100 Must-Know ASP.NET Web API Interview Questions and Answers 2025

ASP.NET Web API Fundamentals

1.
What is ASP.NET Web API and what is it used for?
2.
How does ASP.NET Web API differ from WCF and ASP.NET MVC?
3.
Explain RESTful services and how they relate to ASP.NET Web API.
4.
What are HTTP verbs and how are they used in Web API?
5.
How do you create a basic Web API controller?
6.
Describe routing in ASP.NET Web API.
7.
How are requests mapped to actions in Web API?
8.
What is content negotiation in the context of Web API?
9.
What data formats does Web API support by default for response data?
10.
How do you secure a Web API?

ASP.NET Web API Configuration and Hosting

11.
How can you host an ASP.NET Web API application?
12.
What is OWIN and how does it relate to Web API?
13.
Explain the difference between self-hosting and IIS hosting in Web API.
14.
How do you configure CORS in Web API?
15.
What is attribute routing and how does it improve the Web API?
16.
How do you handle versioning in Web API?

ASP.NET Web API Request and Response

17.
How do you handle different response status codes in Web API?
18.
What is IHttpActionResult, and how does it work in action results?
19.
How do you read data from the query string in Web API?
20.
Explain the use of Request and Response message classes.
21.
How can you enforce SSL in a Web API action?
22.
What is Model Binding in Web API and how is it different from MVC?
23.
How do you bind complex types in Web API?

ASP.NET Web API Serialization and Media Formats

24.
How do you customize serialization in Web API?
25.
What are media type formatters in Web API?
26.
How do you support XML or JSON, or other formats as a response in Web API?
27.
What is BSON and how can it be used with Web API?
28.
How do you return a custom response format from an action?

ASP.NET Web API Action Filters and Handlers

29.
What are DelegatingHandlers in Web API?
30.
How do you implement Action Filters in Web API?
31.
Explain the difference between action filters and authorization filters.
32.
How can you implement custom authentication in Web API?
33.
What is message lifecycle in ASP.NET Web API?

ASP.NET Web API Dependency Injection and Testing

34.
How do you implement Dependency Injection in ASP.NET Web API?
35.
What frameworks are useful for testing Web API applications?
36.
Explain the process of unit testing in ASP.NET Web API.

ASP.NET Web API and Entity Framework

37.
How can you integrate Entity Framework with Web API?
38.
Describe the best practices for using Entity Framework with Web API.

Advanced ASP.NET Web API Topics

39.
How does Web API implement OData?
40.
What are action selectors?
41.
Explain the use of Exception Filters in your API.
42.
What are the benefits of using async and await in Web API?
43.
How can you handle file uploads in Web API?
44.
Discuss SignalR and its integration with ASP.NET Web API.

ASP.NET Web API performance

45.
What are some performance optimization strategies for Web API?
46.
How do you implement caching in Web API?
47.
What role does HttpResponseMessage play in Web API performance?

ASP.NET Web API Security

48.
What are the different ways to authenticate users in Web API?
49.
How do you implement OAuth2 authorization in Web API?
50.
Explain token-based authentication in Web API.

ASP.NET Web API Client-Side

51.
How can a client consume a Web API?
52.
Discuss different client libraries available for accessing ASP.NET Web API.
53.
What is Swagger, and how does it integrate with Web API?

ASP.NET Web API Troubleshooting

54.
How do you handle errors globally in ASP.NET Web API?
55.
What is a common cause for a 404 not found error in Web API and how can it be resolved?

ASP.NET Web API Best Practices

56.
Discuss some best practices for API versioning.
57.
How can you make your Web API more RESTful?
58.
What are some common security issues to be aware of when developing a Web API?
97.
What are some common patterns used in API development?
98.
How do you manage large-scale API development and multiple teams?
99.
Describe some anti-patterns to avoid in Web API development.

ASP.NET Web API Design and Architecture

59.
When should you use ASP.NET Web API over other technologies?
60.
How can you design a scalable API using ASP.NET Web API?
61.
Describe a microservices architecture with reference to ASP.NET Web API.
62.
What is the Repository pattern and how does it apply to Web API?

Miscellaneous Topics on ASP.NET Web API

63.
What is Web API OWIN middleware?
64.
How can you document your Web API?
65.
Describe how you would implement rate limiting in ASP.NET Web API.

ASP.NET Web API and Globalization

66.
How do you support multiple languages in Web API?
67.
What is localization and how can it be applied in Web API?

ASP.NET Web API Routing

68.
Explain convention-based routing in Web API.
69.
What are the limitations of convention-based routing and how can they be overcome?
70.
How can you define optional parameters in the route?
71.
What is route constraint in Web API and how do you use it?

ASP.NET Web API and Data Transfer Objects (DTOs)

72.
What are DTOs and why are they important in Web API?
73.
Explain how to use AutoMapper in ASP.NET Web API.

ASP.NET Web API Action Results

74.
What are the advantages of using IHttpActionResult?
75.
Differentiate between Ok, BadRequest, NotFound, and other action results in Web API.

ASP.NET Web API and Asynchronous Programming

76.
Discuss the benefits and risks of using asynchronous controllers in Web API.
77.
Give an example of how to implement an asynchronous action in Web API.

