API Design

API Design Patterns

Guidelines for designing REST APIs.

Resource-Oriented Design

Design around resources, not actions.

Good

• GET /users/123 — Get a user
• POST /users — Create a user
• PUT /users/123 — Update a user
• DELETE /users/123 — Delete a user

Avoid

• GET /getUser — Action-oriented
• POST /createNewUser — Redundant with HTTP method

HTTP Methods

Status Codes

2xx Success

• 200 OK — Request succeeded
• 201 Created — Resource created (include Location header)
• 204 No Content — Success, no response body

4xx Client Error

• 400 Bad Request — Invalid input
• 401 Unauthorized — Authentication required
• 403 Forbidden — Authenticated, not allowed
• 404 Not Found — Resource doesn't exist
• 422 Unprocessable Entity — Valid format, semantic error

5xx Server Error

• 500 Internal Server Error — Unexpected error
• 503 Service Unavailable — Temporarily down

Error Responses

Consistent error format:

{
  "error": {
    "code": "INVALID_INPUT",
    "message": "User email is required",
    "details": {
      "field": "email"
    }
  }
}

Request/Response Bodies

JSON Structure

• Use camelCase for fields
• Flat structure (max 2-3 nesting levels)
• Avoid redundant wrappers

{
  "userId": 123,
  "name": "Alice",
  "email": "alice@example.com",
  "createdAt": "2026-01-15T10:30:00Z"
}

Timestamps

• Use ISO 8601: 2026-01-15T10:30:00Z
• Timezone-aware (UTC)

Pagination

GET /users?page=1&limit=20

Response:

{
  "data": [{...}, {...}],
  "pagination": {
    "page": 1,
    "limit": 20,
    "total": 150,
    "hasMore": true
  }
}

Filtering, Sorting

Filtering

GET /users?role=admin&status=active

Sorting

GET /posts?sort=createdAt:desc,title:asc

Versioning

URL Path (Recommended)

GET /v1/users
GET /v2/users

Header

Accept: application/vnd.myapi.v1+json

Announce 12 months before deprecating old versions.

Authentication

Bearer Token

Authorization: Bearer <token>

API Key

X-API-Key: your-key-here

Rate Limiting

Include in response headers:

X-RateLimit-Limit: 1000
X-RateLimit-Remaining: 500
X-RateLimit-Reset: 1234567890

Common Patterns

Nested Resources

GET /organizations/org1/teams/team1/members

Or flatten with query params:

GET /members?organizationId=org1&teamId=team1

Batch Operations

POST /users/batch
{
  "operations": [
    {"op": "create", "data": {...}},
    {"op": "update", "id": "123", "data": {...}}
  ]
}