api-design-patterns

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安装

npx skills add https://github.com/bobmatnyc/claude-mpm-skills --skill api-design-patterns

API Design Patterns

Design robust, scalable APIs using proven patterns for REST, GraphQL, and gRPC with proper versioning, authentication, and error handling.

Quick Reference

API Style Selection:

REST: Resource-based CRUD, simple clients, HTTP-native caching GraphQL: Client-driven queries, complex data graphs, real-time subscriptions gRPC: High-performance RPC, microservices, strong typing, streaming

Critical Patterns:

Versioning: URI (/v1/users), header (Accept: application/vnd.api+json;version=1), content negotiation Pagination: Offset (simple), cursor (stable), keyset (performant) Auth: OAuth2 (delegated), JWT (stateless), API keys (service-to-service) Rate limiting: Token bucket, fixed window, sliding window Idempotency: Idempotency keys, conditional requests, safe retry

See references/ for deep dives: rest-patterns.md, graphql-patterns.md, grpc-patterns.md, versioning-strategies.md, authentication.md

Core Principles Universal API Design Standards

Apply these principles across all API styles:

  1. Consistency Over Cleverness

Follow established conventions for your API style Use predictable naming patterns (snake_case or camelCase, pick one) Maintain consistent error response formats Version breaking changes, never surprise clients

  1. Design for Evolution

Plan for versioning from day one Use optional fields with sensible defaults Deprecate gracefully with sunset dates Document breaking vs non-breaking changes

  1. Security by Default

Require authentication unless explicitly public Use HTTPS/TLS for all production endpoints Implement rate limiting and throttling Validate and sanitize all inputs Return minimal error details to clients

  1. Developer Experience First

Provide comprehensive documentation (OpenAPI, GraphQL schema) Return meaningful error messages with actionable guidance Use standard HTTP status codes correctly Include request IDs for debugging Offer SDKs and code generators API Style Decision Tree When to Choose REST

✅ Use REST when:

Building CRUD-focused resource APIs Clients need HTTP caching (ETags, Cache-Control) Wide platform compatibility required (browsers, mobile, IoT) Simple, stateless client-server model fits Team familiar with HTTP/REST conventions

❌ Avoid REST when:

Complex data fetching with nested relationships (N+1 queries) Real-time updates are primary use case Need strong typing and code generation High-performance RPC between microservices

Example Use Cases: Public APIs, mobile backends, traditional web services

When to Choose GraphQL

✅ Use GraphQL when:

Clients need flexible, client-driven queries Complex data graphs with nested relationships Multiple client types with different data needs Real-time subscriptions required Strong typing and schema validation needed

❌ Avoid GraphQL when:

Simple CRUD operations dominate HTTP caching is critical (GraphQL uses POST) File uploads are primary feature (requires extensions) Team lacks GraphQL expertise Performance optimization is complex (N+1 problem)

Example Use Cases: Client-facing APIs, dashboards, mobile apps with varied UIs

When to Choose gRPC

✅ Use gRPC when:

Microservice-to-microservice communication High performance and low latency critical Bidirectional streaming needed Strong typing with Protocol Buffers Polyglot environments (language interop)

❌ Avoid gRPC when:

Browser clients (limited support, needs grpc-web) HTTP/JSON required for compatibility Human-readable payloads preferred Simple request/response patterns

Example Use Cases: Internal microservices, streaming data, service mesh

REST API Patterns Resource Naming

✅ Good: Plural nouns, hierarchical

GET /users # List users GET /users/123 # Get user POST /users # Create user PUT /users/123 # Update user (full) PATCH /users/123 # Update user (partial) DELETE /users/123 # Delete user GET /users/123/orders # User's orders (sub-resource)

❌ Bad: Verbs, mixed conventions

GET /getUsers # Don't use verbs POST /user/create # Don't use verbs GET /Users/123 # Don't capitalize GET /user/123 # Don't mix singular/plural

