40+ [REAL-TIME] Web API Interview Questions and Answers

Last updated on 18th Nov 2021, Blog, Interview Questions

Our Web API Interview Questions & Answers will not only help you deal with the toughest of the Web API interview questions, but also guide you in dealing with every technical question related individually, be it HTTP, ASP.NET Web API, Resources and URIs, WCF vs ASP.NET Web API etc. These 50+ Web API Interview Questions & Answers are created by the best in the business and help you in achieving your dreams of getting the Web API Developer job you have always aspired for.

1.Why is the Web API important?

Ans:

Web API is generally considered as a service that basically provides us information or data from the server. It is very important because of the following reasons:-

• It is used to provide an interface for websites and client applications to have access to data.
• It can also be used to access data from the database and save data back to the database.

2.What is Web API and why we use it ?

Ans:

Web API (Application Programming Interface), as the name suggests, is an API that can be accessed over the Web using the HTTP protocol. It is basically considered the best platform for revealing or uncovering data and services to various different services. It is a tool that can be used to push data to a server and can be accessed by server code. It can be built or developed using various technologies like java, ASP.NET, etc.

Web API Uses:
• It contains additional layers that simply standardize communications and provide different options on how to format input and output.
• It can be used with ASP.NET MVC and different types of web applications such as ASP.NET WebForms.

3.What are the main return types supported in Web API?

Ans:

It does not have any specific data type. It can return data of any type depending upon the business requirement. There are many HTTP methods like GET, POST, PUT, etc., which can return data in different formats depending upon the use case.

4.What is the difference between Web API and WCF?

Ans:

Web API	WCF
It is used to develop both SOAP-based services and RESTful services.	It is used to deploy only SOAP-based services.
It supports various MVC features such as routing, model binding, etc.	It does not support any MVC features.
It only supports HTTP protocol.	It supports various protocols such as HTTP, UDP, custom transport.
It is considered best for developing RESTFUL services.	It supports only limited RESTFUL services.
It is good when one wants to expose an expensive range of clients such as iPhones, browsers, mobile phones, tablets, etc.	It is good for creating services that uses expedite transport channels such as TCP, UDP, Named pipes, etc.
It offers support for UTF-8 encoding format.	It offers TEXT, Binary encoding support, MTOM (Message Transmission Optimization Mechanism), etc.

5.Why to choose Web API over WCF?

Ans:

Web API is considered the best choice over WCF because of the following reasons:-

• Web API uses all features of HTTP such as URIs, request/response headers, caching, versioning, various content formats, etc.
• One does not have to define or explain any extra config setting for different devices in Web API.

6.What is different between REST API and RESTful API?

Ans:

REST API	RESTful API
REST is an architectural pattern used for creating web services.	RESTful API is used to implement that pattern.
The data format of REST is based on HTTP.	The data format of RESTful is based on JSON, HTTP, and Text.
Working of URL is based on request and response.	Working of RESTful is based on REST applications.
It is required to develop APIs that allow interaction among clients and servers.	It simply follows REST infrastructure that provides interoperability among different systems on the whole network.
It is more user-friendly and highly adaptable to all business enterprises and IT.	It is too flexible.

7.What are the advantages of using Rest in Web API?

Ans:

REST is very important and beneficial in Web API because of the following reasons:-

• It allows less data transfer between client and server.
• It is easy to use and lightweight. It provides more flexibility.
• It also handles and controls various types of calls, returning various data formats.

8.What is REST and SOAP?

Ans:

REST and SOAP are 2 different approaches to online data transmission. Representational state transfer (REST) is a set of architectural principles. Simple object access protocol (SOAP) is an official protocol maintained by the World Wide Web Consortium (W3C).

9.What is Web API 2.0?

Ans:

It is basically an enhanced and modified feature of Web API. This new version supports various new features as given below:-

• New Routing Attribute.
• Secure ASP.NET Web API using OAuth 2.0.
• Support for Cross-Origin requests using CORS.
• IHttpActionResult return type.

10.Explain media type formatters.

