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Top Web API Interview Questions and Answers (2023)

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APIs, or Application Programming Interfaces, are more important than ever in today's economy. APIs are everywhere, fueling our lives behind the scenes, even if we don't notice them.

Top Web API Interview Questions and Answers

APIs are used to deliver content by streaming services like Spotify and Netflix. APIs are used by automakers such as Tesla to distribute software upgrades. You've probably seen these API integrations everywhere, from logging in with Facebook to PayPal transactions. 

This article will go through 40+ Web API Interview Questions asked during interviews to help you prepare for your upcoming job interview.

Must Recommended Topic, Pandas Interview Questions

Web API Interview Questions for Beginners

1. What do you mean by ASP.Net Web API?

The ASP.Net Web API framework supports the structuring and consumption of HTTP-based services. Online API can be used by clients who work with mobile apps and web browsers.

2. What's the difference between a Web API and a REST API provided by WCF?

The main differences between Web API and WCF Rest API are:

  1. WCF REST API is best for Message Queue, one-way messaging, and duplex communication, while Web API is best for HTTP-based services.
  2. WCF supports SOAP and XML formats, while WEB API accepts any media format, including XML and JSON. 
  3. WCF is great for establishing service-oriented applications, while ASP.NET Web API is ideal for building HTTP services. 
  4. There is no configuration required to run Web API, but many setups are needed to operate WCF.

3. What are the key benefits of opting for Web API instead of WCF?

There are several benefits of opting for Web API instead of WCF:

  • Web API is simpler and more lightweight than WCF, making it easier to develop and maintain
  • Web API is designed around HTTP, making it suitable for web-based applications and adhering to REST principles
  • Web API supports a wide range of platforms, including .NET, Java, and more, promoting interoperability
  • Web API follows open standards like JSON and XML for data interchange

4. What are the benefits of using Rest in Web API?

There are several benefits of using REST in Web API:

  • REST is stateless, making it scalable and easy to manage
  • RESTful services can be consumed by various clients, including web browsers, mobile apps, and other devices
  • RESTful architecture simplifies communication through HTTP methods like GET, POST, PUT, and DELETE
  • RESTful services can handle large-scale applications efficiently

5. What is the purpose of ASP.Net Web API Routing?

This is one of the most frequent Web API Interview Questions.
Web API Routing determines the action and controller that should be called.
The following are some examples of integrating routing in a Web API: 

  • Routing based on attributes.
  • Routing based on convention. 

6. In the Web API, what are Media type formatters?

The Web API's Media type formatter includes the following:

  • MediaTypeFormatter: The primary class that handles serialising and deserializing of strongly-typed objects.
  • BefferedMediaTypeFormatter:  This helper class allows you to use an asynchronous formatter on top of the infrastructure for asynchronous formatters. 

7. What is the best way to secure an ASP.Net Web API?

To secure an ASP.Net Web API, we must first govern it and determine who has access to it and who does not. Anyone with access to the URL can use the Web API. 

8. What's the difference between an HTTP Get and an HTTP Post request?

HTTP has two important verbs: GET and POST. Let us know the difference between HTTP Get and an HTTP Post request

The Get parameters are included in the URL.The POST parameters are included in the body.
Do not make changes to the servers.Make changes to the Server.
A Get request is Idempotent.A Post request is non-idempotent.
Data is sent in plain text.Binary and text data are transmitted.

9. Is it possible to use Web API in combination with traditional ASP.Net Forms?

Web API may be utilised with ASP.Net Forms with ease. In the Global.asax file, you may add a Web API Controller and a route to the Application Start method.

10. In ASP.Net Web API, what are exception filters

The IExceptionFilters interface is implemented with the help of exception filters in the Web API. Their execution takes place when an action throws an exception at any point. 

11. Does The ASP.Net Web API return views?

No, because Web API generates an HTTP-based service, it is impossible. It's primarily found in MVC(Model View Controller) applications.