HTTP Status Codes

Success Codes:

200 OK: Successful GET, PUT, PATCH, DELETE with body 201 Created: Successful POST, return Location header 202 Accepted: Async operation started 204 No Content: Successful DELETE, no body

Client Error Codes:

400 Bad Request: Invalid input, validation error 401 Unauthorized: Missing or invalid authentication 403 Forbidden: Authenticated but insufficient permissions 404 Not Found: Resource doesn't exist 409 Conflict: State conflict (duplicate, version mismatch) 422 Unprocessable Entity: Semantic validation error 429 Too Many Requests: Rate limit exceeded

Server Error Codes:

500 Internal Server Error: Unexpected error 502 Bad Gateway: Upstream service error 503 Service Unavailable: Temporary outage 504 Gateway Timeout: Upstream timeout Error Response Format

✅ Consistent error structure

{ "error": { "code": "VALIDATION_ERROR", "message": "Invalid request parameters", "details": [ { "field": "email", "message": "Invalid email format", "code": "INVALID_FORMAT" } ], "request_id": "req_abc123", "documentation_url": "https://api.example.com/docs/errors/validation" } }

Pagination Patterns

Offset Pagination (simple, familiar):

GET /users?limit=20&offset=40

✅ Use for: Small datasets, admin interfaces ❌ Avoid for: Large datasets (skips become expensive), real-time data

Cursor Pagination (stable, efficient):

GET /users?limit=20&cursor=eyJpZCI6MTIzfQ Response: { "data": [...], "next_cursor": "eyJpZCI6MTQzfQ" }

✅ Use for: Infinite scroll, real-time feeds, large datasets ❌ Avoid for: Random access, page numbers

Keyset Pagination (performant):

GET /users?limit=20&after_id=123

✅ Use for: Ordered data, database index friendly ❌ Avoid for: Complex sorting, multiple sort keys

See references/rest-patterns.md for filtering, sorting, field selection, HATEOAS

GraphQL Patterns Schema Design

✅ Good: Clear types, nullable by default

type User { id: ID! # Non-null ID email: String! # Required field name: String # Optional (nullable by default) createdAt: DateTime! orders: [Order!]! # Non-null array of non-null orders }

type Query { user(id: ID!): User users(first: Int, after: String): UserConnection! }

type Mutation { createUser(input: CreateUserInput!): CreateUserPayload! }

input CreateUserInput { email: String! name: String }

type CreateUserPayload { user: User userEdge: UserEdge errors: [UserError!] }

Resolver Patterns

Avoid N+1 Queries with DataLoader:

import DataLoader from 'dataloader';

const userLoader = new DataLoader(async (userIds: string[]) => { const users = await db.users.findMany({ where: { id: { in: userIds } } }); return userIds.map(id => users.find(u => u.id === id)); });

// Resolver batches queries automatically const resolvers = { Order: { user: (order) => userLoader.load(order.userId) } };

Query Complexity Analysis

Prevent expensive queries:

import { createComplexityLimitRule } from 'graphql-validation-complexity';

const server = new ApolloServer({ schema, validationRules: [ createComplexityLimitRule(1000, { onCost: (cost) => console.log('Query cost:', cost), }), ], });

See references/graphql-patterns.md for subscriptions, relay cursor connections, error handling

gRPC Patterns Service Definition syntax = "proto3";

package users.v1;

service UserService { rpc GetUser (GetUserRequest) returns (User) {} rpc ListUsers (ListUsersRequest) returns (ListUsersResponse) {} rpc CreateUser (CreateUserRequest) returns (User) {} rpc StreamUsers (StreamUsersRequest) returns (stream User) {} rpc BidiChat (stream ChatMessage) returns (stream ChatMessage) {} }

message User { string id = 1; string email = 2; string name = 3; google.protobuf.Timestamp created_at = 4; }

message GetUserRequest { string id = 1; }

message ListUsersRequest { int32 page_size = 1; string page_token = 2; }

message ListUsersResponse { repeated User users = 1; string next_page_token = 2; }

