Top 18 Web API Basic Interview Questions to Know in 2024-2025

Introduction

Have you ever wondered how websites seamlessly exchange data with servers? This magic happens thanks to Web APIs, the backbone of modern web applications. Web APIs, or Application Programming Interfaces, are not a recent innovation but have evolved significantly since their inception. In the early 2000s, they made waves marking pivotal moments in e-commerce history. 

On February 7, 2000, Salesforce introduced the concept of a Web API at the IDG Demo 2000 conference, setting the stage for future developments. Later that year, on November 20, eBay followed suit with its API, launching the eBay Developers Program. The trend continued with Amazon unveiling its web services on July 16, 2002, empowering developers to integrate Amazon's extensive features into their websites.

Originally, Web APIs were a niche interest in the tech community, primarily utilized by early e-commerce pioneers. However, they have since become indispensable tools for mainstream businesses. Today, Web APIs enable seamless data exchange and service integration across diverse platforms, ranging from mobile to complex web applications. Their flexibility, efficiency, and compatibility with various devices and browsers make them a cornerstone of contemporary web development, driving innovation and enhancing user experiences globally.

List of Web API Interview Questions

1. Why is the Web API important?

Web API is crucial because it provides an interface for websites and client applications to access data. It can interact with databases to retrieve and save data and supports various text formats such as XML and JSON. It is compatible with any browser and device, uses low bandwidth, enhances UI/UX, increases interest in a company's products and services, and boosts website traffic.

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

The HTTP protocol can access web API (Application Programming Interface). It reveals data and services to various platforms and can be developed using technologies like Java and ASP.NET. It standardizes communications, works with ASP.NET MVC and web applications, and is ideal for creating resource-oriented and RESTful services.

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

Web API does not have specific data types. Depending on the business requirements, it can return data in various formats like XML and JSON through different HTTP methods (GET, POST, PUT, etc.).

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

WCF (Windows Communication Foundation) is a framework for developing SOAP-based services, whereas Web API is for developing both SOAP and RESTful services. Web API supports HTTP protocol, is best for RESTful services, and is ideal for exposing services to a wide range of clients. WCF supports multiple protocols and is suitable for services requiring rapid transport channels.

5. Why choose Web API over WCF?

Web API is preferred over WCF because it utilizes HTTP features, supports various text formats, is faster for lightweight services, supports MVC features, provides more flexibility, and uses standard security measures like token and basic authentication.

6. What is the difference between REST API and RESTful API?

REST (Representation State Transfer) is an architectural style for creating web services, while RESTful API implements that pattern. REST works with HTTP, and RESTful API uses formats like JSON and HTTP. REST is user-friendly and adaptable, while RESTful API ensures interoperability among different systems.

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

REST is beneficial because it allows less data transfer, is lightweight, provides flexibility, handles various calls and data formats, and is ideal for mobile apps. It uses simple HTTP calls, making it easier to implement than complex options like CORBA or SOAP.

8. What are REST and SOAP, and how do they differ?

REST is an architectural pattern for web services using formats like JSON and XML, while SOAP (Simple Object Access Protocol) is a protocol for exchanging structured information using XML. REST is stateless, faster, and simpler, while SOAP includes built-in error handling and uses WSDL for communication.

9. What is Web API 2.0?

Web API 2.0 is an enhanced version with features like new routing attributes, OAuth 2.0 security, support for Cross-Origin requests using CORS, IHttpActionResult return type, and support for $expand and $select in OData Service. These features make it optimal for developing RESTful services on various platforms.

10. Explain media type for matters in Web API?

Media type formatters are classes responsible for data serialization, translating data into a format that can be transmitted and reconstructed. They specify data formats transferred between client and server. Examples include JsonMediaTypeFormatter for JSON and XmlMediaTypeFormatter for XML.

11. Which protocol does Web API support?

Web API supports only the HTTP protocol.

12. Web API uses which open-source library for JSON serialization?

Web API uses the Json.NET library for JSON serialization.

13. What are XML and JSON?

• XML (Extensible Markup Language) is designed to store and transport data. It allows users to create custom tags and represents structured information.
• JSON (JavaScript Object Notation) is a lightweight format for storing and transporting data. Based on JavaScript object syntax, it is easier to understand and faster to use.

14. What are Web API filters?

Filters add extra logic at different levels of request processing in Web API. Types include Authentication Filter (handles authentication), Authorization Filter (checks user authorization), Action Filter (adds logic before/after controller actions), Exception Filter (handles unhandled exceptions), and Override Filter (modifies the behavior of other filters).

15. Who can consume Web API?

Web API can be consumed by a wide range of clients, such as browsers, mobile devices, and native applications that require web services but not SOAP support. Any client supporting HTTP verbs (GET, DELETE, POST, PUT) can use it.

16. How to handle errors in Web API?

Web API provides flexibility in handling errors through techniques like HttpResponseException, HttpError, Exception filters, and Exception handlers. These tools help identify and manage unhandled exceptions at different levels.

17. How do you register an exception filter globally?

You can register an exception filter globally using the following code: GlobalConfiguration.Configuration.Filters.Add(new MyTestCustomerStore.NotImplExceptionFilterAttribute());

18. What is MVC, and how does it differ from Web API?

MVC (Model, View, and Controller) is an application design model for developing user interfaces. It allows separate updating of display and data components.

• MVC: Builds web applications that return data and views, supports content negotiation and self-hosting, and is unsuitable for building RESTful services.
• Web API: Builds HTTP services that return data only, supports different data formats, and is ideal for creating RESTful services.

Also read: NET core Interview Questions

Conclusion

Web APIs are crucial for modern web development, enabling efficient data exchange and service integration across various platforms. Understanding the basic concepts, differences between Web API and other frameworks like WCF, and the advantages of using REST can help you excel in Web API-related roles. Familiarity with common interview questions and their answers can significantly enhance your preparation for interviews in 2024-2025.