API Design

API Design Best Practices

REST Fundamentals

Resource Naming

# Good - nouns, plural, lowercase
GET    /users
GET    /users/{id}
POST   /users
PUT    /users/{id}
DELETE /users/{id}

# Nested resources
GET    /users/{id}/orders
POST   /users/{id}/orders

# Bad
GET    /getUsers
POST   /createUser
GET    /user_list

HTTP Methods

Status Codes

# Success
200 OK              - Successful GET, PUT, PATCH
201 Created         - Successful POST
204 No Content      - Successful DELETE

# Client Errors
400 Bad Request     - Invalid input
401 Unauthorized    - Authentication required
403 Forbidden       - Authenticated but not allowed
404 Not Found       - Resource doesn't exist
409 Conflict        - Resource state conflict
422 Unprocessable   - Validation failed

# Server Errors
500 Internal Error  - Unexpected server error
502 Bad Gateway     - Upstream service error
503 Unavailable     - Service temporarily unavailable

Request/Response Design

Request Format

POST /users
Content-Type: application/json

{
  "name": "Alice",
  "email": "alice@example.com",
  "role": "admin"
}

Response Format

{
  "data": {
    "id": "user_123",
    "name": "Alice",
    "email": "alice@example.com",
    "role": "admin",
    "createdAt": "2024-01-15T10:30:00Z"
  }
}

Error Response

{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Invalid input data",
    "details": [
      {
        "field": "email",
        "message": "Invalid email format"
      }
    ]
  }
}

Pagination

Offset-based

GET /users?offset=20&limit=10

{
  "data": [...],
  "pagination": {
    "total": 100,
    "offset": 20,
    "limit": 10
  }
}

Cursor-based (Preferred)

GET /users?cursor=abc123&limit=10

{
  "data": [...],
  "pagination": {
    "nextCursor": "xyz789",
    "hasMore": true
  }
}

Filtering and Sorting

Query Parameters

# Filtering
GET /users?status=active&role=admin

# Sorting
GET /users?sort=createdAt:desc

# Multiple sorts
GET /users?sort=role:asc,name:asc

# Field selection
GET /users?fields=id,name,email

Search

GET /users?q=alice
GET /products?search=laptop&category=electronics

Versioning

URL Path (Recommended)

/v1/users
/v2/users

Header

GET /users
Accept: application/vnd.api+json; version=1

Query Parameter

GET /users?version=1

Authentication

Bearer Token

Authorization: Bearer eyJhbGciOiJIUzI1NiIs...

API Key

X-API-Key: your-api-key
# Or in query (less secure)
?api_key=your-api-key

Rate Limiting

Response Headers

X-RateLimit-Limit: 100
X-RateLimit-Remaining: 95
X-RateLimit-Reset: 1640000000

429 Response

{
  "error": {
    "code": "RATE_LIMITED",
    "message": "Too many requests",
    "retryAfter": 60
  }
}

GraphQL Patterns

Schema Design

type User {
  id: ID!
  name: String!
  email: String!
  orders(first: Int, after: String): OrderConnection!
}

type Order {
  id: ID!
  total: Float!
  status: OrderStatus!
  user: User!
}

enum OrderStatus {
  PENDING
  PROCESSING
  SHIPPED
  DELIVERED
}

Queries

query GetUser($id: ID!) {
  user(id: $id) {
    id
    name
    orders(first: 10) {
      edges {
        node {
          id
          total
        }
      }
    }
  }
}

Mutations

mutation CreateUser($input: CreateUserInput!) {
  createUser(input: $input) {
    user {
      id
      name
    }
    errors {
      field
      message
    }
  }
}

Documentation

OpenAPI/Swagger

openapi: 3.0.0
info:
  title: User API
  version: 1.0.0

paths:
  /users:
    get:
      summary: List users
      parameters:
        - name: limit
          in: query
          schema:
            type: integer
            default: 20
      responses:
        '200':
          description: Success
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/UserList'

HATEOAS

Links in Response

{
  "data": {
    "id": "user_123",
    "name": "Alice"
  },
  "links": {
    "self": "/users/user_123",
    "orders": "/users/user_123/orders",
    "profile": "/users/user_123/profile"
  }
}

Best Practices

Consistency

• Use consistent naming (camelCase or snake_case)
• Consistent error format across all endpoints
• Consistent pagination format

Security

• Always use HTTPS
• Validate all input
• Don't expose internal IDs
• Rate limit all endpoints
• Use appropriate authentication

Performance

• Support compression (gzip)
• Cache with ETags
• Allow field selection
• Implement pagination

Anti-Patterns to Avoid

• Verbs in URLs (/getUser)
• Returning 200 for errors
• Inconsistent response formats
• Missing pagination
• Exposing database IDs
• No versioning strategy
• Missing rate limiting
• Chatty APIs (many small calls)