12. Which return types are commonly supported in Web API?

There are various commonly supported return types in Web API:

  1. JSON: JavaScript Object Notation is a popular format for data interchange
  2. XML: Extensible Markup Language is used for structured data representation
  3. Plain text: Simple text responses
  4. HTML: For rendering web pages

13. How can we ensure that the Web API only delivers data in JSON format?

Open the "WebApiConfig.cs" file and add the following line to verify that the web API only provides data in JSON format:

config.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue(“application/json”))

14. How can we deal with Web API errors?

The following classes can be used to handle errors or exceptions in the Web API:

  • Using HttpResponseException: This exception class assists in the return of the HTTP status code supplied in the exception Constructor.
  • Using HttpError: This exception class helps return a relevant error code to the client in a HttpResponseMessage.
  • Using Exception Filters: Exception filters catch unhandled exceptions or errors in Web API and can be used whenever the controller action function throws an unhandled error.

15. How can we use HTTPClient to consume a Web API?

The HTTPClient in the HTTPClient class was created to communicate with the ASP.Net Web API. We can use this HTTPClient class in either a console or an MVC application.

16. How can we enable HTTPs in Web API?

The HTTP protocol is used by ASP.Net Web API.  We can construct a class and obtain a class with AuthorizationFilterAttribute. Then check to see if the URL you've requested is HTTPS.

17. In ASP.Net Web API, how do you implement Basic Authentication?

In ASP.Net Web API, basic authentication can be achieved by sending a request with an Authorization header and the word Basic. The Authorization header in Basic Authentication contains the word Basic followed by a base 64 encoded string. The Basic Authentication syntax : Authorization: Basic username: password.

18. What is Web API Token-Based Authentication?

It's a method of securing .Net API.  Since it uses a signed token to authenticate users, it is also known as a token-based approach.

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Web API Interview Questions for Intermediate

19. In the.Net Web API, what is content negotiation?

In the ASP.Net Web API, content negotiation occurs on the server-side. This is useful for detecting the media type formatter, especially when responding to an incoming request.

20. What is the definition of ASP.Net identity?

Microsoft's membership management framework is called ASP.Net Identity. It is pretty simple to integrate with Web API. This can allow the development of a secure HTTP service.

21. What exactly is REST?

REST is the acronym for Representational State Transfer. This is an architectural pattern that facilitates data exchange in a distributed context. All services are treated as resources in the REST architectural pattern, and a client can access them using HTTP protocol methods such as PUT, GET, POST, and DELETE.

22. Which protocols does Web API support?

HTTP is the only protocol that Web API supports. As a result, it may be accessed by any client that understands the HTTP protocol.

23. What do MVC and Web API have in common?

Both MVC and Web API are dependent on the separation of concerns principle, and concepts like controllers, routing, and models are used in both MVC and Web API.

24. What are the main differences between MVC and Web API?

Ans: MVC is a framework for creating applications with user interfaces. In MVC, views are utilised to create a user interface. The Web API is used to build HTTP services. Other applications use the Web API methods to retrieve data.

25. How to use Attribute Routing?

The MapHttpAttributeRoutes() method in the WebApi config file can be used to enable attribute routing.

public static void Register(HttpConfiguration config)
// Web API routes
// Other Web API configuration not shown.

26. What media types does Web API support by default?

Web API supports the following media formats by default: XML, form URL encoded data, JSON, and BSON. Other media formats can be supported by writing a media formatter.

27. In Web API, what do you mean by TestAPI?

In the context of Web API, TestAPI refers to a utility library that enables developers to create testing tools and automate tests for .Net applications.

28. What is the meaning of an HTTP status code?

HTTP status codes are three-digit integers that the server returns in response to the client's request, with each number indicating a meaning.

29. What is the Delegatinghandler purpose?

Ans: DelegatingHandler is a method for creating a custom server-side HTTP message handler and chaining message handlers in the ASI.Net Web API.

30. What exactly is the difference between XML and JSON?

The EXtensible Markup Language (XML) is a data storage and transmission format. JSON stands for JavaScript Object Notation, and it's a format for storing and transmitting data from a server to a web page.
XML does not do much more than store data in a specified format, whereas JSON is a lightweight and easy-to-understand data storage format extensively used in JavaScript.

31. What exactly do you mean when you say "caching"?

The practice of temporarily keeping data in cache for future use is known as caching. It stores copies of all commonly used data and files, allowing the website to render more quickly. It also aids scalability by enabling data to be directly accessed from memory when required in the future.
IMemoryCache is the most basic cache in the ASP.Net Web API. 