Ans:

In web API, media type formatters are classes that are responsible for serialization data. Here, serialization generally means a process of translating data into a format that can be transmitted and reconstructed later. Because of serializing request/response data, Web API can understand request data format in a better way and send data in a format that the client expects. It simply specifies data that is being transferred among client and server in HTTP response or request.

11.What is Uri in API testing?

Ans:

A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. Each URI begins with a scheme name, as defined in Section 3.1, that refers to a specification for assigning identifiers within that scheme.

12.Which of the following Open-source libraries is used by WEB API for JSON serialization?

Ans:

Json.NET library is generally used by Web API for JSON serialization.

13.What is XML and JSON?

Ans:

XML (Extensible Markup Language):-

• It is especially designed to store and transport data.
• It is similar to HTML but is more flexible than HTML because it allows users to create their own custom tags.
• It is used for representing structured information such as documents, data, configuration, etc.
• JSON (JavaScript Object Notation):
• It is a lightweight format designed to store and transport data.
• It is easier to understand and is a standard text-based format used for representing structured data based on JavaScript object syntax.

14.What are Web API filters?

Ans:

Filters are basically used to add extra logic at different levels of Web API framework request processing. Different types of Web API filters are available as given below:

Authentication Filter: It handles authentication and authenticates HTTP requests. It also helps to authenticate user detail. It checks the identity of the user.

Authorization Filter: It handles authorization. It runs before controller action. This filter is used to check whether or not a user is authenticated. If the user is not authenticated, then it returns an HTTP status code 401 without invoking the action.

15.Who can consume Web API?

Ans:

A large range of clients such as browsers, mobile devices, iPhone, etc., include or consume web API. It is also good for using along native applications that require web services but not SOAP support. It can also be consumed by any client that supports HTTP verbs such as GET, DELETE, POST, PUT.

16.How to handle errors in Web API?

Ans:

Web API generally provides greater flexibility in terms of handling errors. Exception handling is a technique that is used to handle run-time errors in application code. One can use HttpResponseException, HttpError, Exception filters, register exception filters, Exception handlers to handle errors. Exception filter can be used to identify unhandled exceptions on actions or controllers, exception handlers can be used to identify any type of unhandled exception application-wide, and HttpResponseException can be used when there is the possibility of an exception.

17.How to register an exception filter globally?

Ans:

One can register exception filter globally using following code:-

• GlobalConfiguration.Configuration.Filters.Add (new
• MyTestCustomerStore.NotImplExceptionFilterAttribute

18.What is MVC?

Ans:

MVC (Model, View, and Controller) is basically an application design model that comprises three interconnect parts I.e., model, view, and controller. It allows coders to factor out different components of the application and update them more easily. It is mostly used for developing model user interfaces. Its main purpose is to display patterns in structure for keeping display and data separate to enable both of them to change without affecting others.

19.Write difference between MVC and Web API?

Ans:

MVC	Web API
It can be used to build Web applications that reply as both data and views.	It is used to build HTTP services that reply only as data.
It returns data in JSON format by using JSONResult.	It returns data in different formats such as JSON, XML, etc.
It supports content negotiation, self-hosting.	It does not support content negotiation, self-hosting.
It is not able to build REST-full services.	It is very helpful in creating REST-full services.
It returns a view (HTML).	It returns REST responses.

20.What is ASP.NET Web API?

Ans:

ASP stands for Active server pages. ASP.NET is an updated version of legacy ASP. It is a framework that is used for developing HTTP services to provide responses to client requests. It can be accessed in different applications on different platforms. It is provided by Microsoft open-source technology for developing and consuming HTTP-based services on top of .NET Framework. It is very easy to build HTTP services using ASP.NET Web API. These services can be used by different clients as given below:-

• Desktop Applications
• Mobile Applications
• IOTs
• Browsers

21.What are the advantages of using ASP.NET Web API?

Ans:

Some of the core advantages of using ASP.NET Web API are given below:-

• It provides the best platform for developing RESTful applications on .NET Framework.
• It works the same way that HTTP works with help of HTTP verbs such as GET, POST, PUT, DELETE for all crud operations.

22.What are new features used in ASP.NET Web API 2.0?

