nestjs-best-practices

# NestJS Best Practices Comprehensive best practices guide for NestJS applications. Contains 40 rules across 10 categories, prioritized by impact to guide automated refactoring and code generation. ## When to Apply Reference these guidelines when: - Writing new NestJS modules, controllers, or services - Implementing authentication and authorization - Reviewing code for architecture and security issues - Refactoring existing NestJS codebases - Optimizing performance or database queries - Building microservices architectures ## Rule Categories by Priority | Priority | Category | Impact | Prefix | | -------- | -------------------- | ----------- | ----------- | | 1 | Architecture | CRITICAL | `arch-` | | 2 | Dependency Injection | CRITICAL | `di-` | | 3 | Error Handling | HIGH | `error-` | | 4 | Security | HIGH | `security-` | | 5 | Performance | HIGH | `perf-` | | 6 | Testing | MEDIUM-HIGH | `test-` | | 7 | Database & ORM | MEDIUM-HIGH | `db-` | | 8 | API Design | MEDIUM | `api-` | | 9 | Microservices | MEDIUM | `micro-` | | 10 | DevOps & Deployment | LOW-MEDIUM | `devops-` | ## Quick Reference ### 1. Architecture (CRITICAL) - `arch-avoid-circular-deps` - Avoid circular module dependencies - `arch-feature-modules` - Organize by feature, not technical layer - `arch-module-sharing` - Proper module exports/imports, avoid duplicate providers - `arch-single-responsibility` - Focused services over "god services" - `arch-use-repository-pattern` - Abstract database logic for testability - `arch-use-events` - Event-driven architecture for decoupling ### 2. Dependency Injection (CRITICAL) - `di-avoid-service-locator` - Avoid service locator anti-pattern - `di-interface-segregation` - Interface Segregation Principle (ISP) - `di-liskov-substitution` - Liskov Substitution Principle (LSP) - `di-prefer-constructor-injection` - Constructor over property injection - `di-scope-awareness` - Understand singleton/request/transient scopes - `di-use-interfaces-tokens` - Use injection tokens for interfaces ### 3. Error Handling (HIGH) - `error-use-exception-filters` - Centralized exception handling - `error-throw-http-exceptions` - Use NestJS HTTP exceptions - `error-handle-async-errors` - Handle async errors properly ### 4. Security (HIGH) - `security-auth-jwt` - Secure JWT authentication - `security-validate-all-input` - Validate with class-validator - `security-use-guards` - Authentication and authorization guards - `security-sanitize-output` - Prevent XSS attacks - `security-rate-limiting` - Implement rate limiting ### 5. Performance (HIGH) - `perf-async-hooks` - Proper async lifecycle hooks - `perf-use-caching` - Implement caching strategies - `perf-optimize-database` - Optimize database queries - `perf-lazy-loading` - Lazy load modules for faster startup ### 6. Testing (MEDIUM-HIGH) - `test-use-testing-module` - Use NestJS testing utilities - `test-e2e-supertest` - E2E testing with Supertest - `test-mock-external-services` - Mock external dependencies ### 7. Database & ORM (MEDIUM-HIGH) - `db-use-transactions` - Transaction management - `db-avoid-n-plus-one` - Avoid N+1 query problems - `db-use-migrations` - Use migrations for schema changes ### 8. API Design (MEDIUM) - `api-use-dto-serialization` - DTO and response serialization - `api-use-interceptors` - Cross-cutting concerns - `api-versioning` - API versioning strategies - `api-use-pipes` - Input transformation with pipes ### 9. Microservices (MEDIUM) - `micro-use-patterns` - Message and event patterns - `micro-use-health-checks` - Health checks for orchestration - `micro-use-queues` - Background job processing ### 10. DevOps & Deployment (LOW-MEDIUM) - `devops-use-config-module` - Environment configuration - `devops-use-logging` - Structured logging - `devops-graceful-shutdown` - Zero-downtime deployments ## How to Use Read individual rule files for detailed explanations and code examples: ``` rules/arch-avoid-circular-deps.md rules/security-validate-all-input.md rules/_sections.md ``` Each rule file contains: - Brief explanation of why it matters - Incorrect code example with explanation - Correct code example with explanation - Additional context and references ## Full Compiled Document For the complete guide with all rules expanded: `AGENTS.md`