REST APIs (Representational State Transfer) are essential to modern web development. They allow different software applications to communicate over the internet using standard HTTP methods like GET, POST, PUT, and DELETE. If you’re just starting your career in tech, understanding how REST APIs work is a must. Interviewers often test your grasp of endpoints, status codes, request/response formats, and RESTful principles.
This guide compiles commonly asked REST API interview questions and answers to help you build a solid foundation. Whether you’re applying for a junior developer, QA, or support engineer role, these questions will help you explain core concepts clearly and confidently. REST APIs are used in everything from websites to mobile apps, so knowing them boosts your value across industries. Use this guide to brush up on basics and get ready to impress in your next tech interview.
Answer: Below are some benefits of statelessness in RESTful webservices:
- Web services can individually treat every method request.
- Web services don’t need to maintain a client’s previous interactions that simplify application design.
- As HTTP is a statelessness protocol, RESTful Web services seamlessly work with the HTTP protocol.
Answer: Web services need to gather & interpret extra information in each request to take care of the client’s interactions & avail the client state, which is the biggest disadvantage of statelessness in RESTful Webservices.
Answer: A few HTTP methods like GET that produces the same response regardless of how many times you use them. For instance, if you send multiple GET requests to the same URI, it will result in the same response without any side-effect, which is called idempotent.
Answer: Caching is the process wherein a server response is stored so a cached copy can be used when needed, and there is no need for generating the same response again. This process reduces the server load & increases the performance & scalability of the server. Only the client can cache the response for a limited period.
Answer: A web service enables communication amongst multiple applications by using open standards; WSDL, XML, HTML, & SOAP. A web service avails XML to tag data, SOAP to transfer the message, & WSDL to describe a service’s availability. You can build a Java-based web service on Solaris accessible from your Visual Basic program that runs on Windows. You can also utilize C# to develop new web services on Windows that can be invoked from web applications based on Java Server Pages (JSP) and run-on Linux.
Answer: These are some perks of web services:
- Interoperability: Through web services, an application can communicate with another application written in any language.
- Reusability: We can expose web services so that other applications can use them.
- Modularity: It allows you to build a service for a certain task like tax calculation.
- A standard protocol for each application program: Web services use a standard protocol so all the client apps written in different languages can understand it. It helps in obtaining cross-platform compatibility.
- Cheaper communication cost: Web services use SOAP over HTTP so anyone can deploy existing internet for using the web services.
Answer: There are two types of web services:
- SOAP Web Services: It runs on a SOAP protocol that uses XML for sending data.
- Restful Web Services: It is an architectural style that mostly runs on an HTTP protocol. REST is a stateless, client-server architecture wherein web services are resources & can be identified by their URIs. Client apps can utilize HTTP GET/POST methods to invoke the Restful web services.
Answer: WSDL or Web Services Description Language is an XML document containing web services information like method name, method parameter, port types, binding, service endpoint, etc. WSDL bridges the gap & provides the necessary information to the client. Some important elements used in WSDL are as follows:
- < message >: It is used to define various data elements for each operation performed by the web service.
- < portType >: It is used to determine operations performed by the web service. The operations can have two messages, including an input and an output message.
- < binding >: It contains the used protocol.
Answer: UDDI means Universal Description, Discovery & Integration. It is an XML-based framework for integrating, discovering and describing, web services. It has a list of available web services & WSDL is also a part of UDDI.
Answer: The following tools are used to test web services:
- SoapUI toolfor testing RESTful & SOAP web services
- Posterfor Firefox browser
- Postmanextension for Chrome
Answer: Today, most organizations worldwide have their enterprise systems containing different applications built around different platforms & technologies. As per a survey conducted by ZapThink approx 70% of IT companies’ spending budget revolves around maintaining & integrating these systems. Thus, integration solutions act as a significant business opportunity for services vendors & IT software companies. Interoperability is the core of any solution that addresses the integration problem in enterprise systems. Just like a seamless integration drives the web services development, interoperability drives the integration. In simple terms, interoperability means the suitability & capability of any system to be accessed & implemented in a platform-neutral & language-neutral manner. The standards define the modes in which a system may receive/send response/request to/from other systems, even if they are based on a different technology & platform domain.
Answer: Synchronicity refers to binding a client to the service execution. In synchronous invocations, the client blocks & waits for the service to finish its operation before executing other functions. On the other hand, asynchronous operations allow a client to invoke a service and then execute other functions.
Answer: The web services protocol stack has four layers that help transport messages between applications. It includes:
- Service transport: It is the first layer of the web services protocol stack that transports XML files between several client applications. The following are the protocols used in this layer:
- HTTP or Hypertext transfer protocol
- SMTP or Simple Mail Transfer Protocol
- FTP or File Transfer Protocol
- BEEP or Block Extensible Exchange Protocol
- XML Messaging: This is the second layer based on the XML model, where messages get encoded into a common XML format that is easy to understand for other client applications. It includes the following protocols:
- XML– RPC
- SOAP or Simple Object Access Protocol
- Service Description: This layer offers the service description to the public interface, such as the web service’s location, data types, & available functions for the XML messaging. This layer only includes a language: WSDL or Web Service Description Language.
- Service Discovery: This layer is used for finding or publishing web services over the web. It has UDDI or Universal Description, Discovery, & Integration.
Answer: The Remote procedure call refers to a call made to the methods hosted by a related web service. It a robust technique for building distributed & client-server-based applications. RPC is based on extending the conventional notion or a local procedure calling, so the called procedure does not exist in the same address space similar to the calling procedure. By using RPC, programmers of distributed apps avoid the interface details with the network. The transport independence of RPC isolates an application from the logical & physical elements of the data communication mechanism & enables the application to use a variety of transports.
Answer: A SOAP message is an XML document containing a SOAP envelope, a SOAP body, & an optional SOAP header. The SOAP message header has the information that enables the message to be routed via multiple intermediate nodes before reaching its final destination.
Answer: The web service framework consists of three different layers:
- Service Provider: It is responsible for building the web service accessible to client applications over the web.
- Service Requestor: It refers to a consumer of a web service such as a client application. The client applications written in any language contact a web service for some functionality by sending an XML request over the network.
- Service Registry: Service Registry means a centralized directory system that helps locate web services for client applications. It is used to find an existing web service & developers can also create a new web service.
Answer: The main role of a Web Service Requestor / Consumer is to use the pre-existing web services provided by the Web Service Provider/ Publisher. It requests the Web Service provider for the needed information by sending a SOAP message & in turn, the Web Service Publisher sends back the requested information to the requestor in the form of a SOAP message.
Answer: RESTful web services use the HTTP protocol. It serves as the medium of data communication between the server & the client. HTTP standard methods are used to access resources in RESTful web service architecture.
Answer: Each RESTful web service has the following features as below:
- It is based on the client-server representation.
- RESTful web service uses an HTTP protocol for performing functions like retrieving resources, query execution, fetching data from the web service, etc.
- The communication between a client & server is performed through the medium called ‘messaging.’
- The RESTful web services address resources available on the server via URIs.
- It is based on the concept of statelessness wherein each client requests & the response is independent of each other with complete assurance of providing required information.
- It uses the concept of caching & works on the UI.
Answer: Statelessness means that each HTTP request occurs in complete isolation. When a client makes the HTTP request, it includes all the information required for the server to fulfill that request. The server never relies on the information from the previous requests.