Error Handling import ( "google.golang.org/grpc/codes" "google.golang.org/grpc/status" )

func (s server) GetUser(ctx context.Context, req pb.GetUserRequest) (*pb.User, error) { if req.Id == "" { return nil, status.Error(codes.InvalidArgument, "user ID is required") }

user, err := s.db.GetUser(ctx, req.Id)
if err != nil {
    if errors.Is(err, sql.ErrNoRows) {
        return nil, status.Error(codes.NotFound, "user not found")
    }
    return nil, status.Error(codes.Internal, "database error")
}

return user, nil

}

See references/grpc-patterns.md for streaming, interceptors, metadata, health checks

Versioning Strategies URI Versioning (Simple, Explicit)

✅ Most common, easy to understand

GET /v1/users/123 GET /v2/users/123

Pros: Clear, easy to route, browser-friendly Cons: Couples version to URL, duplicates routes

Header Versioning (Clean URLs) GET /users/123 Accept: application/vnd.myapi.v2+json

Pros: Clean URLs, version separate from resource Cons: Less visible, harder to test manually

Content Negotiation (Granular) GET /users/123 Accept: application/vnd.myapi.user.v2+json

Pros: Resource-level versioning, backward compatible Cons: Complex, harder to implement

Version Deprecation Process { "version": "1.0", "deprecated": true, "sunset_date": "2025-12-31", "migration_guide": "https://docs.api.com/v1-to-v2", "replacement_version": "2.0" }

Include deprecation warnings:

HTTP/1.1 200 OK Deprecation: true Sunset: Sat, 31 Dec 2025 23:59:59 GMT Link: https://docs.api.com/v1-to-v2; rel="deprecation"

See references/versioning-strategies.md for detailed migration patterns

Authentication & Authorization OAuth 2.0 (Delegated Access)

Use for: Third-party access, user consent, token refresh

Authorization Code Flow (most secure for web/mobile):

  1. Client redirects to /authorize
  2. User authenticates, grants permissions
  3. Auth server redirects to callback with code
  4. Client exchanges code for access token
  5. Client uses access token for API requests

Request token

POST /oauth/token Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code &code=AUTH_CODE &redirect_uri=https://client.com/callback &client_id=CLIENT_ID &client_secret=CLIENT_SECRET

Response

{ "access_token": "eyJhbGc...", "token_type": "Bearer", "expires_in": 3600, "refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA", "scope": "read write" }

Use token

GET /v1/users/me Authorization: Bearer eyJhbGc...

JWT (Stateless Auth)

Use for: Microservices, stateless API auth, short-lived tokens

✅ Good: Minimal claims, short expiry

{ "sub": "user_123", "iat": 1516239022, "exp": 1516242622, "scope": "read:users write:orders" }

Validation:

import jwt from 'jsonwebtoken';

const token = req.headers.authorization?.split(' ')[1]; const payload = jwt.verify(token, process.env.JWT_SECRET); req.userId = payload.sub;

API Keys (Service-to-Service)

Use for: Server-to-server, CLI tools, webhooks

GET /v1/users X-API-Key: sk_live_abc123...

Or query parameter (less secure)

GET /v1/users?api_key=sk_live_abc123

Key Practices:

Prefix keys with environment (sk_live_, sk_test_) Hash keys before storage (bcrypt, scrypt) Allow key rotation without downtime Support multiple keys per user Rate limit per key

See references/authentication.md for API key rotation, scopes, RBAC

Rate Limiting Token Bucket (Burst-Friendly) Bucket: 100 tokens, refill 10/second Request costs 1 token Allows bursts up to bucket size

Headers:

HTTP/1.1 200 OK X-RateLimit-Limit: 100 X-RateLimit-Remaining: 73 X-RateLimit-Reset: 1640995200

429 Response:

HTTP/1.1 429 Too Many Requests Retry-After: 60 X-RateLimit-Limit: 100 X-RateLimit-Remaining: 0 X-RateLimit-Reset: 1640995200

{ "error": { "code": "RATE_LIMIT_EXCEEDED", "message": "Rate limit exceeded. Try again in 60 seconds.", "limit": 100, "reset_at": "2025-01-01T00:00:00Z" } }

Sliding Window (Fair Distribution)

Counts requests in rolling time window. More accurate than fixed window.