Ans:

ASP.NET Web API includes a number of new exciting features as given below:-

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

23.What is the use of Http Response Message?

Ans:

It is used to set response values such as header and status control. It simply allows us to work with HTTP protocol. It represents HTTP response messages that encapsulate data and status code.

24.What is the difference between ApiController and Controller?

Ans:

• ApiController: It is used to return data that is arranged in series and then sent to the client.
• Controller: It is used to provide normal views.

25.What do you mean by Caching?

Ans:

Caching is basically a technique or process of storing data somewhere or in the cache for future requests. The cache is a temporary storage area. Caching keeps all frequently or recently accessed files or data in the cache memory and accesses them from the cache itself rather than actual address of data or files. The cache interface simply improves the storage mechanism for request/response object pairs that are being cached.

26.What is the types of Caching

Ans:

There are basically three types of caching as given below:-

• Page Caching.
• Data Caching.
• Fragment Caching.

27.What is Advantages of Caching?

Ans:

• It is considered the best solution to ensure that data is served where it is needed to be served that too at a high level of efficiency which is best for both client and server.
• It delivers web objects faster to the end-user.
• It reduces load time on the website server.
• It leads to faster execution of any process.
• It decreases network costs.

28.WCF is replaced by ASP.NET Web API. True/False?

Ans:

WCF: It is a framework used for developing SOAP (Service Oriented Applications Protocols). It also supports various transport protocols as given above. ASP.NET Web API: It is a framework used for developing non-SOAP-based services. It is limited to HTTP-based services.

29.What are the main return types supported in ASP. Net Web API?

Ans:

It supports the following return types:-

• HttpResponseMessage.
• IHttpActionResult.
• Void.
• Other types such as string, int, etc.

30.Why rest APIs are stateless?

Ans:

Statelessness helps in scaling the APIs to millions of concurrent users by deploying it to multiple servers. Any server can handle any request because there is no session related dependency. Being stateless makes REST APIs less complex – by removing all server-side state synchronization logic.

31.How can ways to implement?

Ans:

Routing in Web API as given below:-

• Convention-based routing: Web API supports convention-based routing. In this type of routing, Web API uses route templates to select which controller and action method to execute.
• Attribute-based routing: Web API 2 generally supports a new type of routing known as attribute routing. As the name suggests, it uses attributes to define routes. It is the ability to add routes to the route table via attributes.

32.HOW to secure ASP.NET Web API?

Ans:

Web API has become key to programming web-based interactions. It can be accessed by anyone who knows the URL. Therefore, they have become targets for hackers. One needs to secure Web API by controlling Web API and by deciding who can and who cannot have access to Web API.

33.What is parameter in API?

Ans:

API parameters are the variable parts of a resource. They determine the type of action you want to take on the resource. Each parameter has a name, value type ad optional description. … In simple terms, API parameters are options that can be passed with the endpoint to influence the response.

34.What is HttpConfiguration in Web API?

Ans:

It is considered as the main class that includes different properties with help of which one can override the default behavior of Web API.

35.Can we return View from ASP.NET Web API method?

Ans:

No, we cannot return the view from the ASP.NET Web API method. ASP.NET web API develops HTTP services that provide raw data or information. ApiController in ASP.NET MVC application only renders data that is serialized and sent to the client. One can use a controller to provide normal views.

36.What is content negotiation in ASP.Net Web API?

Ans:

Content negotiation is basically a process of selecting the best representation from multiple representations that are available for a given response. It simply allows one to choose rather than negotiate content that one wants to get in response. It is performed at the server-side. In simple words, it chooses the best media type for matters to return a response to an incoming request.

37.Difference between HTTP GET vs HTTP Post?

Ans:

HTTP GET: This method is used to get information or data from a respective server at a specified URL. HTTP POST: This method is used to send data or information to respective servers.

38.What is HTTP?

Ans:

HTTP (HyperText Transfer Protocol) simply manages request-response between client and server. It works as a request-response protocol between client and server.

39.What is CORS in Web API?

