Top 20 ASP.NET Web API Interview Questions

When you’re preparing for an interview for a position that involves working with ASP.NET Web API, it’s important to be familiar with the technology and its features. In this post, we’ll go through some of the most common interview questions you might encounter, along with the best ways to answer them.

Top 20 ASP.NET Web API Interview Questions

1. What is ASP.NET Web API?
ASP.NET Web API is a framework that allows you to build HTTP services that can be accessed by different clients. It’s a lightweight platform for creating RESTful services, which can be used to provide data to web and mobile applications.

2. What are some of the benefits of using ASP.NET Web API?
ASP.NET Web API is easy to use and configure, it’s extensible and flexible, and it provides a good level of performance. It also supports a wide range of media types and can be used with a variety of web technologies, making it a great choice for building web applications.

3. What is the difference between ASP.NET Web API and WCF?
While both ASP.NET Web API and Windows Communication Foundation (WCF) can be used to create web services, they have some fundamental differences. Web API is more lightweight and is designed to work with HTTP services, while WCF is more heavyweight and can be used with a range of communication protocols.

4. What is REST?
REST stands for Representational State Transfer, which is a style of software architecture that is used to create web services. RESTful services are designed to be simple, scalable, and flexible, and they use HTTP to exchange data between clients and servers.

5. What is HTTP?
HTTP stands for Hypertext Transfer Protocol, which is the protocol used by the World Wide Web to exchange data between web servers and clients. It’s the foundation of the modern web and is used by web browsers, servers, and other applications to communicate with each other.

6. What is a GET request?
A GET request is an HTTP request that is used to retrieve data from a web server. It’s one of the most common types of requests used by web browsers and can be used to retrieve information from a range of web resources.

7. What is a POST request?
A POST request is an HTTP request that is used to submit data to a web server. It’s often used to create new resources or to update existing ones, and can be used to send data in a variety of formats, including JSON and XML.

8. What is a JSON?
JSON stands for JavaScript Object Notation, which is a lightweight data interchange format that is easy to read and write. It’s used to transmit data between a client and a server, and is commonly used in web applications.

9. What is XML?
XML stands for Extensible Markup Language, which is a markup language that is used to store and exchange data in a format that is both human-readable and machine-readable. It’s commonly used in web services and other applications that require structured data.

10. What is a Model in ASP.NET Web API?
A model is a class that is used to represent the data that is being exchanged between a client and a server in an ASP.NET Web API application. It’s used to serialize and deserialize data, and can be used to perform validation and other tasks.

11. What is a Controller in ASP.NET Web API?
A controller is a class that is used to define the actions that can be performed by an ASP.NET Web API application. It’s used to handle requests from clients, and can be used to perform a wide range of tasks, including data validation and error handling.

12. What is an Action in ASP.NET Web API?
An action is a method on a Web API controller that handles HTTP requests. Each action corresponds to a specific HTTP verb (such as GET or POST) and URL path. When a request is made to an API endpoint, Web API maps the request to the appropriate action based on the request’s HTTP verb and URL path. Actions can return any type of data, including strongly typed objects, HttpResponseMessage objects, and IHttpActionResult objects.

13. What is the role of a message handler in ASP.NET Web API?
A message handler is responsible for processing incoming HTTP requests and outgoing HTTP responses. Message handlers can modify the request or response headers, add content to the response body, or perform any other processing necessary to handle the request or response. Message handlers are executed in a pipeline, where each handler in the pipeline has an opportunity to process the request or response.

14. What is the difference between IQueryable and IEnumerable in ASP.NET Web API?
IQueryable is used to build a LINQ query that can be executed against a data source, while IEnumerable is used to represent a collection of objects in memory. IQueryable allows you to create a query that is executed by a data source (such as a SQL Server database), which can result in improved performance for large data sets.

15. What is the purpose of Web API filters?
Web API filters are used to apply cross-cutting concerns to Web API actions. Filters can be used to perform authentication, validation, logging, and other common tasks that need to be applied to multiple actions. Filters can be applied at the global level (to all actions), at the controller level (to all actions in a specific controller), or at the action level (to a specific action).

16. What is the difference between IHttpActionResult and HttpResponseMessage in ASP.NET Web API?
IHttpActionResult is a return type that allows you to create a strongly typed HTTP response that can be returned from an action. IHttpActionResult is a more flexible and testable way to return HTTP responses from Web API actions, because it allows you to encapsulate the response logic in a separate class that can be easily unit tested. HttpResponseMessage, on the other hand, is a more low-level way to create HTTP responses, and is typically used when you need to have full control over the response headers and content.

17. What is attribute routing in ASP.NET Web API?
Attribute routing is a feature in ASP.NET Web API that allows you to define your API routes using attributes on your controller actions. Attribute routing gives you more control over your routing, and can be more expressive and readable than convention-based routing. With attribute routing, you can define multiple routes for the same action, and you can also use route parameters to define dynamic segments in your URLs.

18. What is the role of a formatter in ASP.NET Web API?
A formatter is responsible for serializing and deserializing data between the Web API controller and the HTTP request or response. Formatters can handle a variety of data formats, including XML, JSON, and other media types. Web API includes several built-in formatters, and you can also create your own custom formatters if you need to handle a specific data format.

19. What is dependency injection in ASP.NET Web API?
Dependency injection is a design pattern that allows you to decouple the creation of an object from its dependencies. In ASP.NET Web API, dependency injection can be used to inject dependencies (such as data repositories or logging components) into your Web API controllers, message handlers, or other components. Dependency injection allows you to create more modular and testable code, and can make it easier to swap out components or modify your application’s behavior.

20. What is the role of middleware in ASP.NET Web API?
Middleware plays an important role in ASP.NET Web API by providing a way to extend and customize the request/response processing pipeline. Middleware components are responsible for performing tasks such as authentication, logging, compression, caching, and more. They can be used to modify the request or response, add headers or status codes, and even short-circuit the pipeline by returning a response directly.


In conclusion, the ASP.NET Web API is a powerful tool for building web services and APIs in the .NET framework. Its flexibility and compatibility with various platforms make it a popular choice among developers. Whether you are a beginner or an hire dedicated NET developer, it is essential to prepare well for ASP.NET Web API interviews.

Knowing the answers to commonly asked questions can help you demonstrate your knowledge and expertise in the field. The questions listed in this article cover some of the most important concepts and features of the framework. By studying and practicing these questions, you can boost your confidence and increase your chances of success in your ASP.NET Web API interviews.


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