ASP.NET Web API and Content Negotiation

78.
Define content negotiation and its role in a Web API application.
79.
How do you force Web API to return a specific content type?

ASP.NET Web API and Security Features

80.
How do you implement claims-based authentication in Web API?
81.
Explain Cross-Site Request Forgery (CSRF) protection in Web API.
82.
How does anti-forgery token work in Web API and when should you use it?

ASP.NET Web API Caching

83.
What are the different caching mechanisms available to a Web API?
84.
How does server-side caching work in Web API?

ASP.NET Web API and Middleware

85.
Explain the role of middleware in the ASP.NET Web API pipeline.
86.
How can middleware be used to implement cross-cutting concerns?

ASP.NET Web API and Deployment

87.
What are some considerations when deploying a Web API to Azure?
88.
How do you enable HTTPS for a Web API on Azure?

ASP.NET Web API Advanced Topics

89.
What are HATEOAS and its importance in RESTful APIs?
90.
Explain how to implement HATEOAS in an ASP.NET Web API.

ASP.NET Web API and Monitoring

91.
What tools can you use to monitor the health and performance of your Web API?
92.
How can you log API requests and responses?

ASP.NET Web API Testing and Troubleshooting

93.
What approaches can you take to troubleshoot a failing Web API?
94.
How can integration testing be implemented for a Web API?

ASP.NET Web API and Interoperability

95.
How can you ensure your Web API is consumable by a wide range of clients?
96.
What is JSONP, and how can it be used with Web API?

ASP.NET Web API Emerging Technologies and Trends

100.
How can ASP.NET Web API leverage new technologies like Docker and Kubernetes?

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100 ASP.NET Web API interview questions

What is ASP.NET Web API and what is it used for?

How does ASP.NET Web API differ from WCF and ASP.NET MVC?

Explain RESTful services and how they relate to ASP.NET Web API.

What are HTTP verbs and how are they used in Web API?

How do you create a basic Web API controller?

Describe routing in ASP.NET Web API.

How are requests mapped to actions in Web API?

What is content negotiation in the context of Web API?

What data formats does Web API support by default for response data?

How do you secure a Web API?

How can you host an ASP.NET Web API application?

What is OWIN and how does it relate to Web API?

Explain the difference between self-hosting and IIS hosting in Web API.

How do you configure CORS in Web API?

What is attribute routing and how does it improve the Web API?

How do you handle versioning in Web API?

How do you handle different response status codes in Web API?

What is IHttpActionResult, and how does it work in action results?

How do you read data from the query string in Web API?

Explain the use of Request and Response message classes.

How can you enforce SSL in a Web API action?

What is Model Binding in Web API and how is it different from MVC?

How do you bind complex types in Web API?

How do you customize serialization in Web API?

What are media type formatters in Web API?

How do you support XML or JSON, or other formats as a response in Web API?

What is BSON and how can it be used with Web API?

How do you return a custom response format from an action?

What are DelegatingHandlers in Web API?

How do you implement Action Filters in Web API?

Explain the difference between action filters and authorization filters.

How can you implement custom authentication in Web API?

What is message lifecycle in ASP.NET Web API?

How do you implement Dependency Injection in ASP.NET Web API?

What frameworks are useful for testing Web API applications?

Explain the process of unit testing in ASP.NET Web API.

How can you integrate Entity Framework with Web API?

Describe the best practices for using Entity Framework with Web API.

How does Web API implement OData?

What are action selectors?

Explain the use of Exception Filters in your API.

What are the benefits of using async and await in Web API?

How can you handle file uploads in Web API?

Discuss SignalR and its integration with ASP.NET Web API.

What are some performance optimization strategies for Web API?

How do you implement caching in Web API?

What role does HttpResponseMessage play in Web API performance?

What are the different ways to authenticate users in Web API?

How do you implement OAuth2 authorization in Web API?

Explain token-based authentication in Web API.

How can a client consume a Web API?

Discuss different client libraries available for accessing ASP.NET Web API.

What is Swagger, and how does it integrate with Web API?

How do you handle errors globally in ASP.NET Web API?

What is a common cause for a 404 not found error in Web API and how can it be resolved?

Discuss some best practices for API versioning.

How can you make your Web API more RESTful?

What are some common security issues to be aware of when developing a Web API?

What are some common patterns used in API development?

How do you manage large-scale API development and multiple teams?

Describe some anti-patterns to avoid in Web API development.

When should you use ASP.NET Web API over other technologies?

How can you design a scalable API using ASP.NET Web API?

Describe a microservices architecture with reference to ASP.NET Web API.

What is the Repository pattern and how does it apply to Web API?

What is Web API OWIN middleware?

How can you document your Web API?

Describe how you would implement rate limiting in ASP.NET Web API.

How do you support multiple languages in Web API?

What is localization and how can it be applied in Web API?

Explain convention-based routing in Web API.

What are the limitations of convention-based routing and how can they be overcome?

How can you define optional parameters in the route?

What is route constraint in Web API and how do you use it?

What are DTOs and why are they important in Web API?

Explain how to use AutoMapper in ASP.NET Web API.

What are the advantages of using IHttpActionResult?

Differentiate between `Ok`, `BadRequest`, `NotFound`, and other action results in Web API.