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

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

Working Alongside Other Skills

This skill is a reference for NestJS conventions, not a workflow. When another skill (TDD, implementation, code review, bug diagnosis, architecture review) is driving the task in a NestJS project, keep following that skill's process and apply these rules to the code it produces:

• Writing tests: read the test- rules before choosing how to build the test module and mocks.
• Reviewing or refactoring: check the changed code against the arch-, di- and security- rules first.
• Designing new modules or endpoints: read the relevant arch-, api- and security-validate-all-input rules before writing code.

Read only the rule files relevant to the change, not all 40.

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 in a single document, see AGENTS.md in the repository.