Top Interview Questions for .NET Developers in 2025

.NET continues to be one of the most popular frameworks for building scalable, high-performance web applications, APIs, and desktop applications. As organizations seek skilled .NET developers, the demand for professionals with in-depth knowledge of the framework is higher than ever. If you're preparing for a .NET developer interview in 2025, it's important to familiarize yourself with the top questions you might face. In this blog, we'll explore the top interview questions for .NET developers and provide tips to help you ace them.

WEB DEVELOPMENTINTERVIEW PREPARATION

1/11/20254 min read

1. What Is .NET and How Does It Work?

One of the first questions you'll encounter in a .NET interview is a basic explanation of what .NET is and its key features.

.NET is a free, open-source framework developed by Microsoft for building a wide range of applications, including web, mobile, desktop, and cloud-based solutions. The framework supports multiple programming languages, including C#, F#, and Visual Basic. It works across different platforms (Windows, macOS, and Linux) with the .NET Core and .NET 5/6/7 runtime environments.

2. What Is the Difference Between .NET Core and .NET Framework?

Understanding the difference between .NET Core and .NET Framework is essential for .NET developers. This question tests your knowledge of the framework’s evolution and the advantages of .NET Core.

  • .NET Framework: The original version of the .NET platform that primarily runs on Windows. It includes a large set of libraries and tools for building Windows-based applications.

  • .NET Core: A cross-platform, open-source version of the .NET framework. It allows developers to build applications that run on Windows, Linux, and macOS. .NET Core is lightweight, modular, and designed for modern cloud-based applications.

With .NET 5 and later versions, Microsoft has unified .NET Core and .NET Framework into a single platform known as just .NET.

3. What Are Assemblies in .NET?

Assemblies are a fundamental part of .NET applications. Interviewers will often ask this question to test your knowledge of the .NET compilation and deployment process.

An assembly is a compiled code library used by .NET applications. It contains metadata about the types and resources in an application, as well as the compiled code. There are two types of assemblies:

  • Private Assemblies: Used by a single application.

  • Shared Assemblies: Can be shared across multiple applications.

Assemblies are crucial for versioning, security, and deployment in .NET applications.

4. What Is the Common Language Runtime (CLR)?

The CLR is the runtime environment of .NET applications, providing important features like memory management, garbage collection, exception handling, and type safety. This question is typically asked to assess your understanding of how .NET applications are executed.

The CLR compiles the Intermediate Language (IL) code into native code and manages the execution of code. It also provides features like just-in-time (JIT) compilation, security, and debugging support.

5. What Is the Difference Between ref and out Parameters in C#?

This question tests your understanding of parameter passing in C#. The ref and out keywords are used to pass arguments by reference, but they have key differences.

  • ref: The parameter must be initialized before it is passed into the method. It allows for both input and output of data.

  • out: The parameter does not need to be initialized before being passed. It is used to return data from a method.

You should provide an example of both ref and out to explain the concept.

6. What Is the Garbage Collector in .NET?

The Garbage Collector (GC) in .NET is responsible for automatically managing memory by reclaiming memory that is no longer in use by the application. Interviewers often ask about the garbage collection process to assess your understanding of memory management.

The GC runs in the background and frees up memory by removing objects that are no longer referenced by the application. This helps reduce memory leaks and improves application performance. The process is automatic, but developers should still be mindful of managing resources efficiently.

7. What Is LINQ in C# and How Does It Work?

LINQ (Language Integrated Query) is a powerful feature of C# that allows developers to query collections and databases in a declarative manner. Interviewers often ask about LINQ to assess your ability to work with data in .NET applications.

LINQ allows developers to perform queries directly in C# code, making it easier to manipulate and retrieve data from various sources, such as arrays, collections, and databases. It simplifies complex data operations and improves code readability.

Example of a LINQ query:

csharp

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var result = from person in people where person.Age > 18 select person;

8. What Are Delegates and Events in C#?

Delegates and events are crucial concepts in C# for implementing event-driven programming. You can expect interviewers to ask about their roles and how they are used.

  • Delegate: A delegate is a type-safe function pointer that can reference methods with a particular signature. It allows methods to be passed as parameters or returned as values.

  • Event: An event is a way to notify other parts of the application when a particular action occurs. Events are often used in combination with delegates to create custom events in applications.

You should explain how delegates and events work together in creating event-driven systems.

9. What Is Dependency Injection in .NET?

Dependency Injection (DI) is a design pattern used to reduce coupling between components in an application. It is commonly used in .NET applications, especially in ASP.NET Core.

DI allows you to inject dependencies (such as services or objects) into a class, rather than hardcoding them within the class. This makes the application more modular, easier to test, and more maintainable.

In .NET Core, DI is built into the framework and is often used with the ConfigureServices method to register services for dependency injection.

10. What Is ASP.NET Core and How Is It Different from ASP.NET?

ASP.NET is a popular framework for building web applications, and ASP.NET Core is the modern, cross-platform version of ASP.NET. Interviewers may ask about the differences between the two.

  • ASP.NET: A framework that runs on the Windows operating system and is used to build web applications and services.

  • ASP.NET Core: A cross-platform, open-source framework that can run on Windows, Linux, and macOS. ASP.NET Core is faster, more modular, and has improved support for modern web development patterns like microservices.

ASP.NET Core is also highly optimized for cloud environments and is used to build high-performance APIs and web applications.

11. What Are Middlewares in ASP.NET Core?

In ASP.NET Core, middleware is software that is assembled into an application pipeline to handle requests and responses. Middleware can perform tasks like authentication, logging, error handling, or modifying requests before they reach the controller.

You should explain how to configure middleware in the Startup.cs file and how it helps with the request-response lifecycle in ASP.NET Core applications.

12. What Is Entity Framework and How Does It Work?

Entity Framework (EF) is an Object-Relational Mapper (ORM) that allows developers to interact with databases using C# objects. It eliminates the need for writing complex SQL queries by providing an abstraction layer over the database.

EF allows developers to perform CRUD (Create, Read, Update, Delete) operations through C# code, making data access more intuitive. EF Core is the modern, cross-platform version of Entity Framework.

Conclusion

.NET remains one of the most powerful and flexible frameworks for building modern applications. By preparing for these common .NET interview questions, you’ll be well-equipped to tackle your next .NET developer interview in 2025 and beyond.

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