API Design Patterns

API Design Patterns

RESTful API design principles for building consistent, developer-friendly APIs. Contains 38 rules across 7 categories covering resource design, error handling, security, pagination, versioning, response format, and documentation.

Metadata

• Version: 2.0.0
• Rule Count: 38 rules across 7 categories
• License: MIT

When to Apply

Reference these guidelines when:

• Designing new API endpoints
• Reviewing existing API structure
• Implementing error handling and validation
• Setting up pagination, filtering, and sorting
• Planning API versioning strategy
• Configuring API security (auth, CORS, rate limiting)
• Writing API documentation (OpenAPI/Swagger)

Rule Categories by Priority

Quick Reference

1. Resource Design (CRITICAL)

• rest-nouns-not-verbs - Use nouns for endpoints, not verbs
• rest-plural-resources - Use plural resource names
• rest-http-methods - Correct HTTP method usage (GET, POST, PUT, PATCH, DELETE)
• rest-nested-resources - Proper resource nesting (max 2 levels)
• rest-status-codes - Appropriate HTTP status codes
• rest-idempotency - Idempotent operations with idempotency keys
• rest-hateoas - Hypermedia links for discoverability
• rest-resource-actions - Non-CRUD actions as sub-resources

2. Error Handling (CRITICAL)

• error-consistent-format - Consistent error response structure
• error-meaningful-messages - Helpful, actionable error messages
• error-validation-details - Field-level validation errors
• error-error-codes - Machine-readable error codes
• error-no-stack-traces - Never expose stack traces in production
• error-request-id - Include request IDs for debugging

3. Security (CRITICAL)

• sec-authentication - Proper auth implementation (OAuth2/JWT)
• sec-authorization - Resource-level permissions (RBAC)
• sec-rate-limiting - Prevent abuse with rate limiting
• sec-input-validation - Validate and sanitize all input
• sec-cors-config - CORS configuration with whitelists
• sec-https-only - Enforce HTTPS for all traffic
• sec-sensitive-data - Protect passwords, tokens, PII

4. Pagination & Filtering (HIGH)

• page-cursor-based - Cursor pagination for large datasets
• page-offset-based - Offset pagination for simple cases
• page-consistent-params - Consistent parameter naming
• page-metadata - Include pagination metadata in responses
• filter-query-params - Filter via query parameters
• sort-flexible - Flexible sorting with - prefix for descending

5. Versioning (HIGH)

• ver-url-path - Version in URL path (/api/v1/)
• ver-header-based - Version via Accept header
• ver-backward-compatible - Maintain backward compatibility
• ver-deprecation - Deprecation strategy with Sunset header

6. Response Format (MEDIUM)

• resp-consistent-structure - Consistent response envelope
• resp-json-conventions - JSON naming conventions
• resp-partial-responses - Field selection (sparse fieldsets)
• resp-compression - Response compression (gzip/Brotli)

7. Documentation (MEDIUM)

• doc-openapi - OpenAPI/Swagger specification
• doc-examples - Request/response examples
• doc-changelog - API changelog

Essential Guidelines

Resource Naming

# ❌ Verbs in URLs
GET    /getUsers
POST   /createUser

# ✅ Nouns with HTTP methods
GET    /users          # List users
POST   /users          # Create user
GET    /users/123      # Get user
PUT    /users/123      # Update user (full)
PATCH  /users/123      # Update user (partial)
DELETE /users/123      # Delete user

Error Response Format

{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "The request contains invalid data",
    "details": [
      {
        "field": "email",
        "code": "INVALID_FORMAT",
        "message": "Please provide a valid email address"
      }
    ],
    "request_id": "req_abc123"
  }
}

Pagination

{
  "data": [...],
  "meta": {
    "current_page": 2,
    "per_page": 20,
    "total_pages": 10,
    "total_count": 195
  },
  "links": {
    "first": "/users?page=1&per_page=20",
    "prev": "/users?page=1&per_page=20",
    "next": "/users?page=3&per_page=20",
    "last": "/users?page=10&per_page=20"
  }
}

Rate Limiting Headers

HTTP/1.1 200 OK
X-RateLimit-Limit: 1000
X-RateLimit-Remaining: 998
X-RateLimit-Reset: 1640995200

How to Use

Read individual rule files for detailed explanations:

rules/rest-http-methods.md
rules/error-consistent-format.md
rules/page-cursor-based.md
rules/sec-authentication.md
rules/ver-url-path.md
rules/doc-openapi.md

References

• RESTful API Guidelines
• Zalando RESTful API Guidelines
• Microsoft API Guidelines
• Google API Design Guide
• OpenAPI Specification

Full Compiled Document

For the complete guide with all rules expanded: AGENTS.md