50 Top Web API Interview Questions and Answers for 2024

Web API is an application programming interface allowing web services to be available to browsers and devices, such as tablets, mobile, etc. It was first introduced in February 2000 by Salesforce. Since then, Web API has gained massive popularity due to its lightweight, simple services and stand-alone web services application.

Whether you are a beginner or experienced IT professional trying to enter into the developing field, you must know the importance of having a robust resource for cracking your upcoming interviews.

With the changing technology, the Web API field is also evolving. If you are planning to apply to any Web API positions, take a look at these web API interview questions to prepare!

Web API Interview Questions and Answers

The following are some of the most commonly asked Web API interview questions, categorized into three levels: beginner, intermediate, and advanced

Web API Interview Questions for Beginners

1. Why is Web API important?

Web API is a service that provides you with the information or data from the server. It is essential for business growth. Here are a few reasons why Web API is important:

• Offers an interface for both websites and the client applications to access the data
• Supports various text formats, such as XML and JSON, etc.
• Works well on devices with low bandwidth
• Commonly used for creating UI/UX, resulting in increased traffic to the website
• Compatible with any type of browser and device

2. What are the business benefits of Web API?

Here are some of the business benefits of Web API:

• Reduces manual effort by centralizing business logic, maintaining business information with efficiency and consistency
• Ability to access Web APIs via several HTTP clients, such as Windows (7, 8), Android, iPad, etc.
• Open-source
• Has a similar controller pattern to the MVC controller, making it easy to understand
• Part of the Asp.net framework, meaning there is no dependency on development and deployment.

3. What are the technical benefits of Web API?

Web API has a few technical benefits:

• Easy configuration
• Separate from UI development
• Simple business logic testing with advanced tools such as rest-client
• Lightweight architecture, suitable for devices with low bandwidth
• Based on HTTP, making it easier to define
• Supported by many MVC features, like action results, model binders, etc.
• Comes with descriptive message headers that determine the content type, and headers that explain how to secure it, cache information, etc.
• Performs standard CRUD (Create Read Update Delete) operations via the HTTP forms, such as GET, PUT, POST, and DELETE
• Enables you to develop full-featured REST services
• API service interface consists of URL patterns and HTTP methods
• Helps you access non-SOAP-based services, such as XML or JSON strings

4. What are the disadvantages of Web API?

Here are some disadvantages of Web API:

• Web API incurs costs in terms of development time and maintenance.
• Web API makes your website vulnerable to cyber attacks.
• API usage isn’t always predictable.
• You need to have the technical knowledge to construct APIs.
• The API can crash while testing, resulting in increased maintenance costs.

5. Explain the difference between the Web API and WCF.

WCF is a framework for creating a distributed and interoperable application. It is also suitable for building service-oriented connected applications to transmit asynchronous data from one service point to another.

Web API is an interface for web browsers and web servers. Browser API simply extends the functionality of web browsers, whereas Server API simply extends the functionality of web servers.

6. Why choose Web API over WCF?

Here are a few reasons why you should choose Web API over WCF:

• Web API comes with HTTP features, such as URIs, and supports various content formats, versioning, etc.
• You do not have to define different settings for supporting different devices.
• Due to the usage of XML, Web API is faster and more suitable for lightweight services.
• Web API is more flexible.
• It ensures security via token authentication and other methods.

7. What’s the difference between REST API and RESTful API?

REST API stands for Representational State Transfer API and follows rules for establishing communication between an application and services.

RESTful API is an Application Programming Interface(API) based on the REST architecture and interacts using RESTful web services.

The following table highlights the differences between REST API and RESTful API:

8. Why use REST in Web APIs?

You might use REST in Web APIs for a few reasons:

• Easier to understand
• Reduces application complexities and converts them into easy-to-use resources
• Capable of handling high loads using HTTP proxy and cache
• Helps new clients work on others’ applications, irrespective of their purpose
• Uses standard HTTP procedure call-outs to access data.
• REST API depends on codes, allowing you to easily synchronize data across the websites without complications.
• Follows a flexible approach and serializes the JSON or XML format data.
• The standards-based security uses OAuth protocol to verify each REST request.

