Introduction
If you’re preparing for software engineering or QA interviews in 2025, REST API questions will almost certainly be part of the discussion. REST remains the foundation of modern RESTful web services, powering everything from backend communication in microservices to integrations with third-party platforms. Interviewers want to see not only that you understand the core principles like statelessness, HTTP methods, and status codes, but also that you can apply them in practical scenarios. In this article, we’ll walk through the most common REST API interview questions and answers, giving you clear explanations, examples, and insights to help you stand out in your next interview.
REST API Fundamentals
If you’re walking into an API interview in 2025, expect a handful of REST API interview questions right at the start. Why? Because REST APIs are still the most common way developers build and consume web services. They’re simple, stateless, and designed for predictable communication between clients and servers. Whether you’re working on microservices, mobile apps, or internal dashboards, understanding how REST works and how to explain it clearly is going to help you stand out.
Most interview questions and answers around RESTful web services focus on the basics: HTTP methods, URIs, resources, and standard HTTP status codes. You should also be prepared to discuss error handling, API endpoints, and how concepts such as API versioning, authentication and authorization mechanisms, and cross-origin resource sharing (CORS) are applied. Let’s go through the fundamentals you’ll need to answer confidently.
What is a REST API and how does it work?
A REST API (short for Representational State Transfer) is an application programming interface that adheres to a set of principles governing how clients and servers communicate with each other. The key idea is statelessness: each HTTP request contains everything the server needs to process it, with no reliance on subsequent requests or session memory.
You hit an api endpoint (like /users/123) with a request, and the api server responds with a structured payload, usually in JavaScript Object Notation (JSON). This design makes restful APIs scalable and predictable, especially when managing web resources, which is exactly why you’ll see them powering everything from microservices to public APIs.
What are HTTP methods in REST APIs?
Every REST API interaction begins with an HTTP method (sometimes referred to as an HTTP verb) that specifies the expected HTTP response. These define what action you’re taking against a resource:
- GET → retrieve data without changing it
- POST → create something new
- PUT → fully update an existing resource
- PATCH → apply a partial update
- DELETE → remove a resource
Interviewers often ask about idempotency, which means that multiple identical requests should have the same outcome (e.g., PUT and DELETE are idempotent, whereas POST is not). Be ready to explain how these HTTP request methods tie directly to REST architecture and why using the right one keeps your api documentation and testing process clear.
What is a REST resource?
In RESTful APIs, a resource is just the thing you’re working with. It could be a user, a product, or even a webpage. Each one is identified by a Uniform Resource Identifier (URI). For example, /users/123 is a resource that represents a single user.
You interact with resources through HTTP requests, often passing query parameters or a request body to filter or change what you’re retrieving. Since responses are typically structured as key-value pairs in JSON, they’re easy to parse and reuse across web applications or server processes.
What are URI and URL in REST context?
This one frequently appears in REST API interview questions. A Uniform Resource Identifier (URI) is a string that uniquely identifies a resource. A URL (Uniform Resource Locator) is a specific type of URI that not only identifies the resource but also tells you how to reach it.
- URI: /users/123 → uniquely identifies a resource
- URL: https://api.example.com/users/123 → specifies the protocol, domain, and path to get the same resource
When discussing API endpoints, you’ll often see both terms, but in interviews, it’s useful to explain that all URLs are URIs, but not all URIs are URLs.
What are HTTP status codes and why are they important?
HTTP status codes tell the client how an http request turned out. They’re essential for error handling and for providing meaningful error messages in RESTful APIs. Some of the common status codes to know for interviews are:
- 200 OK → request was successful
- 201 Created → a new resource was created
- 400 Bad Request → client sent an invalid request
- 401 Unauthorized → missing or invalid credentials
- 404 Not Found → the requested resource doesn’t exist
- 500 Internal Server Error → something went wrong on the api server
Expect to receive follow-ups on distinguishing between client errors and server errors, when to use appropriate HTTP status codes, and how to enhance backward compatibility by returning error responses with detailed error messages in the response body. A good answer goes beyond listing codes, explaining why they matter for debugging, monitoring, and making your api requests reliable for authorized users and existing clients.
Design & Best Practices
When preparing for REST API interview questions, it’s not enough to know the fundamentals of REST APIs; interviewers will also want to see if you understand how to design resource-oriented architecture for RESTful web services that scale, follow best practices, and make life easier for developers and existing clients. Expect API interview questions about HTTP methods, status codes, api versioning, and how you’d handle error handling in production. This section covers the design concepts you should know to answer those interview questions and answers with confidence.
What are the best practices for designing RESTful APIs?
