Top 48 NestJS Interview Questions & Answers (2026)

01 What is NestJS? 02 What is a Module in NestJS? 03 What is a Controller in NestJS? 04 What is a Provider/Service in NestJS? 05 What is Dependency Injection in NestJS? 06 What are Decorators in NestJS? 07 What is the NestJS CLI and how is it used? 08 What are DTOs (Data Transfer Objects) in NestJS? 09 What is the ValidationPipe in NestJS? 10 What are Guards in NestJS? 11 What are Pipes in NestJS? 12 What are Interceptors in NestJS? 13 What are Exception Filters in NestJS? 14 What is the main.ts file in a NestJS application? 15 What is the difference between @Res() and res in NestJS? 16 What is the @nestjs/config module? 17 What is TypeORM integration in NestJS? 18 What is NestJS lifecycle hooks? 19 What is NestJS middleware vs guards vs interceptors? 20 What is the @nestjs/swagger module? 21 How do you create a custom decorator in NestJS?

01 How does NestJS dependency injection scoping work? 02 What are NestJS microservices and what transports are supported? 03 What is the ExecutionContext in NestJS? 04 How do you implement role-based access control (RBAC) in NestJS? 05 What is the Reflector in NestJS and how is it used? 06 How do you implement caching in NestJS? 07 What is event-driven architecture in NestJS using the EventEmitter? 08 How do you handle database transactions in NestJS with TypeORM? 09 What is NestJS GraphQL module? 10 How do you implement WebSocket support in NestJS? 11 What is the NestJS Queue module? 12 How do you write unit tests in NestJS? 13 What is the NestJS interceptor for response transformation? 14 What is the @nestjs/schedule module? 15 How does NestJS handle circular dependencies? 16 What is the @Global() decorator in NestJS? 17 How do you implement file uploads in NestJS?

01 What is the CQRS pattern and how does NestJS support it? 02 How do you implement gRPC in NestJS? 03 What is the NestJS Interceptor execution order and how do multiple interceptors interact? 04 How does NestJS handle graceful shutdown? 05 What is custom provider syntax in NestJS (useClass, useValue, useFactory)? 06 What is the difference between forRoot() and forFeature() in NestJS modules? 07 How do you implement health checks in NestJS? 08 What is NestJS's approach to multi-tenancy? 09 What is the cls-hooked/nestjs-cls module and when should you use it? 10 How do you optimize NestJS application performance for high traffic?