Top 25 REST API Interview Questions and Answers in 2024

Editorial Team

REST API Interview Questions and Answers

REST, fully known as Representational State Transfer, revolutionized the APIs world. Thanks to it, we have trends like microservices-based architecture and cloud computing which were foreign two decades ago. These APIs have made it easy to communicate and computer over the web, explaining their importance.

Most software development firms or related jobs need people with REST knowledge given the role this API plays in developing scalable and easy-to-maintain products. We will make your work easier and help you prepare by looking at some of the questions you should expect in your upcoming interview. Brainstorm on the following:

1. Define Restful Web Services

REST offers an architecture used to build services known as RESTful web services. They use HTTP or the web protocol for implementation purposes. These services are easy to maintain, scalable, lightweight, and offer communication support among several applications. You will easily access resources from the web browser, thanks to them.

2. Define URI

URI fully stands for uniform resource identifier. As the name suggests, it is used to identify all the resources in the REST architecture. URIs are normally grouped into two, URL and URN. URN, the uniform resource name, is used to identify a resource based on its unique and persistent name. However, they do not specify the location of a given resource but act as templates that aid in identifying the resource. After document identification, the URL translates it for download through its resolver function.

On the other hand, URL stands for uniform resource locators, which store information required to fetch a resource from a given location.

3. You Have Mentioned Resources Severally In Your Answers. Can You Define What They Are?

In the REST API, any existing content is known as a resource, which is analogous to an object where object-oriented programming is used. These resources are commonly represented as HTML pages, text files, and images, among many other dynamic data types.   The API has a server permitting access to these resources, which are then relayed to a client. It is worth mentioning that these resources can be globally identified using a URI.

4. Can You Mention The Features Of Restful Web Services?

All the RESTful web services have similar features. They are based on the cloud-server model, use HTTP to find data resources and query execution, and use a similar communication medium between clients and servers, popularly known as messaging. These services also access resources via URI, rely on the caching concept, which minimizes server calls depending on the situation, and uses SOAP services as implementation protocol.

5. Can You Mention The Different HTTP Status Codes?

Status Codes are found at the server, referring to different tasks’ predefined statuses. They come in five formats, i.e., 1xx, 2xx, 3xx, 4xx, and 5xx. The first represents informational responses, the second successful responses, the third redirects, the fourth client errors, and finally, 5xx represents errors with the server. Some common status Codes in this protocol are 200 for success, 201- CREATED uses in PUT and POST methods, 400-BAD REQUEST, which shows validation error or missing data, and 404- NOT FOUND, which shows that a given resource is unavailable. Other status codes are 502- BAD GATEWAY, 401- UNAUTHORIZED, and 403-FORBIDDEN.

6. Mention The Different HTTP Methods

Also known as HTTP verbs, HTTP Methods dictate the action that should be followed depending on the requested resource, contributing to a uniform interface. Some of the common HTTP methods are GET, a read-only operation that retrieves details from a given server; DELETE, which deletes resources on a server, OPTIONS which retrieves all the supported resource options found on the server, PATCH, which modifies server resources, PUT that updates an existing resource on the server and POST that creates new server resources.

7. Even Though Restful Services Have Several Advantages; They Also Come With Limitations. Can You Please Mention The Disadvantages Of These Services?

There are two main advantages of RESTful services. This API cannot inherently impose security restrictions, which is quite disadvantageous. Instead, the security measures are inherited from the implementing protocols, which means that a developer must be extra careful. The services also work on the idea of statelessness, which makes it impossible to maintain sessions. The client must pass the session ID for session simulations.

8. Mention The Differences Between SOAP And REST

There are several differences between SOAP, fully known as Simple Object Access Protocol, and REST, which is representational stay transfer. As the names imply, SOAP is a protocol for web services implementation, while REST is an architectural design pattern that empowers the building of web services. It is impossible for SOAP to rely on REST as its protocol, while REST can use SOAP as one of its protocols. SOAP is also quite strict in the standards to be followed, while the standards defined by REST don’t have to be strictly followed. Lastly, SOAP has tight client-server coupling, whereas REST offers flexibility to the client.

