser
      tags:
        - Users
      parameters:
        - $ref: "#/components/parameters/UserIdParam"
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: "#/components/schemas/UpdateUserRequest"
      responses:
        "200":
          description: User updated successfully
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/UserResponse"
        "400":
          $ref: "#/components/responses/BadRequest"
        "404":
          $ref: "#/components/responses/NotFound"

    delete:
      summary: Delete user
      description: Permanently delete a user account
      operationId: deleteUser
      tags:
        - Users
      parameters:
        - $ref: "#/components/parameters/UserIdParam"
      responses:
        "204":
          description: User deleted successfully
        "404":
          $ref: "#/components/responses/NotFound"

components:
  securitySchemes:
    BearerAuth:
      type: http
      scheme: bearer
      bearerFormat: JWT
      description: |
        JWT token obtained from POST /auth/login.
        Include in header: `Authorization: Bearer <token>`

    ApiKeyAuth:
      type: apiKey
      in: header
      name: X-API-Key
      description: API key for server-to-server authentication

  parameters:
    UserIdParam:
      name: userId
      in: path
      required: true
      description: Unique user identifier
      schema:
        type: string
        pattern: "^usr_[a-zA-Z0-9]+$"
      example: usr_123abc

    PageParam:
      name: page
      in: query
      description: Page number (1-indexed)
      schema:
        type: integer
        minimum: 1
        default: 1

    LimitParam:
      name: limit
      in: query
      description: Number of items per page
      schema:
        type: integer
        minimum: 1
        maximum: 100
        default: 20

  schemas:
    User:
      type: object
      required:
        - id
        - email
        - name
        - status
        - createdAt
      properties:
        id:
          type: string
          description: Unique identifier
          example: usr_123abc
        email:
          type: string
          format: email
          description: User's email address
          example: john@example.com
        name:
          type: string
          description: User's full name
          example: John Doe
        status:
          type: string
          enum: [active, inactive, pending]
          description: Account status
        role:
          type: string
          enum: [user, admin, moderator]
          default: user
        createdAt:
          type: string
          format: date-time
          description: Account creation timestamp
        updatedAt:
          type: string
          format: date-time
          description: Last update timestamp

    CreateUserRequest:
      type: object
      required:
        - email
        - name
        - password
      properties:
        email:
          type: string
          format: email
        name:
          type: string
          minLength: 2
          maxLength: 100
        password:
          type: string
          format: password
          minLength: 8
          description: Must contain uppercase, lowercase, number, and special character
        role:
          type: string
          enum: [user, admin, moderator]
          default: user

    UpdateUserRequest:
      type: object
      minProperties: 1
      properties:
        name:
          type: string
          minLength: 2
          maxLength: 100
        status:
          type: string
          enum: [active, inactive]

    UserResponse:
      type: object
      properties:
        data:
          $ref: "#/components/schemas/User"

    UserListResponse:
      type: object
      properties:
        data:
          type: array
          items:
            $ref: "#/components/schemas/User"
        pagination:
          $ref: "#/components/schemas/Pagination"

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

    Error:
      type: object
      properties:
        error:
          type: object
          properties:
            code:
              type: string
              description: Machine-readable error code
            message:
              type: string
              description: Human-readable error message
            details:
              type: array
              items:
                type: object
                properties:
                  field:
                    type: string
                  message:
                    type: string

  responses:
    BadRequest:
      description: Invalid request parameters
      content:
        application/json:
          schema:
            $ref: "#/components/schemas/Error"
          example:
            error:
              code: "VALIDATION_ERROR"
              message: "Request validation failed"
              details:
                - field: "email"
                  message: "Must be a valid email address"

    Unauthorized:
      description: Authentication required
      content:
        application/json:
          schema:
            $ref: "#/components/schemas/Error"
          example:
            error:
              code: "UNAUTHORIZED"
              message: "Invalid or missing authentication token"

    NotFound:
      description: Resource not found
      content:
        application/json:
          schema:
            $ref: "#/components/schemas/Error"
          example:
            error:
              code: "NOT_FOUND"
              message: "The requested resource was not found"

    RateLimited:
      description: Rate limit exceeded
      headers:
        X-RateLimit-Limit:
          schema:
            type: integer
          description: Request limit per minute
        X-RateLimit-Remaining:
          schema:
            type: integer
          description: Remaining requests
        X-RateLimit-Reset:
          schema:
            type: integer
          description: Unix timestamp when limit resets
      content:
        application/json:
          schema:
            $ref: "#/components/schemas/Error"
          example:
            error:
              code: "RATE_LIMITED"
              message: "Too many requests. Please retry after 60 seconds."

Endpoint Documentation (Markdown)

## Create User

Create a new user account in the system.