9. State the difference between SOAP and REST.

REST (Representational State Transfer): An advanced form of web service describing the architectural style of networked systems. It does not require larger bandwidth to send the request to the server.

SOAP (Simple Object Access Protocol): A lightweight protocol used for exchanging structured and typed information on the Web. It is suitable for HTTP and RPC (Remote Procedure Call) and B2B applications. SOAP messages contain heavy data and require greater bandwidth.

10. What are media type formatters?

Media type formatters are classes responsible for serialization data. Serialization involves translating data into a format that is easy to transmit and reconstruct later.

With serializing request/response data, Web API can efficiently understand the request data format and send data in a format expected by the client. It specifies data exchanged between the client and the server in an HTTP response or request.

11. Which protocol is supported by Web API?

Web API supports the HTTP protocol.

12. What are JSON and XML?

XML (Extensible Markup Language) is designed for storing and transferring data in a structured format. It works similarly to HTML but is more flexible as the users can create their custom tags.

On the other hand, JSON (JavaScript Object Notation) is a lightweight format for storing and transferring data. It has text-based formatting for representing the structured data, making it easier to understand and faster to use.

13. What are different filters available in Web API?

Filters allow you to add extra logic at different levels of the Web API framework. The following are the different filters in Web API:

• Authentication filter: This filter takes care of the authentication and authorization HTTP requests. For example, checking the identity of the users.
• Authorization filter: This filter checks user authenticity and invokes the HTTP status code 401 if the user isn’t authenticated.
• AuthorizeAttribute: This is a built-in authorization filter.
• Action filter: You can apply this filter to controller action or the entire controller. You can use it to add the logic before or after the execution of the controller action.
• Exception filter: Handles all the unhandled exceptions thrown by controller actions in Web API.
• Override filter: Excludes specific action methods from the global filters, and helps modify the behavior of other filters.

14. Who uses Web API?

Browsers and mobile devices generally consume Web API. You can also use it for native applications that require web services. Finally, clients using HTTP verbs can use it.

Web API Interview Questions and Answers for Experienced Candidates (Intermediate)

15. Explain error handling in Web API.

Web API offers various error handling classes:

• HttpResponseException: Returns the HTTP status code mentioned in the exception Constructor.
• HttpError: Returns the meaningful error code to the client using the HttpResponseMessage.
• Exception filters: Caches the unhandled exceptions or errors generated in Web API and are useful when the controller action method throws the unhandled error.

16. Explain MVC and how it’s different from Web API.

MVC stands for Model, View, and Controller. Developers generally use it for developing model user interfaces. MVC keeps the data and the display separate and enables the developers to modify both without impacting each other.

The following points describe how MVC and Web API differ:

• MVC is commonly used for developing applications that return both data and views. On the other hand, Web API generates HTTP services effortlessly that returns only data, and not view.
• MVC uses action names to perform the tracing. Web API uses the HTTP services actions to perform the tracing.
• The Web API returns the information in JSON, XML, and other formats. MVC returns the data in JSON format only.
• Web API supports self-hosting and negotiation, while MVC does not.
• The Web API helps create the RESTful services using the .Net Framework, while MVC does not support it.

17. How can you host Web API?

You can host Web API using self-hosting and IIS hosting.

ASP.NET Web API Interview Questions

18. What is ASP.NET Web API?

ASP.NET Web API is a framework and a perfect solution for developing RESTful applications on the .NET framework. Using the ASP.NET Web API framework, you can seamlessly create HTTP services to respond to a broad range of clients, including browsers and mobile devices.

Microsoft provides this framework for developing HTTP-based services on top of the .Net framework.

19. What are the advantages of ASP.NET Web API?

Here are some advantages of ASP.NET Web API:

• Well-suited for creating RESTful applications on the .NET framework.
• Works similarly to the HTTP using GET, POST, PUT, DELETE for performing CRUD actions.
• A flexible option for creating Web API.
• Supports routing.
• Supports model binding, validation, Odata, etc.
• Uses ApiExplorer for developing custom help and test pages.
• Can seamlessly create non-SOAP-based services, such as XML, JSON, etc.