9. What Makes An HTTP Request?

An HTTP Request has several components. It is made up of the method/verb like GET, PUT, and POST, which are the methods represented by the request operation; the HTTP version, which shows the HTTP protocol version in use; the request body that captures the actual message relayed to the server, request header which holds the request metadata details such as the supported format and client type and lastly, the URI which uniquely identifies server resources.

10. Now That You Have Mentioned The Components Of An HTTP Request, What Makes UP An HTTP Response?

HTTP responses have four main components: the response status code, the response body, the HTTP version, and the response header. The actual body is the message retrieved from the server to be relayed to the client, while the response header contains the metadata of a given response message. It covers the content length, type, server type, and server data. The HTTP version is the protocol’s version, while the Response status code shows the server status code for a given requested resource.

11. What Best Practices Do You Follow When Creating URI For Web Services?

I normally have a set of best practices that I adhere to when creating web services’ URIs. First, I normally ensure that a plural noun is used when defining resources. I also use lower case since the URI is generally case-sensitive. Other best practices that have helped me in creating web services’ URI are using a hyphen or underscore when giving the resources long names, maintaining backward compatibility when developing URI given that an older URI must be redirected through the status code 300 when a URI is updated or a new one created, forward slashing that shows hierarchy between resources and collections and lastly, using the right HTTP Methods.

12. Differentiate Between REST And AJAX

There are three main differences between REST, Representational State Transfer and AJAX, Asynchronous JavaScript, and XML. The former has a URI that lets it access resources, while AJAX relies on an HTMLHttpRequest to communicate with the server, after which requests are dynamically interpreted by the JavaScript code. REST’s operating mechanism further demands constant interaction between clients and servers, which doesn’t apply in AJAX since all the asynchronous requests have been replaced. Lastly, AJAX dynamically updates user interfaces, saving them from reloading the page, while the former is an architectural pattern that develops client-server communication systems.

13. Differentiate Between PUT And POST

PUT and POST are common HTTP Methods that serve different functions. Whereas PUT methods request servers to store enclosed entities in a request, POST requests a server to store the enclosed entity as a new resource. PUT, therefore, has a resource identifier, while the POT URI is required to indicate the resource collection. PUT methods are also idempotent even though they don’t cache responses, while POST is not idempotent and can cache responses under given conditions. Lastly, PUT performs UPDATE operations while POST handles CREATE operations.

14. What Should One Consider When Choosing Between REST And SOAP?

Both REST and SOAP have their preferred use cases, meaning one shouldn’t pick either blindly. REST services are generally simple, scalable, faster, better performing, and offer several data format support, while SOAP offers advanced security and is more reliable than its counterpart.

When choosing between the two, one should consider if there is a need to expose resource data or business logic where SOAP will come in handy for the latter and REST for the former; strict formal contact requirements by the client where SOAP wins as it uses WSDL; support for several data formats which TEST perfectly does; stateless requirement where REST is suitable and high-level security requirement where SOAP is advisable. Other factors to consider are support for transactions, the bandwidth required, types of services needed, synchronous and asynchronous services requirement, and the need for AJAX support.

15. Is It Possible To Implement Transport Layer Security, Popularly Known As TLS In REST?

Yes. The transport security layer encrypts communication between the client and server, thus allowing server authentication. It offers secure communication as it succeeds the Secure Socket Layer, popularly known as the SSL. Such security measures depend on the implemented protocols, given that REST inherits all the properties of the implemented protocol.

16. In Your Opinion, What Is The Best Way Of Testing Restful Web Services?

RESTful web services can be tested using various tools such as Swagger and Postman. Swagger allows the sending of a request to the endpoints and, finally, the response to be converted to XML or JSON. It also has features that inspect different parameters, such as headers and queries. Postman also has similar features to Postman. Another important tool is JMeter, which comes in handy in performance and load testing.

17. Describe How HTTP Basic Authentication Works

Basic Authentication is implemented as part of an API when a user keys in their username and password concatenated as “username: password” by the browser before base64 encoding is done. After encoding, the value is relayed as the authorization header value to every HTTP Request emanating from the browser. Basic Authentication is highly advised since requests sent over the HTTP are generally insecure and are therefore vulnerable to interception.