Ans:

CORS (Cross-Origin Resource Sharing) is basically a mechanism that allows one to make requests from one website to another website in a browser that is normally not allowed by another policy called SOP (Same Origin Policy). It supports secure cross-origin requests and data transfers among clients or browsers and servers. Here, cross-origin request means requests coming from different origins. CORS simply resolves the same-origin restriction for JavaScript. One can enable CORS for web API using the respective web API package or OWIN middleware.

40.Name method that validates all controls on page?

Ans:

Page.Validate()

41.What parameters can be passed in the URL of API?

Ans:

Context keys, documents keys, or anything that initiates API to hit the exact end-point are few parameters that one can pass in the URL to define the complete end-point.

42.What is the use of DelegatingHandler?

Ans:

DelegatingHandler is used to develop a custom Server-Side HTTP Message Handler in ASP.NET Web API. It is used to represent Message Handlers before routing in Web API.

43.Web API uses which library for JSON serialization?

Ans:

Json.NET library is used by Web API for JSON serialization.

44.Explain method to handle error using HttpError in Web API?

Ans:

CreateErrorResponse is an extension method that can be used in Web API controller methods to return error codes and error messages. It creates an HttpError object and then wraps it inside an HttpResponseMessage object.

45.What is OData in Web API?

Ans:

The Open Data Protocol (OData) is a data access protocol for the web. OData provides a uniform way to query and manipulate data sets through CRUD operations (create, read, update, and delete). ASP.NET Web API supports both v3 and v4 of the protocol.

46.What is Web API?

Ans:

WebAPI is a framework which helps you to build/develop HTTP services.

47.Why is Web API required? Is it possible to use RESTful services using WCF?

Ans:

Yes, we can still develop RESTful services with WCF. However, there are two main reasons that prompt users to use Web API instead of RESTful services. Web API increases TDD (Test Data Driven) approach in the development of RESTful services.

48.Why select Web API?

Ans:

It is used to create simple, non-SOAP-based HTTP Services

It is also an easy method for creation with Web API. With WCF REST Services

It is based on HTTP and easy to define, expose and consume in a REST-ful way.

It is lightweight architecture and ideal for devices that have limited bandwidth like smartphones.

49.Is it right that ASP.NET Web API has replaced WCF?

Ans:

It’s a not at all true that ASP.NET Web API has replaced WCF. In fact, it is another way of building non-SOAP based services, i.e., plain XML or JSON string.

50.By default, Web API sends HTTP response with which of the following status code for all uncaught exception?

Ans:

500 – Internal Server Error.

51.What is the biggest disadvantage of “Other Return Types” in Web API?

Ans:

The biggest disadvantage of this approach is that you cannot directly return an error code like 404 error.

52.What is Web API Routing?

Ans:

Routing is pattern matching like in MVC.

53.What is SOAP?

Ans:

SOAP is an XML message format used in web service interactions. It allows to send messages over HTTP or JMS, but other transport protocols can be used. It is also an XML-based messaging protocol for exchanging information among computers.

54.What is the benefit of using REST in Web API?

Ans:

REST is used to make fewer data transfers between client and server which make it an ideal for using it in mobile apps. Web API also supports HTTP protocol. Therefore, it reintroduces the traditional way of the HTTP verbs for communication.

55.What is the most widely used web service API?

Ans:

REST accounts for more than 80% of all API types used for web services, making it the most widely used web service API.

56.How to you can limit Access to Web API to Specific HTTP Verb?

Ans:

Attribute programming plays a important role. It is easy to restrict access to an ASP.NET Web API method to be called using a particular HTTP method.

57.Can you use Web API with ASP.NET Web Form?

Ans:

Yes, It is possible to use Web API with ASP.Net web form. As it is bundled with ASP.NET MVC framework. However, it can be used with ASP.NET Web Form.

58.How Can assign alias name for ASP.NET Web API Action?

Ans:

We can give alias name for Web API action same as in case of ASP.NET MVC by using “ActionName” attribute as follows:

• [HttpPost]
• [ActionName(“SaveStudentInfo”)]
• public void UpdateStudent(Student aStudent)
• {
• StudentRepository.AddStudent(aStudent);
• }

59.What is the meaning of TestApi?

