Preparing for a .NET interview requires strong understanding of core concepts, real-world implementation scenarios, and architectural best practices. Most .NET interview questions focus on fundamentals such as CLR, C#, ASP.NET Core, Entity Framework Core, dependency injection, REST API development, and modern architectural patterns like Clean Architecture and microservices. This guide covers the most frequently asked .NET interview questions along with concise explanations to help you prepare effectively.
Basic .NET Interview Questions
1. What is .NET?
.NET is a cross-platform development framework used to build web, desktop, cloud, mobile, and microservices applications. It provides a runtime environment called CLR and supports multiple languages such as C# and F#.
2. What is CLR?
CLR (Common Language Runtime) is the execution engine of .NET. It manages memory, garbage collection, exception handling, security, and JIT (Just-In-Time) compilation.
3. What is the difference between .NET Framework and .NET Core?
.NET Framework is Windows-only and traditionally used for legacy applications, while .NET Core (now unified under modern .NET) is cross-platform, lightweight, and optimized for cloud-native development.
4. What is CTS and CLS?
CTS (Common Type System) defines how data types are declared and managed in .NET, while CLS (Common Language Specification) ensures language interoperability across . NET-supported languages.
C# Interview Questions
5. What is the difference between abstract class and interface?
An abstract class can contain both implementation and abstract methods, while an interface defines only contracts. Modern C# supports default implementations in interfaces, but abstract classes still allow constructors and state.
6. What is dependency injection?
Dependency Injection (DI) is a design pattern that promotes loose coupling by injecting dependencies through constructors or properties instead of creating them directly.
7. What is the difference between IEnumerable and IQueryable?
IEnumerable executes queries in memory, while IQueryable translates queries into database-level execution, improving performance for large datasets.
8. What is async and await?
Async and await enable asynchronous programming in C#, allowing non-blocking operations and better performance in I/O-bound tasks such as API calls and database queries.
ASP.NET Core Interview Questions
9. What is middleware in ASP.NET Core?
Middleware components handle HTTP requests and responses in the ASP.NET Core pipeline. Each middleware can process, modify, or short-circuit requests.
10. What is the difference between authentication and authorization?
Authentication verifies user identity, while authorization determines user permissions.
11. How does routing work in ASP.NET Core?
Routing maps incoming HTTP requests to controllers and actions using attribute routing or conventional routing.
12. What is CORS?
CORS (Cross-Origin Resource Sharing) is a security feature that controls cross-origin HTTP requests between frontend and backend applications.
Entity Framework Core Interview Questions
13. What is DbContext?
DbContext is the primary class in Entity Framework Core that manages entity tracking, database connections, and CRUD operations.
14. What are migrations?
Migrations are a feature of EF Core that allow developers to evolve the database schema alongside application code.
15. What is lazy loading vs eager loading?
Lazy loading loads related data only when accessed, while eager loading retrieves related data upfront using Include().
Advanced .NET Interview Questions
16. What is Clean Architecture?
Clean Architecture is a layered design pattern that separates business logic from infrastructure and UI concerns, improving maintainability and testability.
17. What is microservices architecture?
Microservices architecture breaks an application into small, independent services that communicate via APIs, enabling scalability and independent deployments.
18. What is API versioning?
API versioning allows backward compatibility by maintaining multiple versions of an API.
19. What is logging in ASP.NET Core?
Logging captures application events for debugging, monitoring, and auditing purposes. Libraries like Serilog enhance structured logging.
20. What is the difference between Task and Thread?
Task represents an asynchronous operation managed by the Task Parallel Library, while Thread represents a low-level system thread.
Scenario-Based Interview Questions
21. How would you optimize a slow ASP.NET Core API?
Implement caching (Redis), optimize database queries, use async programming, apply indexing, and analyze logs for bottlenecks.
22. How would you secure a Web API?
Use JWT authentication, role-based authorization, HTTPS enforcement, input validation, and proper logging.
23. How do you handle global exception handling?
Implement custom middleware or use built-in exception handling mechanisms to standardize error responses.
24. How do you improve application performance?
Use distributed caching, asynchronous programming, efficient database queries, load balancing, and monitoring tools.
Tips to Prepare for .NET Interviews
Strengthen fundamentals of C# and OOP concepts
Build hands-on projects using ASP.NET Core
Practice REST API development
Understand dependency injection deeply
Learn clean architecture principles
Revise common design patterns
Prepare real-world scenarios and performance optimization strategies
Summary
The most asked .NET interview questions typically focus on core runtime concepts, C# fundamentals, ASP.NET Core architecture, Entity Framework Core, dependency injection, security mechanisms, performance optimization, and modern architectural patterns such as Clean Architecture and microservices. By mastering both theoretical concepts and practical implementation scenarios, candidates can confidently demonstrate their technical depth, problem-solving skills, and ability to build scalable and production-ready .NET applications during interviews.