260223:1415 20260223 nextJS & nestJS Best pratices

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+---
+name: nestjs-best-practices
+description: NestJS best practices and architecture patterns for building production-ready applications. This skill should be used when writing, reviewing, or refactoring NestJS code to ensure proper patterns for modules, dependency injection, security, and performance.
+license: MIT
+metadata:
+  author: Kadajett
+  version: "1.1.0"
+---
+
+# 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`