ASP.NET Core is one of the most popular frameworks for building modern, cloud-ready, and scalable web applications. If you are preparing for an interview as a .NET developer, it’s crucial to have a strong grasp of ASP.NET Core concepts. Below, we’ve compiled some of the most commonly asked ASP.NET Core interview questions with answers that will help you crack your next interview.

1. What is ASP.NET Core?

ASP.NET Core is an open-source, cross-platform, high-performance framework developed by Microsoft for building modern web applications, APIs, and microservices. Unlike the traditional ASP.NET Framework, ASP.NET Core runs on multiple operating systems (Windows, macOS, Linux) and supports cloud-based deployments.

2. What are the key differences between ASP.NET and ASP.NET Core?

ASP.NET Core is cross-platform, while ASP.NET is Windows-only.
ASP.NET Core is modular and lightweight, whereas ASP.NET has a monolithic structure.
Dependency Injection (DI) is built-in in ASP.NET Core.
ASP.NET Core supports hosting on Kestrel, IIS, Apache, and Nginx, while ASP.NET primarily depends on IIS.
ASP.NET Core provides better performance and faster request handling.

3. What is Kestrel in ASP.NET Core?

Kestrel is a cross-platform, lightweight, and fast web server used by ASP.NET Core applications. It can run as a standalone server or behind a reverse proxy like IIS, Nginx, or Apache.

4. What are Middleware components in ASP.NET Core?

Middleware are software components arranged in a pipeline to handle requests and responses. Each middleware component can:

• Process an incoming HTTP request.

• Decide whether to pass the request to the next middleware.

• Modify the response before sending it back to the client.

Example: Authentication, Routing, Exception Handling, and Static Files are middleware components.

5. What is Dependency Injection (DI) in ASP.NET Core?

Dependency Injection is a design pattern that makes applications loosely coupled, testable, and maintainable. In ASP.NET Core, DI is built into the framework. Services can be registered in the Startup.cs file using:

• AddSingleton – A single instance for the whole application lifetime.

• AddScoped – One instance per request.

• AddTransient – A new instance each time it is requested.

6. What is the Startup.cs file used for?

The Startup.cs file is the entry point for configuring services and middleware in ASP.NET Core.
It usually contains two main methods:

• ConfigureServices(IServiceCollection services) → Used to register services (like DB Context, Identity, Authentication, etc.).

• Configure(IApplicationBuilder app, IHostingEnvironment env) → Used to define the request processing pipeline (middleware).

7. Explain the difference between appsettings.json and web.config.

• In traditional ASP.NET, web.config was used for configuration.

• In ASP.NET Core, appsettings.json is used for storing configuration data (connection strings, app settings, etc.).

• Unlike web.config, appsettings.json is JSON-based, environment-specific (e.g., appsettings.Development.json), and supports hierarchical configurations.

8. What is Entity Framework Core (EF Core)?

Entity Framework Core is an ORM (Object Relational Mapper) for .NET that allows developers to interact with databases using .NET objects instead of raw SQL queries. EF Core supports LINQ queries, change tracking, migrations, and multiple databases like SQL Server, MySQL, PostgreSQL, and SQLite.

9. What is the difference between .NET Core and .NET 5/6/7+?

• .NET Core was the original cross-platform framework.

• Starting with .NET 5, Microsoft unified .NET Core, .NET Framework, and Xamarin into a single platform known simply as .NET.

• .NET 6 and .NET 7 continue to improve performance, security, and cross-platform capabilities.

10. What are Tag Helpers in ASP.NET Core?

Tag Helpers are server-side components that allow developers to add server-side processing to HTML elements in Razor views.
Example: <form asp-action="Login"> automatically maps to the Login action in the controller.

11. What is Razor Pages in ASP.NET Core?

Razor Pages is a page-based programming model introduced in ASP.NET Core 2.0. It simplifies building web UI by combining HTML, C#, and Razor syntax in a single .cshtml file, making it easier for developers who prefer a page-centric model.

12. What is SignalR in ASP.NET Core?

SignalR is a library in ASP.NET Core used for adding real-time web functionality like chat applications, notifications, and live dashboards. It supports WebSockets, Server-Sent Events, and Long Polling.

13. How is Authentication handled in ASP.NET Core?

ASP.NET Core provides multiple authentication mechanisms:

• Cookie-based authentication

• JWT (JSON Web Token) authentication

• OAuth & OpenID Connect

• External providers like Google, Facebook, Microsoft, GitHub

14. What is gRPC in ASP.NET Core?

gRPC is a modern open-source RPC (Remote Procedure Call) framework supported in ASP.NET Core. It uses HTTP/2 for fast communication and Protocol Buffers (Protobuf) for serialization, making it ideal for microservices and high-performance applications.

15. What are some advantages of ASP.NET Core?

Cross-platform support
High performance with Kestrel
Unified MVC and Web API framework
Built-in Dependency Injection
Cloud-ready & lightweight deployment
Easy configuration with appsettings.json
Support for microservices and gRPC

Conclusion

ASP.NET Core has become the go-to framework for modern application development. Interviewers often focus on your understanding of core concepts like Middleware, Dependency Injection, EF Core, Authentication, and Performance optimization. By mastering these questions and answers, you’ll be much better prepared for your next ASP.NET Core interview.