32. What is HMAC Authentication, and how does it work?

HMAC is the abbreviation for Hash-based Message Authentication Code. We need to comprehend two things from the complete form of HMAC: one is Message Authentication Code, and the other is Hash-Based. So, HMAC is a Hash Function-based approach for generating a Message Authentication Code.

33. Why is HMAC Authentication required in Web APIs?

The following are the most common uses of HMAC Authentication in Web API.

  • Data integrity: It refers to the fact that the data delivered from the client to the server has not been tampered with.
  • Request origination: A trusted client sends the request to the server.
  • Not a replay request: The request was not intercepted and repeated by an intruder.

Web API Interview Questions for Experienced

34. What is the difference between SOAP and RESTful APIs?

NameSimple Object Access ProtocolRepresentational State Transfer
ProtocolSOAP is a protocol that uses XML for data exchange.RESTful APIs are based on the HTTP protocol
StructureSOAP messages are structured with a header and a body.RESTful APIs use URIs to identify resources and HTTP methods
FlexibilitySOAP is a more rigid protocol.RESTful APIs are more flexible and wider variety of APIs are made
Use Caseused in enterprise software where security and reliability are important used in modern web applications where simplicity and scalability are important.

35. Explain the difference between REST API and RESTful API.

It is an API that conforms to REST principles.A specific type of REST API that strictly adheres to REST principles.
It may or may not strictly follow all REST constraints.                                                                                                                        It strictly follows REST constraints, such as statelessness, resource-based URIs, and proper HTTP methods.
It is potentially less strict and may allow some flexibility in design.It is more rigid in design and strictly follows REST conventions.
It offers flexibility in choosing how to structure resources and interactions.It offers less flexibility but ensures standardized resource naming and interactions.
It provides more freedom in designing endpoints and actions.It enforces uniformity and consistency in endpoint design.

36. What does CORS stand for, and how does it relate to Web API security?

CORS stands for Cross-Origin Resource Sharing. It is a security feature implemented by web browsers to control cross-origin requests. In the context of Web API, CORS policies determine whether a web application from one domain can access resources hosted on another domain. Properly configuring CORS settings in a Web API helps enhance security by preventing unauthorized access.

37. How to handle authentication and authorization in a web API?

Authentication is the process of verifying the identity of a user. This is typically done by requiring the user to provide a username and password. Some other methods used for authorization are OAuth or API keys. 
Once the user has been authenticated, the web API can then determine what resources they are allowed to access. This is done through authorization.

Let's see some common authorization methods:

  • Role-based access control (RBAC) assigns users to roles, and each role has a set of permissions that determine what resources the user is allowed to access. For example, a user with the role of "admin" might be allowed to access all resources, while a user with the role of "user" might only be allowed to access certain resources.
  • Attribute-based access control (ABAC) allows permissions to be assigned to users based on attributes, such as their department, job title etc. For example, a user working in the sales department might be allowed to access all sales resources, irrespective of their role.

38. What is versioning in web APIs and its importance?

Versioning is the practice of assigning a unique identifier or number to different versions of an API.

let's see the importance of versioning:

  • Backward compatibility: Versioning ensures existing clients can still function properly when changes are made to the API.
  • Controlled updates: Versioning provides control over when and how updates are applied to the API.
  • Client Choice: Clients can select the API version that best meets their needs and compatibility.
  • Stability and predictability: Versioning maintains a more stable and predictable development experience.

39. How to handle errors and exceptions in web API?

Points to consider when dealing with errors and exceptions in a web API:

  • Use the correct HTTP status codes and provide specific error messages. 
  • Use structured error responses.
  • Implement logging to track errors.
  • Correctly handle input validation errors.
  • Test error scenarios thoroughly.

40. What is the use of caching in web APIs? 

Caching improves performance by storing frequently requested data on the client side. Hence, reducing the need to fetch data from the original source. It improves the user experience as it contributes to faster response times.

41. How to ensure the security of a web API? 

To ensure security, we should be using HTTPS, strong authentication and authorization mechanisms, implementing input validation and protecting against common vulnerabilities like SQL injection and cross-site scripting (XSS).

42. Define rate limiting? 

Rate limiting restricts the number of requests a client can make within a specific timeframe, preventing abuse and ensuring fair resource allocation for all users.