20. What is caching? What are a few different types of caching?

Caching involves temporarily storing information for quick reference. It contains all the frequently accessed files in its memory. Whenever you re-access those files, the cache memory shows you the files, rather than leading you to the actual website again and again.

A few different types of caching include:

• Page caching
• Fragment caching
• Data caching

21. Explain content negotiation in Web API.

Content negotiation refers to the method of selecting the best possible representation for a specific response. There are two types of headers available for content negotiation:

• Content-Type: This header tells the server about the information that it will receive from the client.
• Accept: This header shows the data format requested by the client from the server.

22. Explain ASP.NET Web API routing.

Routing is the process of matching the URI to an action using Web API. It helps in deciding which action and controller to call. The controller is a class handling the HTTP requests and this class comes with public methods known as action methods.

Routing is implemented in two different ways:

• Convention-based routing: This type of routing uses route templates for selecting the controller and execution method.
• Attribute-based routing: This type of advanced routing is supported by Web API 2. It uses attributes for defining and adding routes to the route tables.

23. How can you secure ASP.NET Web API?

Web API is known to program web-based interactions. Anyone can access these applications via URL, making them exposed to hackers. So, it’s important to secure the Web API and limit its access only to authorized users.

Here are two methods to make Web API more secure:

• Authentication: This method checks the user by confirming their username and password. If the details aren’t accurate, the server returns a 401 HTTP status code, specifying unauthorized access. To eliminate this error, you can use OAuth 2.0.
• Authorization: This measure confirms that a user has the appropriate access to perform certain actions.

24. What return types are supported by ASP.NET?

The supported return types are:

• HttpResponseMessage
• HttpActionResult,
• Void,
• String
• Int
• etc.

25. Explain exception filters in ASP.NET Web API.

This exception filter is used to handle all unexpected exceptions raised by Web API. This filter class implements the IExceptionFilters interface. This filter is executed whenever the controller throws an unexpected exception.

26. Explain CORS in Web API.

CORS stands for Cross-Origin Resource Sharing and allows users to make requests from one website to another within a browser. It handles cross-origin requests and data transmission from various origins. It seamlessly eliminates the limitations of the same-origin for JavaScript. You can enable CORS for Web API using web API packages.

27. How can you unit test Web API?

One of the commonly used unit testing tools for Web API is Fiddler. It is a free debugging proxy available for any browser to compose and execute several HTTP requests and check their response. It also tests RESTful web services efficiently.

On the Fiddler tool, you can follow the following steps to unit test:

Fiddler – Compose Tab -> Enter Request Headers -> Enter Request Body and then execute.

28. Explain how DelegatingHandler works.

DelegatingHandler develops a custom Server-Side HTTP Message Handler within the ASP.NET Web API. It is used to represent Message Handlers before it routes the message in Web API.

29. Which method validates all the controls on a page?

The Page.Validate() method validates all controls on a page.

30. Can a view be returned from the ASP.NET Web API method?

No, a view cannot be returned from the ASP.NET Web API method. The web API creates HTTP services to provide information. The ApiController in ASP.NET MVC application only renders the serialized data and sends it to the client. You can use a controller to provide normal views.

31. Which method handles error codes in Web API?

CreateErrorResponse is an extension method that returns error codes and error messages. It will create an HttpError object and wrap it inside an HttpResponseMessage object.

32. State the difference between HTTP GET and HTTP POST.

The following are the major differences between HTTP GET and HTTP POST methods:

Advanced-Level Interview Questions on Web API

33. What is an ApiController?

An ApiController returns the data in serial and then sends that data to the client. For example:

public class TBController : ApiController
{
// GET: /Api/TB/
public List<Tweet> Get()
{
return Twitter.GetTweets();
}
}

34. What is a controller?

You can use a controller to provide normal views:

public class TBController : Controller
{
// GET: /Tweets/ [HttpGet] public ActionResult Index()
{
return Json(Twitter.GetTweets(), JsonRequestBehavior.AllowGet);
}
}

35. What are the features of ASP.NET Web API 2.0?

The following are features of ASP.NET Web API 2.0:

• Attribute Routing
• CORS (Cross-Origin Resource Sharing)
• OWIN (Open Web Interface for .NET) self-hosting
• IHttpActionResult
• Web API OData

36. What are the different ways to conduct Web API versioning?

The following are the different ways to conduct Web API versioning:

• URI
• Query String Parameter
• Custom Header Parameter
• Accept Header Parameter

37. How do you register an exception filter globally?

You can use the following code to register an exception filter globally:

GlobalConfiguration.Configuration.Filters.Add (new MyTestCustomerStore.NotImplExceptionFilterAttribute());

38. What is TestAPI?

TestAPI is a utility library of APIs that helps developers create testing tools and automated tests for .Net applications.