Ans:

TestApi is a utility library of APIs. Using this library tester developer can create testing tools and automated tests for a .NET application using data-structure and algorithms.

60.Explain exception filters?

Ans:

It will be executed when exceptions are unhandled and thrown from a controller method. The reason for the exception can be anything. Exception filters will implement “IExceptionFilter” interface.

61.How you can return View from ASP.NET Web API method?

Ans:

No, we can’t return a view from ASP.NET Web API Method. Web API creates HTTP services that render raw data. However, it’s also possible in ASP.NET MVC application.

62.How to register exception filter globally?

Ans:

It is possible to register exception filter globally using following code-

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

63.Explain what is REST and RESTFUL?

Ans:

REST represents REpresentational State Transfer; it is entirely a new aspect of writing a web app.RESTFUL: It is term written by applying REST architectural concepts is called RESTful services. It focuses on system resources and how the state of the resource should be transported over HTTP protocol.

64.Give me one example of Web API Routing?

Ans:

65.How can you handle errors in Web API?

Ans:

Several classes are available in Web API to handle errors. They are HttpError, Exception Filters, HttpResponseException, and Registering Exception Filters.

66.What New Features comes with ASP.NET Web API 2.0?

Ans:

The latest features of ASP.NET Web API framework v2.0 are as follows:

• Attribute Routing
• Cross-Origin Resource Sharing
• External Authentication
• Open Web Interface NET
• HttpActionResult
• Web API OData

67.How can you restrict access methods to specific HTTP verbs in Web API?

Ans:

With the help of Attributes (like HTTP verbs), It is possible to implement access restrictions in Web API.It is possible to define HTTP verbs as an attribute to restrict access.

68.How can you pass multiple complex types in Web API?

Ans:

Two methods to pass the complex types in Web API – Using ArrayList and Newtonsoft array

69.Write a code for passing ArrayList in Web API?

Ans:

70.Name the tools or API for developing or testing web api?

Ans:

Testing tools for web services for REST APIs include:-

• Jersey API
• CFX
• Axis
• Restlet

71.What is REST?

Ans:

REST is architectural style. It has defined guidelines for creating services which are scalable. REST used with HTTP protocol using its verbs GET, PUT, POST and DELETE.

72.What is rest in web?

Ans:

Representational State Transfer (REST) is an architectural style that specifies constraints, such as the uniform interface, that if applied to a web service induce desirable properties, such as performance, scalability, and modifiability, that enable services to work best on the Web.

73.How can we restrict access to methods with specific HTTP verbs in Web API?

Ans:

Attribute programming is widely used for this functionality. Web API also allows restricting access of calling methods with the help of specific HTTP verbs. It is also possible to define HTTP verbs as attribute over method.

74.What is the usage of DelegatingHandler?

Ans:

DelegatingHandler is used in the Web API to represent Message Handlers before routing.

75.How can we register exception filter from the action?

Ans:

76.Tell me the code snippet to show how we can return 404 errors from HttpError?

Ans:

Code for returning 404 error from HttpError string message = string.Format(“TestCustomer id = {0} not found”, customerid); return Request.CreateErrorResponse(HttpStatusCode.NotFound, message);

77.Explain code snippet to register exception filters from controller?

Ans:

[NotImplExceptionFilter]

public class TestCustController : Controller

{

//Your code goes here

}

78.Web API supports which protocol?

Ans:

Web App support HTTP protocol

79.Which of the following .NET framework supports Web API?

Ans:

Web API is supported by NET 4.0 version

80.What is endpoint in API?

Ans:

Simply put, an endpoint is one end of a communication channel. When an API interacts with another system, the touchpoints of this communication are considered endpoints. For APIs, an endpoint can include a URL of a server or service. The place that APIs send requests and where the resource lives, is called an endpoint.

81.Explain method to handle error using HttpError in Web API?

Ans:

In WEB API HttpError used to throw the error info in the response body. “CreateErrorResponse” method is can also use along with this, which is an extension method defined in “HttpRequestMessageExtension.”

82.How to handle errors in Web API?