43. How to handle API versioning without changing the URL structure? 

Let's see some of the ways to handle API versioning:

  • Request headers: Clients specify the API version in the request headers instead of the URL.
  • Content negotiation: Use content negotiation techniques like the Accept header to allow clients to specify a preferred version.
  • Query parameters: Include a version query parameter in the URL to indicate the desired API version.
  • Response formats: Clients can request specific formats corresponding to different API versions.

44. What is the role of API documentation in web API development? 

The API documentation provides clear guidelines and instructions on how to interact with the API, including endpoints, parameters, request/response formats, and examples.

45. How to handle data pagination in a web API? 

Steps for handling data pagination in a web API :

  • Defining pagination parameters (page size, page number)
  • Retrieving data based on the pagination parameters
  • Including pagination metadata in the response (total items, number of pages, current page)
  • Providing customization options for sorting, filtering, and other parameters.

46. What exactly are webhooks?

Webhooks are real-time notifications sent by servers to specified URLs (callback URLs) when specific events occur. Unlike regular API calls initiated by clients, webhooks are server-initiated, asynchronous requests.

They work on the "fire and forget" principle, enabling the server to start the webhook without waiting for a response. They are commonly used in event-driven architectures; webhooks allow applications to respond to events without repeated polling.

47. What are the key considerations when designing a scalable web API? 

Key considerations when designing a scalable web API:

  • Horizontal scaling: Design API such that it handles increased traffic and load by adding more servers or instances.
  • Caching: use caching to store and serve frequently accessed data or responses and reduces load over API.
  • Asynchronous processing: It helps in running long operations without blocking the APIs.
  • Leveraging distributed systems: Design API to leverage distributed systems such as message queues or distributed databases, as this would improve scalability.

48. How to handle data validation in a web API? 

Key considerations when handling data validation in a web API:

  • Input and Data type validation to ensure they are of expected formats to prevent common security issues like XSS.
  • Error handling should be done by providing logical messages on validation failure. 
  • Use proper HTTP status codes to indicate the results of the validation process. For Example, “400 for Bad request”
  • Test API with various input scenarios, including edge cases and malicious inputs, to ensure the validation process works correctly.
  • Data validation should only occur after the authentication and authorization checks.

49. What are some best practices for testing web APIs?

Testing should cover every scenario. Below are some practices:

  • Test different HTTP methods (GET, POST, PUT, DELETE) to ensure proper handling of each request type.
  • Validate response status codes to ensure they align with the expected behaviour (e.g., 200 for success, 400 for client errors).
  • Perform performance testing to determine the API's responsiveness and scalability under various load conditions.
  • Perform security testing to identify flaws such as input validation issues, authentication flaws, or potential data leaks.
  • Test edge cases and boundary conditions to validate the API's behaviour in difficult scenarios,

50. How to monitor the performance and usage of a web API? 

By implementing logging and monitoring systems, tracking response times, error rates and usage patterns, one can monitor the performance and usage of web API. 
Some of the tools like Prometheus and Grafana for API monitoring services.

Frequently Asked Questions

What is the Web API method?

Web API methods typically refer to the HTTP methods used to interact with resources. Common HTTP methods include GET (retrieve data), POST (create data), PUT (update data), and DELETE (remove data). Web API methods determine how clients can interact with the API's resources.

What is the purpose of Web API?

The main purpose of a Web API is to provide communication between two software applications over the Internet. It also helps them to exchange information that developers can use in other applications while building it.

What are the 4 main types of Web APIs?

The four main types of Web APIs are REST(Representational State Transfer) APIs, SOAP(Simple object access protocol) APIs, GraphQL APIs, and RPC(Remote Procedure call) APIs. Each of these has its own strengths and weaknesses.

Who uses Web API?

Web APIs can be used by various types of developers, organizations, and industries. Web API can be used by web and mobile application developers, e-commerce companies, social media companies, financial institutions, etc.

What is web API also known as?

Web API is also known as a web service. It is also known as a web application programming interface. These terms are used interchangeably to refer to the same thing.


We’ve concluded our Web API interview questions. This article covered some of the most common interview experiences you might encounter during your Web API Interview Questions.

You can learn about the basics of Web API Interview Questions by visiting this link and understanding Web API usage.

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