39. How can you ensure that Web API returns data in JSON format only?

You need to open “WebApiConfig.cs” file and add the following line:

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

40. Can we use Web API 2 in a C# console application?

Yes, you can use Web API 2 in Console Application, MVC, Angular JS, or any other application.

41. How can you enable HTTPS in Web API?

ASP.Net Web API runs over HTTPS protocol. You can create a new class and get a class with AuthorizationFilterAttribute and check if the requested URL has HTTPS.

42. Explain token-based authentication.

Token-based authentication is a safe authentication process where users are authenticated with a signed token.

43. Explain the different HTTP methods.

There are 8 different HTTP methods:

• GET: Retrieves data from the respective server using a specific URI.
• HEAD: Similar to GET, but sends the status line and header section only.
• PUT: Updates and replaces all existing resources with the uploaded content.
• POST: Send data to the respective server.
• DELETE: Remove all current resources given by a URI.
• OPTIONS: Specifies communication options for the target resource.
• CONNECT: Creates a tunnel to the server based on a given URI.
• TRACE: Performs a message loop-back test along the path to the target resource.

44. What is an HTTP header?

An HTTP header allows the client and server to transmit additional information via the HTTP request and HTTP response. It is an integral part of both HTTP requests and responses. In other terms, we can define an HTTP header as code that transfers data between a web server and a client.

45. What .NET framework supports ASP.NET Web API?

The first version of ASP.NET Web API is introduced in .NET Framework 4. After that, all .NET Framework versions come with ASP.NET Web API support.

46. Describe the page life cycle.

During the execution of any ASP.Net page, several events take place even before the initialization of the page till its rendering. The events take place in chronological order, as shown below:

47. Which file helps with customizing the ASP.Net application?

To customize the ASP.net application, you can make the required changes to the web.config file.

48. What are web services?

These are software services that serve from one machine to another over the network. These services use XML and provide SSL and WSS for data transmission.

49. What is a session object?

A session object is an object storing necessary information about a user’s session. Standard information includes name, id, preferences, setting changes, etc. Session Object is initialized with the start of the session and is destroyed when the session expires.

50. Do web services support data readers like the POM object?

Yes, web services support data reader objects because they include business logic. As a result, we can use the data reader objects, like POM, in web services.

.NET/ C# Interview Masterclass - Top 500 Questions & Answers

Tips to Ace Web API Interviews

Now that you have a great resource of commonly asked Web API interview questions, you can easily ace your Web API interview. But, here are some helpful tips to increase your chances for success even further!

Prepare for scenario-based questions. An interviewer may ask you to describe situations where you used Web API. Think of a few successful stories before the interview date.

Communication skills. Proper communication is vital to ace an interview. Make eye contact, speak clearly, and make sure you add context to your answers where necessary.

Ask questions. At the end of the interview, you’ll be asked: “Do you have any questions for me?” Always think of a couple in advance to demonstrate your interest in the role and company.

Be confident. Easier said than done, we know! But preparation makes all the difference when it comes to confidence. Review your resume and achievements for a couple of days before your interview, and test out this article’s interview questions with a friend!

Learn from previous interviews. Did you have an interview where you remember stumbling over a particular question? Write that question down or any others like it and practice answering it before this interview.

Conclusion

Web API is commonly used within all web-based applications for effective and secure data transfer. If you want to be a successful web developer, you must understand the basics and advanced features of Web API, their latest versions in the market, how they work, and more.

We hope that this blog post has helped you get aware of commonly asked web API questions in interviews. We have covered frequently asked interview questions on Web API that help you polish your knowledge and ace your next Web API interview.

Interested in expanding your knowledge? Check out our article about API testing.

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