Ans:

Several classes are available in Web API to handle errors. They are HttpError, HttpResponseException, Exception Filters, Registering Exception Filters.

83.What is the benefit of WebAPI over WCF?

Ans:

WCF services use the SOAP protocol while HTTP never use SOAP protocol. That’s why WebAPI services are lightweight since SOAP is not used. It also reduces the data which is transferred to resume service. Moreover, it never needs too much configuration. Therefore, the client can interact with the service by using the HTTP verbs.

84.State differences between MVC and WebAPI.

Ans:

MVC framework is used for developing applications which have User Interface. For that, views can be used for building a user interface. WebAPI is used for developing HTTP services. Other apps can also be called the WebAPI methods to fetch that data.

85.Who can consume WebAPI?

Ans:

WebAPI can be consumed by any client which supports HTTP verbs such as GET, PUT, DELETE, POST. As WebAPI services don’t need any configuration, they are very easy to consume by any client. Infract, even portable devices like Mobile devices can easily consume WebAPI which is certainly the biggest advantages of this technology.

86.How can we make sure that Web API returns JSON data only?

Ans:

To make Web API serialize the returning object to JSON format and returns JSON data only. For that you should add the following code in WebApiConfig.cs class in any MVC Web API Project:

• //JsonFormatter
• //MediaTypeHeaderValue
• Config.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue(“application/json”));
• //JsonFormatter
• //MediaTypeHeaderValue
• Config.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue(“application/json”))

87.What is ASP.Net?

Ans:

It is a framework developed by Microsoft on which we can develop new generation web sites using web forms(aspx), MVC, HTML, Javascript, CSS etc. Its successor of Microsoft Active Server Pages(ASP). Currently there is ASP.NET 4.0, which is used to develop web sites. There are various page extensions provided by Microsoft that are being used for web site development. Eg: aspx, asmx, ascx, ashx, cs, vb, html, XML etc.

88.What’s the use of Response.Output.Write()?

Ans:

We can write formatted output using Response.Output.Write().

89.In which event of page cycle is the ViewState available?

Ans:

After the Init() and before the Page_Load().

90.What is the difference between Server.Transfer and Response.Redirect?

Ans:

In Server.Transfer page processing transfers from one page to the other page without making a round-trip back to the client’s browser. This provides a faster response with a little less overhead on the server. The clients url history list or current url Server does not update in case of Server.Transfer.Response.Redirect is used to redirect the user’s browser to another page or site. It performs trip back to the client where the client’s browser is redirected to the new page. The user’s browser history list is updated to reflect the new address.

91.Which validator control you use if you need to make sure the values in two different controls matched?

Ans:

Compare Validator control.

92.What is ViewState?

Ans:

ViewState is used to retain the state of server-side objects between page post backs.

93.Where the viewstate is stored after the page postback?

Ans:

ViewState is stored in a hidden field on the page at client side. ViewState is transported to the client and back to the server, and is not stored on the server or any other external source.

94.How long the items in ViewState exists?

Ans:

They exist for the life of the current page.

95.What is Protected Configuration?

Ans:

It is a feature used to secure connection string information.

96.How can we prevent browser from caching an ASPX page?

Ans:

We can SetNoStore on HttpCachePolicy object exposed by the Response object’s Cache property:-

Response.Cache.SetNoStore (); Response.Write (DateTime.Now.ToLongTimeString ());

97.What is the good practice to implement validations in aspx page?

Ans:

Client-side validation is the best way to validate data of a web page. It reduces the network traffic and saves server resources.

98.Explain role based security ?

Ans:

Role Based Security used to implement security based on roles assigned to user groups in the organization.

99.What is Cross Page Posting?

Ans:

When we click submit button on a web page, the page post the data to the same page. The technique in which we post the data to different pages is called Cross Page posting. This can be achieved by setting POSTBACKURL property of the button that causes the postback. Findcontrol method of PreviousPage can be used to get the posted values on the page to which the page has been posted.

100.What is RedirectPermanent in ASP.Net?

Ans:

RedirectPermanent Performs a permanent redirection from the requested URL to the specified URL. Once the redirection is done, it also returns 301 Moved Permanently responses.