**Endpoint:** `POST /users`

**Authentication:** Required (Bearer token)

### Request

#### Headers

| Header        | Required | Description                           |
| ------------- | -------- | ------------------------------------- |
| Authorization | Yes      | Bearer token                          |
| Content-Type  | Yes      | `application/json`                    |
| X-Request-Id  | No       | Unique request identifier for tracing |

#### Body Parameters

| Parameter | Type   | Required | Description                                                                     |
| --------- | ------ | -------- | ------------------------------------------------------------------------------- |
| email     | string | Yes      | Valid email address                                                             |
| name      | string | Yes      | Full name (2-100 characters)                                                    |
| password  | string | Yes      | Password (min 8 chars, must include uppercase, lowercase, number, special char) |
| role      | string | No       | User role: `user`, `admin`, `moderator`. Default: `user`                        |

#### Example Request

\`\`\`bash
curl -X POST https://api.example.com/v2/users \
 -H "Authorization: Bearer eyJhbG..." \
 -H "Content-Type: application/json" \
 -d '{
"email": "jane@example.com",
"name": "Jane Smith",
"password": "SecureP@ss123"
}'
\`\`\`

### Response

#### Success Response (201 Created)

\`\`\`json
{
"data": {
"id": "usr_abc123",
"email": "jane@example.com",
"name": "Jane Smith",
"status": "pending",
"role": "user",
"createdAt": "2024-01-15T10:30:00Z"
}
}
\`\`\`

#### Error Responses

| Status | Code             | Description              |
| ------ | ---------------- | ------------------------ |
| 400    | VALIDATION_ERROR | Invalid request body     |
| 401    | UNAUTHORIZED     | Missing or invalid token |
| 409    | USER_EXISTS      | Email already registered |
| 429    | RATE_LIMITED     | Too many requests        |

**400 Bad Request:**
\`\`\`json
{
"error": {
"code": "VALIDATION_ERROR",
"message": "Request validation failed",
"details": [
{
"field": "password",
"message": "Password must be at least 8 characters"
}
]
}
}
\`\`\`

Authentication Documentation

# Authentication

## Overview

The API supports two authentication methods:

1. **Bearer Token (JWT)** - For user-facing applications
2. **API Key** - For server-to-server integrations

## Bearer Token Authentication

### Obtaining a Token

\`\`\`bash
POST /auth/login
Content-Type: application/json

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

**Response:**
\`\`\`json
{
"accessToken": "eyJhbGciOiJIUzI1NiIs...",
"refreshToken": "dGhpcyBpcyBhIHJlZnJl...",
"expiresIn": 3600,
"tokenType": "Bearer"
}
\`\`\`

### Using the Token

Include the token in the Authorization header:

\`\`\`
Authorization: Bearer eyJhbGciOiJIUzI1NiIs...
\`\`\`

### Token Lifecycle

| Token         | Lifetime | Usage                   |
| ------------- | -------- | ----------------------- |
| Access Token  | 1 hour   | API requests            |
| Refresh Token | 30 days  | Obtain new access token |

### Refreshing Tokens

\`\`\`bash
POST /auth/refresh
Content-Type: application/json

{
"refreshToken": "dGhpcyBpcyBhIHJlZnJl..."
}
\`\`\`

## API Key Authentication

For server-to-server integrations, use API key authentication.

### Creating an API Key

1. Go to Dashboard > Settings > API Keys
2. Click "Create New Key"
3. Select permissions and expiration
4. Copy and securely store the key

### Using the API Key

Include in the `X-API-Key` header:

\`\`\`
X-API-Key: sk_live_abc123...
\`\`\`

### API Key Best Practices

- Never expose keys in client-side code
- Rotate keys regularly (every 90 days)
- Use separate keys for each environment
- Apply minimum required permissions

Error Response Documentation

# Error Handling

## Error Response Format

All errors follow a consistent format:

\`\`\`json
{
"error": {
"code": "ERROR_CODE",
"message": "Human-readable description",
"details": [
{
"field": "fieldName",
"message": "Field-specific error"
}
],
"requestId": "req_abc123"
}
}
\`\`\`

## HTTP Status Codes

| Status | Meaning           | When Used                               |
| ------ | ----------------- | --------------------------------------- |
| 200    | OK                | Successful GET, PUT, PATCH              |
| 201    | Created           | Successful POST creating resource       |
| 204    | No Content        | Successful DELETE                       |
| 400    | Bad Request       | Invalid request syntax or parameters    |
| 401    | Unauthorized      | Missing or invalid authentication       |
| 403    | Forbidden         | Valid auth but insufficient permissions |
| 404    | Not Found         | Resource doesn't exist                  |
| 409    | Conflict          | Resource state conflict                 |
| 422    | Unprocessable     | Valid syntax but semantic errors        |
| 429    | Too Many Requests | Rate limit exceeded                     |
| 500    | Internal Error    | Server-side error                       |

## Common Error Codes

### Authentication Errors

| Code               | HTTP Status | Description            | Resolution                   |
| ------------------ | ----------- | ---------------------- | ---------------------------- |
| UNAUTHORIZED       | 401         | No token provided      | Include Authorization header |
| TOKEN_EXPIRED      | 401         | Token has expired      | Refresh your access token    |
| TOKEN_INVALID      | 401         | Token is malformed     | Obtain a new token           |
| INSUFFICIENT_SCOPE | 403         | Token lacks permission | Request with proper scopes   |

