NestJS NestJS provides a modular architecture with dependency injection, decorators for routing and validation, guards for auth, and interceptors for cross-cutting concerns. Installation Project Structure Module Entity DTOs with Validation Controller Service Guards App Module and Bootstrap Testing Key Patterns - One module per feature; import only what you need - Use with to strip unknown properties - Use guards for auth, interceptors for response mapping, filters for exceptions - Set in production — use TypeORM migrations instead - Use with for environment variables ---