Per-User vs Per-IP Per-User: Authenticated requests, fair quotas Per-IP: Unauthenticated requests, prevent abuse Combined: Both limits, take stricter Idempotency Idempotent Methods (HTTP Spec)

Naturally Idempotent: GET, PUT, DELETE, HEAD, OPTIONS Not Idempotent: POST, PATCH

Idempotency Keys

Make POST requests idempotent:

POST /v1/payments Idempotency-Key: uuid-or-client-generated-key Content-Type: application/json

{ "amount": 1000, "currency": "USD", "customer": "cust_123" }

Server behavior:

First request: Process and store result with key Duplicate request (same key): Return stored result (200 or 201) Different request (same key): Return 409 Conflict

Implementation:

const idempotencyKey = req.headers['idempotency-key']; if (idempotencyKey) { const cached = await redis.get(idempotency:${idempotencyKey}); if (cached) { return res.status(cached.status).json(cached.body); } }

const result = await processPayment(req.body); await redis.setex(idempotency:${idempotencyKey}, 86400, { status: 201, body: result });

Conditional Requests

Use ETags for safe updates:

Get resource with ETag

GET /v1/users/123 Response: ETag: "abc123"

Update only if unchanged

PUT /v1/users/123 If-Match: "abc123"

412 Precondition Failed if ETag changed

Caching Strategies HTTP Caching Headers

Public, cacheable for 1 hour

Cache-Control: public, max-age=3600

Private (user-specific), revalidate

Cache-Control: private, must-revalidate, max-age=0

No caching

Cache-Control: no-store, no-cache, must-revalidate

ETag Validation

Server returns ETag

GET /v1/users/123 Response: ETag: "33a64df551425fcc55e4d42a148795d9f25f89d4" Cache-Control: max-age=3600

Client conditional request

GET /v1/users/123 If-None-Match: "33a64df551425fcc55e4d42a148795d9f25f89d4"

304 Not Modified if unchanged (saves bandwidth)

HTTP/1.1 304 Not Modified

Last-Modified GET /v1/users/123 Response: Last-Modified: Wed, 21 Oct 2025 07:28:00 GMT

Conditional request

GET /v1/users/123 If-Modified-Since: Wed, 21 Oct 2025 07:28:00 GMT

304 Not Modified if not modified

Webhooks Event Delivery POST https://client.com/webhooks/payments Content-Type: application/json X-Webhook-Signature: sha256=abc123... X-Webhook-Id: evt_abc123 X-Webhook-Timestamp: 1640995200

{ "id": "evt_abc123", "type": "payment.succeeded", "created": 1640995200, "data": { "object": { "id": "pay_123", "amount": 1000, "status": "succeeded" } } }

Signature Verification import crypto from 'crypto';

function verifyWebhookSignature( payload: string, signature: string, secret: string ): boolean { const expectedSignature = crypto .createHmac('sha256', secret) .update(payload) .digest('hex'); return crypto.timingSafeEqual( Buffer.from(signature), Buffer.from(sha256=${expectedSignature}) ); }

Retry Strategy Exponential backoff: 1s, 2s, 4s, 8s, 16s, 32s, 64s Timeout: 5-30 seconds per attempt Max attempts: 3-7 attempts Dead letter queue: Store failed events Manual retry: UI for re-sending failed events API Documentation OpenAPI/Swagger (REST) openapi: 3.0.0 info: title: User API version: 1.0.0 paths: /users/{id}: get: summary: Get user by ID parameters: - name: id in: path required: true schema: type: string responses: '200': description: Successful response content: application/json: schema: $ref: '#/components/schemas/User' '404': description: User not found components: schemas: User: type: object required: [id, email] properties: id: type: string email: type: string format: email name: type: string

GraphQL Schema (Self-Documenting)

GraphQL introspection provides automatic documentation. Use descriptions:

""" Represents a user account in the system. Created via the createUser mutation. """ type User { """Unique identifier for the user""" id: ID!