18. It Is Possible To Develop Webservices With Web Sockets Too. Can You Mention The Differences Between Web Sockets And REST?

REST has a stateless architecture and can’t store session-based data, while WebSockets APIs have a stateful protocol since session-based data must be stored. REST generally relies on the request-response mechanism, while Web Sockets rely on the full-duplex method. Also, REST has a uni-directional mode of communication, meaning that the server and client can’t communicate simultaneously, while Web Socket supports bidirectional communication where the server and client can communicate at a particular time. Other differences include: REST has slower communication, does not need memory or buffers to store data, and depends on HTTP Methods for responses, while Web Socket has faster message transmission, requires memory to store data, and depends on an IP address and port number for response generation.

19. What Are Some Of The Best Practices That Should Be Observed When Creating Restful Web Services?

Good practices should be followed when building RESTful web services to ensure the creation of safe and secure REST application program interfaces. The final REST API should be able to work with the JSON data format where needed, given that JSON is nowadays more of a standard object notation. Also, plural nouns should be used when naming resource endpoints instead of verbs to ensure that the API endpoint is informative, brief, easy to understand, and clear. Where there is a need to represent the hierarchy of resources, the nesting found in the endpoints’ conventions should be used.

20. Why Is The Caching Feature And Good Security Practices Important When Creating REST APIs?

A developer must adhere to good security practices when creating REST APIs by incorporating TLS/SSS during the development, thus establishing secure communications. The resources should not also be accessible to everyone with an internet connection; therefore, role-based access controls should be used.

Caching, supported by REST, ensures improved application performance and promotes faster data retrieval. The cache should have updated data at all times.

21. What Makes It Necessary To Filter And Paginate Resources?

It is important to filter and paginate resources when retrieving relatively larger data resources to prevent slowing down the system. A system generally slows down and witnesses reduced performance when huge data amounts of data are returned simultaneously. Filtration reduces data to a given percentage, while pagination prevents the sending or return of all results. These two practices reduce the burden placed on the resources and, in return, increase server performance.

22. Define Idempotent Methods

Idempotence ensures the return of a similar result even after calling a single request several times, making it an important consideration when creating APIs. Idempotent APIs prevent incorrect responses since clients can create duplicate requests from the codes they write. Idempotent methods ensure that request responses are similar regardless of the times they are called. These REST methods are HEAD, OPTIONS, DELETE, PUT and TRACE. POST does not, however, fall in this category given that their APIs create new resources on a server, meaning that there will be new resources reflecting the number of times POST methods have been called.

23. How Should One Handle Error Handling When Creating Restful Web Services?

As a best practice, one must gracefully perform error handling during web service creation. REST normally comes with defined HTTP Status Codes that are returned with the responses depending on the scenario. The REST error codes should come with the right error message for proper corrective actions when handling errors. The message doesn’t have to be too detailed or simple, as it can empower hackers.

24. Is There A Difference Between Normal APIs And The REST API?

Yes. There are several differences between regular APIs and the REST API. Whereas APIs are normally meant to standardize the exchange of data between different web services, REST API takes it a notch further by offering an architectural style to be used in building web services whose interaction is based on an HTTP protocol. REST also differs from other APIs in its design, given that it is more complex, beating other APIs with lightweight designs. Furthermore, you don’t need to know the function names and order of parameters to execute REST API as opposed to other existing APIs. Lastly, REST API is more flexible and scalable than its counterparts, thanks to its layered structure.

25. Why Do We Need APIs?

There are many reasons for the existence of APIs. They are not only dynamic but can also automate workflows, thus allowing companies to achieve increased agility. Also, APIs play an important role in boosting data and server security as they act as extra security layers. Other benefits are improved efficiency and integration, explaining their popularity.


Remember to go through the questions we have covered even as you go through your REST API interview. Organizations need the most skilled, which is generally proven by how you answer interview questions. Therefore, put extra effort into your preparation and work on your confidence.