NestJS for backend code

Overview

Comprehensive best practices guide for backend code or NestJS applications. Contains references across different categories, prioritized by impact to guide automated refactoring and code generation.

Capabilities:

• Guide writing of NestJS modules, controllers, and services with proper patterns.
• Apply architecture, dependency injection, error handling, security, and performance best practices.
• Drive automated refactoring and code generation, prioritized by impact.
• Implements the GREEN and REFACTOR phases of TDD.

Limitations:

• Guidance/reference only — does not scaffold or run code by itself.
• Focused on NestJS backend code; not for frontend or non-NestJS stacks.
• Testing is out of scope for this skill, not for tests.

Prerequisites

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

Examples

Read individual reference files as if they were rules and get detailed explanations and code examples:

references/arch-avoid-circular-deps.md
references/security-validate-all-input.md
references/_sections.md

Each reference file contains:

• Brief explanation of why it matters
• Incorrect code example with explanation
• Correct code example with explanation
• Additional context and references

References

For more details, consult these reference files (loaded on demand):

1. Architecture (CRITICAL)

• references/arch-avoid-circular-deps.md - Avoid circular module dependencies
• references/arch-feature-modules.md - Organize by feature, not technical layer
• references/arch-module-sharing.md - Proper module exports/imports, avoid duplicate providers
• references/arch-single-responsibility.md - Focused services over "god services"
• references/arch-use-repository-pattern.md - Abstract database logic for testability
• references/arch-use-events.md - Event-driven architecture for decoupling
• references/arch-hexagonal-ddd-structure.md - Structure modules with DDD + hexagonal architecture (ports & adapters)

2. Dependency Injection (CRITICAL)

• references/di-avoid-service-locator.md - Avoid service locator anti-pattern
• references/di-interface-segregation.md - Interface Segregation Principle (ISP)
• references/di-liskov-substitution.md - Liskov Substitution Principle (LSP)
• references/di-prefer-constructor-injection.md - Constructor over property injection
• references/di-scope-awareness.md - Understand singleton/request/transient scopes
• references/di-use-interfaces-tokens.md - Use injection tokens for interfaces

3. Error Handling (HIGH)

• references/error-use-exception-filters.md - Centralized exception handling
• references/error-throw-http-exceptions.md - Use NestJS HTTP exceptions
• references/error-handle-async-errors.md - Handle async errors properly

4. Security (HIGH)

• references/security-auth-jwt.md - Secure JWT authentication
• references/security-validate-all-input.md - Validate with class-validator
• references/security-use-guards.md - Authentication and authorization guards
• references/security-sanitize-output.md - Prevent XSS attacks
• references/security-rate-limiting.md - Implement rate limiting

5. Performance (HIGH)

• references/perf-async-hooks.md - Proper async lifecycle hooks
• references/perf-use-caching.md - Implement caching strategies
• references/perf-optimize-database.md - Optimize database queries
• references/perf-lazy-loading.md - Lazy load modules for faster startup

6. Database & ORM (MEDIUM-HIGH)

• references/db-use-transactions.md - Transaction management
• references/db-avoid-n-plus-one.md - Avoid N+1 query problems
• references/db-use-migrations.md - Use migrations for schema changes

7. API Design (MEDIUM)

• references/api-use-dto-serialization.md - DTO and response serialization
• references/api-use-interceptors.md - Cross-cutting concerns
• references/api-versioning.md - API versioning strategies
• references/api-use-pipes.md - Input transformation with pipes

8. Microservices (MEDIUM)

• references/micro-use-patterns.md - Message and event patterns
• references/micro-use-health-checks.md - Health checks for orchestration
• references/micro-use-queues.md - Background job processing

9. DevOps & Deployment (LOW-MEDIUM)

• references/devops-use-config-module.md - Environment configuration
• references/devops-use-logging.md - Structured logging
• references/devops-graceful-shutdown.md - Zero-downtime deployments

These files are only loaded if the agent needs additional context.