"""Email address, must be unique""" email: String!

"""Optional display name""" name: String }

API Documentation Best Practices Interactive examples: Provide working code samples Authentication guide: Step-by-step auth setup Error catalog: Document all error codes with examples Rate limits: Clearly state limits and headers Changelog: Track breaking and non-breaking changes Migration guides: Version upgrade instructions SDKs: Provide client libraries for popular languages Anti-Patterns

❌ Over-fetching (REST): Returning entire objects when fields are unused ✅ Solution: Support field selection (?fields=id,name,email)

❌ Under-fetching (REST): Requiring multiple requests for related data ✅ Solution: Support expansion (?expand=orders,profile) or use GraphQL

❌ Chatty APIs: Too many round-trips for common operations ✅ Solution: Batch endpoints, compound documents, or GraphQL

❌ Ignoring HTTP semantics: Using GET for mutations, wrong status codes ✅ Solution: Follow HTTP spec, use correct methods and status codes

❌ Exposing internal structure: URLs/schemas mirror database ✅ Solution: Design resource-oriented APIs independent of storage

❌ Missing versioning: Breaking changes without version increments ✅ Solution: Version from day one, never break existing versions

❌ Poor error messages: Generic "An error occurred" ✅ Solution: Specific, actionable error messages with codes

❌ No rate limiting: APIs vulnerable to abuse ✅ Solution: Implement rate limiting from the start

Testing Strategies Contract Testing // Pact contract test import { PactV3 } from '@pact-foundation/pact';

const provider = new PactV3({ consumer: 'FrontendApp', provider: 'UserAPI' });

it('gets a user by ID', () => { provider .given('user 123 exists') .uponReceiving('a request for user 123') .withRequest({ method: 'GET', path: '/users/123' }) .willRespondWith({ status: 200, body: { id: '123', email: 'user@example.com' } }); });

Load Testing // k6 load test import http from 'k6/http'; import { check } from 'k6';

export const options = { stages: [ { duration: '30s', target: 20 }, { duration: '1m', target: 20 }, { duration: '10s', target: 0 } ], thresholds: { http_req_duration: ['p(95)<500'], // 95% under 500ms http_req_failed: ['rate<0.01'] // <1% errors } };

export default function () { const res = http.get('https://api.example.com/users'); check(res, { 'status is 200': (r) => r.status === 200, 'response time < 500ms': (r) => r.timings.duration < 500 }); }

Related Skills graphql: Deep GraphQL schema design, resolvers, Apollo Server typescript: Type-safe API clients and servers nodejs-backend: Express/Fastify REST API implementation django: Django REST Framework patterns fastapi: FastAPI Python REST/GraphQL APIs flask: Flask-RESTful patterns References rest-patterns.md: Deep REST coverage (HATEOAS, filtering, field selection) graphql-patterns.md: GraphQL subscriptions, relay cursor connections, federation grpc-patterns.md: Streaming patterns, interceptors, service mesh integration versioning-strategies.md: Detailed versioning approaches and migration patterns authentication.md: OAuth flows, JWT best practices, API key rotation, RBAC Additional Resources REST API Design Rulebook - O'Reilly REST guide GraphQL Best Practices - Official GraphQL guide gRPC Best Practices - Official gRPC guide RFC 7807: Problem Details for HTTP APIs - Standard error format OpenAPI Specification - REST documentation standard

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