api-designer

name api-designer description Design and document RESTful and GraphQL APIs with OpenAPI/Swagger specifications, authentication patterns, versioning strategies, and best practices. Use for: (1) Creating API specifications, (2) Designing REST endpoints, (3) GraphQL schema design, (4) API authentication and authorization, (5) API versioning strategies, (6) Documentation generation API Designer Overview This skill provides comprehensive guidance for designing, documenting, and implementing modern APIs. It covers both REST and GraphQL paradigms, with emphasis on industry best practices, clear documentation, and maintainable architecture. Use this skill to create production-ready API designs that are scalable, secure, and developer-friendly. Core Capabilities REST API Design Resource-oriented endpoint design with proper URL structure HTTP method semantics and status code usage Request/response payload design with consistent naming Pagination, filtering, and sorting strategies Error handling and validation patterns GraphQL API Design Schema definition with type system and relationships Query and mutation design with proper input types Resolver patterns and performance optimization Fragment usage and directive implementation N+1 problem prevention strategies API Documentation OpenAPI 3.0 specification generation Interactive documentation with Swagger UI Authentication and authorization documentation Example requests/responses with multiple scenarios Code generation from specifications Authentication & Authorization OAuth 2.0 flows (authorization code, client credentials, PKCE) JWT token design, validation, and rotation API key management and rotation strategies Role-based access control (RBAC) implementation Rate limiting and throttling patterns API Versioning URL versioning and header-based versioning strategies Semantic versioning for API releases Deprecation planning and communication Backward compatibility maintenance Migration path design When to Use This Skill Use this skill when: Designing a new API from scratch or refactoring existing endpoints Creating OpenAPI/Swagger specifications for documentation Implementing authentication and authorization flows Planning API versioning and deprecation strategies Designing GraphQL schemas and resolvers Establishing API governance and best practices REST API Design Workflow Step 1: Identify Resources Identify core resources (nouns) your API will expose: Resources: Users, Posts, Comments Collections: - GET /users (List all users) - POST /users (Create new user) Individual Resources: - GET /users/{id} (Get specific user) - PUT /users/{id} (Replace user - full update) - PATCH /users/{id} (Update user - partial) - DELETE /users/{id} (Delete user) Nested Resources: - GET /users/{id}/posts (Get user's posts) - POST /users/{id}/posts (Create post for user) Step 2: Design URL Structure Follow RESTful naming conventions: Best Practices : Use plural nouns: /users , /posts (not /user , /post ) Use hyphens for multi-word: /blog-posts (not /blogPosts or /blog_posts ) Keep URLs lowercase Limit nesting to 2 levels maximum Use query parameters for filtering: /posts?status=published&author=123 Quick Examples : ✅ Good: GET /users GET /users/123/posts GET /posts?published=true&limit=10 ❌ Bad: GET /getUsers GET /users/123/posts/comments/likes (too deep nesting) GET /posts/published (use query param instead) Step 3: Choose HTTP Methods Map operations to standard HTTP methods: GET : Retrieve resource(s) - Safe, idempotent, cacheable POST : Create new resource - Returns 201 Created with Location header PUT : Replace entire resource - Idempotent, full replacement PATCH : Partial update - Update specific fields only DELETE : Remove resource - Idempotent, returns 204 or 200 Step 4: Design Request/Response Payloads Structure JSON payloads consistently: Naming Conventions : Use camelCase for JSON field names Use ISO 8601 for timestamps (UTC) Use consistent ID formats with prefixes: usr_ , post_ Include metadata: createdAt , updatedAt Example Response : { "id" : "usr_1234567890" , "username" : "johndoe" , "email" : "john@example.com" , "profile" : { "firstName" : "John" , "lastName" : "Doe" } , "createdAt" : "2025-10-25T10:30:00Z" , "updatedAt" : "2025-10-25T10:30:00Z" } Step 5: Implement Error Handling Design comprehensive error responses: Error Response Format : { "error" : { "code" : "VALIDATION_ERROR" , "message" : "Invalid request parameters" , "details" : [ { "field" : "email" , "message" : "Email format is invalid" } ] , "requestId" : "req_abc123xyz" , "timestamp" : "2025-10-25T10:30:00Z" } } Key Status Codes : 200 OK : Successful GET, PUT, PATCH 201 Created : Successful POST 204 No Content : Successful DELETE 400 Bad Request : Invalid request data 401 Unauthorized : Missing/invalid authentication 403 Forbidden : Authenticated but not authorized 404 Not Found : Resource doesn't exist 422 Unprocessable Entity : Validation errors 429 Too Many Requests : Rate limit exceeded 500 Internal Server Error : Server error Step 6: Add Pagination and Filtering Cursor-Based Pagination (recommended for large datasets): GET /posts?limit=20&cursor=eyJpZCI6MTIzfQ Response: { "data": [...], "pagination": { "nextCursor": "eyJpZCI6MTQzfQ", "hasMore": true } } Offset-Based Pagination (simpler for small datasets): GET /posts?limit=20&offset=40&sort=-createdAt Response: { "data": [...], "pagination": { "total": 500, "limit": 20, "offset": 40 } } For detailed pagination strategies and filtering patterns, see references/rest_best_practices.md . GraphQL API Design Workflow Step 1: Define Schema Types Create type definitions for your domain: type User { id : ID ! username : String ! email : String ! profile : Profile posts ( limit : Int = 10 ) : [ Post ! ] ! createdAt : DateTime ! } type Post { id : ID ! title : String ! content : String ! published : Boolean ! author : User ! tags : [ String ! ] ! createdAt : DateTime ! } Step 2: Design Queries Define read operations with filtering: type Query { user ( id : ID ! ) : User post ( id : ID ! ) : Post users ( limit : Int = 10 offset : Int = 0 search : String ) : UserConnection ! posts ( limit : Int = 10 published : Boolean authorId : ID tags : [ String ! ] ) : PostConnection ! } Step 3: Design Mutations Define write operations with input types and error handling: type Mutation { createUser ( input : CreateUserInput ! ) : CreateUserPayload ! updateUser ( id : ID ! , input : UpdateUserInput ! ) : UpdateUserPayload ! createPost ( input : CreatePostInput ! ) : CreatePostPayload ! } input CreateUserInput { username : String ! email : String ! password : String ! } type CreateUserPayload { user : User errors : [ Error ! ] } For complete GraphQL schema examples, see examples/graphql_schema.graphql . Authentication Patterns OAuth 2.0 Quick Reference Authorization Code Flow (web apps with backend): 1. Redirect to /oauth/authorize with client_id, redirect_uri, scope 2. User authenticates and grants permission 3. Receive authorization code via redirect 4. Exchange code for access token at /oauth/token 5. Use access token in Authorization header Client Credentials Flow (service-to-service): POST /oauth/token { "grant_type": "client_credentials", "client_id": "CLIENT_ID", "client_secret": "SECRET" } PKCE Flow (mobile/SPA - most secure for public clients): 1. Generate code_verifier and code_challenge 2. Request authorization with code_challenge 3. Exchange code for token with code_verifier (no client_secret needed) JWT Token Design Token Structure : { "header" : { "alg" : "RS256" , "typ" : "JWT" } , "payload" : { "sub" : "usr_1234567890" , "iat" : 1698336000 , "exp" : 1698339600 , "scope" : [ "read:posts" , "write:posts" ] , "roles" : [ "user" , "editor" ] } } Usage : Authorization: Bearer eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9... API Key Authentication X-API-Key: sk_live_abcdef1234567890 Best Practices : Different keys for different environments (dev, staging, prod) Support multiple keys per account for rotation Implement key expiration and usage logging Never expose keys in client-side code For comprehensive authentication patterns including refresh tokens, MFA, and security best practices, see references/authentication.md . API Versioning Strategies URL Versioning (Recommended) /v1/users /v2/users Pros : Clear, explicit, easy to cache and route Cons : URL proliferation, multiple codebases Header Versioning Accept: application/vnd.myapi.v2+json API-Version: 2 Pros : Clean URLs, same endpoint Cons : Less visible, harder to test in browser When to Version Create new version for : Removing endpoints or fields Changing field types or names Modifying authentication methods Breaking existing client contracts Don't version for : Adding new optional fields Adding new endpoints Bug fixes or performance improvements For detailed versioning strategies, deprecation processes, and migration patterns, see references/versioning-strategies.md . OpenAPI Specification Basic Structure openapi: 3.0 .0 info: title: My API version: 1.0 .0 description: API description servers: - url: https://api.example.com/v1 paths: /users: get: summary: List users parameters: - name: limit in: query schema: type: integer default: 10 responses: '200': description: Successful response content: application/json: schema: $ref: '#/components/schemas/UserList' components: schemas: User: type: object required: - username - email properties: id: type: string username: type: string email: type: string format: email For complete OpenAPI specification examples, see examples/openapi_spec.yaml . Generating Documentation Use the helper script to generate and validate specs: # Generate OpenAPI spec from code python scripts/api_helper.py generate --input api.py --output openapi.yaml # Validate existing spec python scripts/api_helper.py validate --spec openapi.yaml # Generate documentation site python scripts/api_helper.py docs --spec openapi.yaml --output docs/ Best Practices Summary Consistency Use consistent naming conventions across all endpoints Standardize error response format Apply same authentication pattern everywhere Use uniform timestamp format (ISO 8601 with UTC) Security Always use HTTPS in production Validate all input data thoroughly Implement rate limiting per user/key/IP Use proper authentication for all endpoints Never expose sensitive data in URLs or logs Implement proper CORS configuration Performance Use pagination for large datasets Implement caching headers (ETag, Cache-Control) Support compression (gzip) Use cursor-based pagination for real-time data Implement field selection for sparse fieldsets Documentation Document all endpoints with OpenAPI Provide example requests and responses Document error codes and meanings Include authentication instructions Keep documentation in sync with code Maintainability Version APIs appropriately with clear deprecation timelines Provide deprecation warnings before removing features Write integration tests for all endpoints Monitor API usage, errors, and performance Maintain backward compatibility when possible Common Patterns Health Check GET /health Response: { "status": "ok", "timestamp": "2025-10-25T10:30:00Z" } Batch Operations POST /users/batch { "operations": [ { "method": "POST", "path": "/users", "body": {...} }, { "method": "PATCH", "path": "/users/123", "body": {...} } ] } Webhooks POST /webhooks/configure { "url": "https://your-app.com/webhook", "events": ["user.created", "post.published"], "secret": "webhook_secret_key" } For additional patterns including idempotency, long-running operations, file uploads, and soft deletes, see references/common-patterns.md . Quick Reference Checklists REST Endpoint Design Use plural nouns for collections Limit URL nesting to 2 levels Use appropriate HTTP methods Return correct status codes Implement consistent error format Add pagination for collections Include filtering and sorting Document with OpenAPI Implement authentication Add rate limiting GraphQL Schema Design Define clear type hierarchy Use nullable types appropriately Implement pagination (connections)