backend-patternslisted

# Backend Development Patterns Backend architecture patterns and best practices for scalable server-side applications. > **Reuse-first** (per `~/.claude/rules-library/common/reuse-first.md`): > Before creating a new service / repository / middleware / > handler helper / validator / DTO, sweep the project's `lib/`, > `services/`, `repositories/`, `middleware/`, `validators/`, > `dto/` (or language-equivalent) directories. One source of > truth per concept (one auth middleware, one error envelope, one > pagination helper, one rate limiter, one DB client factory). > Extend with a parameter — never fork. ## When to Activate - Designing REST or GraphQL API endpoints - Implementing repository, service, or controller layers - Optimizing database queries (N+1, indexing, connection pooling) - Adding caching (Redis, in-memory, HTTP cache headers) - Setting up background jobs or async processing - Structuring error handling and validation for APIs - Building middleware (auth, logging, rate limiting) ## API Design Patterns ### RESTful API Structure ```typescript // ✅ Resource-based URLs GET /api/markets # List resources GET /api/markets/:id # Get single resource POST /api/markets # Create resource PUT /api/markets/:id # Replace resource PATCH /api/markets/:id # Update resource DELETE /api/markets/:id # Delete resource // ✅ Query parameters for filtering, sorting, pagination GET /api/market