### Validation Errors

| Code             | HTTP Status | Description               | Resolution                          |
| ---------------- | ----------- | ------------------------- | ----------------------------------- |
| VALIDATION_ERROR | 400         | Request failed validation | Check `details` for specific fields |
| INVALID_JSON     | 400         | Malformed JSON body       | Verify JSON syntax                  |
| MISSING_FIELD    | 400         | Required field missing    | Include all required fields         |

### Resource Errors

| Code            | HTTP Status | Description            | Resolution             |
| --------------- | ----------- | ---------------------- | ---------------------- |
| NOT_FOUND       | 404         | Resource doesn't exist | Verify resource ID     |
| ALREADY_EXISTS  | 409         | Duplicate resource     | Use unique identifiers |
| RESOURCE_LOCKED | 423         | Resource is locked     | Wait and retry         |

## Handling Errors in Code

### JavaScript/TypeScript

\`\`\`typescript
try {
const response = await api.createUser(userData);
} catch (error) {
if (error.status === 401) {
await refreshToken();
return retry();
}

if (error.status === 429) {
const retryAfter = error.headers['retry-after'];
await sleep(retryAfter \* 1000);
return retry();
}

if (error.body?.error?.code === 'VALIDATION_ERROR') {
const fieldErrors = error.body.error.details;
displayFieldErrors(fieldErrors);
}
}
\`\`\`

Versioning Documentation

# API Versioning

## Version Format

The API uses URL path versioning:

\`\`\`
https://api.example.com/v{major}/resource
\`\`\`

Current version: **v2**

## Supported Versions

| Version | Status     | Sunset Date |
| ------- | ---------- | ----------- |
| v2      | Current    | -           |
| v1      | Deprecated | 2024-12-31  |

## Version Lifecycle

1. **Current**: Actively developed and supported
2. **Deprecated**: Supported but no new features
3. **Sunset**: Read-only access for 90 days
4. **Retired**: No longer accessible

## Breaking vs Non-Breaking Changes

### Non-Breaking (No version bump)

- Adding new endpoints
- Adding optional parameters
- Adding new response fields
- Adding new enum values

### Breaking (Major version bump)

- Removing endpoints
- Removing or renaming fields
- Changing field types
- Changing authentication method
- Changing error format

## Migration Guide: v1 to v2

### Authentication Change

**v1:** API Key in query parameter
\`\`\`
GET /v1/users?api_key=abc123
\`\`\`

**v2:** Bearer token in header
\`\`\`
GET /v2/users
Authorization: Bearer eyJhbG...
\`\`\`

### Response Format Change

**v1:** Flat response
\`\`\`json
{
"id": "123",
"name": "John"
}
\`\`\`

**v2:** Wrapped response
\`\`\`json
{
"data": {
"id": "usr_123",
"name": "John"
}
}
\`\`\`

SDK Documentation

# JavaScript SDK

## Installation

\`\`\`bash
npm install @example/api-client
\`\`\`

## Quick Start

\`\`\`javascript
import { ApiClient } from '@example/api-client';

const client = new ApiClient({
apiKey: process.env.API_KEY,
environment: 'production' // or 'sandbox'
});

// Create a user
const user = await client.users.create({
email: 'jane@example.com',
name: 'Jane Smith'
});

console.log(user.id); // usr_abc123
\`\`\`

## Configuration

\`\`\`javascript
const client = new ApiClient({
// Required
apiKey: 'sk*live*...',

// Optional
environment: 'production', // 'production' | 'sandbox'
timeout: 30000, // Request timeout in ms
retries: 3, // Auto-retry failed requests
logger: console, // Custom logger
});
\`\`\`

## Resources

### Users

\`\`\`javascript
// List users with pagination
const { data, pagination } = await client.users.list({
page: 1,
limit: 20,
status: 'active'
});

// Get single user
const user = await client.users.get('usr_123');

// Create user
const newUser = await client.users.create({
email: 'new@example.com',
name: 'New User'
});

// Update user
const updated = await client.users.update('usr_123', {
name: 'Updated Name'
});

// Delete user
await client.users.delete('usr_123');
\`\`\`

## Error Handling

\`\`\`javascript
import { ApiError, ValidationError, RateLimitError } from '@example/api-client';

try {
await client.users.create({ email: 'invalid' });
} catch (error) {
if (error instanceof ValidationError) {
console.log(error.details); // Field-level errors
} else if (error instanceof RateLimitError) {
console.log(`Retry after ${error.retryAfter} seconds`);
} else if (error instanceof ApiError) {
console.log(error.code, error.message);
}
}
\`\`\`

## TypeScript Support

The SDK includes full TypeScript definitions:

\`\`\`typescript
import { ApiClient, User, CreateUserParams } from '@example/api-client';

const params: CreateUserParams = {
email: 'typed@example.com',
name: 'Typed User'
};

const user: User = await client.users.create(params);
\`\`\`