When designing RESTful APIs, keep your REST architecture predictable and easy to use. Some best practices to highlight in an API interview:
- Use nouns (not verbs) in your api endpoints: /users/123 instead of /getUser.
- Stick to standard HTTP methods like GET, POST, PUT, PATCH, and DELETE for actions.
- Always return appropriate HTTP status codes with clear response bodies and meaningful error messages.
- Support API versioning (e.g., /v1/users) to prevent changes from breaking existing clients and maintain backward compatibility.
- Document your API with clear examples of api requests, query parameters, and http request methods.
A clean design helps developers retrieve data, send payloads in a request body, and interpret HTTP responses without confusion, which is exactly what good RESTful APIs should do.
How do you handle versioning in REST APIs?
API versioning is a common rest api interview question because it’s critical for long-term maintainability. There are a few ways to version APIs:
- URI versioning: Include the version in the path → /v1/users.
- Query parameter versioning: Add a version parameter → /users?version=2.
- Header-based versioning: Use a custom request header like API-Version: 2.
Most developers prefer URI or header-based versioning since they’re explicit and easy to maintain. This ensures backward compatibility, allowing existing clients to continue using older versions while new features are shipped on a separate track. In interviews, be prepared to explain which approach you’d recommend and why.
What does idempotency mean in REST APIs?
Idempotency means that making multiple identical requests will always result in the same outcome. In RESTful APIs, this concept ensures reliability and predictability in automation and retry logic.
For example:
- Sending the same request body multiple times to PUT/users/123 will not change the result after the first update.
- DELETE /users/123 will always remove the resource, no matter how many times it’s called.
In contrast, POST is not idempotent because every call typically creates a new resource. Interviewers may connect this to error handling e.g., if a network issue forces a retry, idempotency prevents duplicate records or inconsistent server processes.
What’s the difference between PUT and POST?
This comes up in almost every rest api interview. Both HTTP methods update the server, but they serve different purposes:
- POST → Create a new resource. Example: POST /users with a request body adds a new user.
- PUT → Update or replace an existing resource. Example: PUT /users/123 replaces the user data with new values.
Some API interview questions will push further: PATCH methods allow partial updates, whereas PUT replaces the entire requested resource. Always be ready to explain why using the correct HTTP verbs improves clarity and prevents confusion for other developers consuming your API.
What are REST API rate limits?
Rate limits are a way to enforce fair usage of an API server by controlling how many API requests a client can make within a given timeframe. This prevents abuse, protects against denial-of-service attacks, and ensures server processes can handle load fairly across all authorized users.
For example, a service might limit api endpoints to 1000 HTTP requests per hour per client. If that limit is exceeded, the server may return a 429 Too Many Requests response, or even an internal server error if requests continue.
In interviews, expect follow-ups on how rate limits relate to error codes, providing meaningful error messages, and designing RESTful APIs that strike a balance between scalability, data protection, and developer experience.
Focused on API architecture, scalability, and clean design.
Security & Testing
No set of REST API interview questions would be complete without a focus on security and testing, including topics like basic authentication . Companies want to know you understand not just how REST APIs work, but also how to protect them from abuse, handle client errors and server errors, and validate responses. Expect API interview questions related to authentication and authorization mechanisms, CORS, and common testing tools such as Postman or cURL. Let’s break it down into the core areas interviewers care about.
How do you secure a REST API?
Securing RESTful APIs comes down to protecting data in transit and controlling who can access api endpoints. A good answer in an api interview includes:
- HTTPS → Encrypts all HTTP requests and HTTP responses so that sensitive data isn’t leaked.
- API keys or tokens → Used to authenticate authorized users making api requests.
- Input validation → Prevents injection attacks by sanitizing query parameters and request bodies.
- Rate limits → Helps enforce fair usage and prevents abuse.
You may also mention modern approaches, such as JSON Web Tokens (JWTs), or implementing token-based authentication with an authorization server and a resource server. If you can tie this back to providing meaningful error messages when credentials are missing or invalid, you’ll show a strong grasp of error handling in secure APIs.
What is the difference between authentication vs authorization in REST?
This is one of the most common rest api interview questions. Authentication answers who you are, while authorization answers what you can do.
For example:
- Authentication: You send an API token in the request header → the api server verifies it.
- Authorization: Based on that token, the server decides whether you can retrieve data, create, or delete a requested resource.
In a RESTful API, you typically authenticate once per request (since REST is stateless). Then the server applies authorization rules before executing the HTTP methods. Be ready to explain how these mechanisms protect web services and maintain secure data transmission.
How do you test a REST API?
For testing, you want to demonstrate familiarity with real developer tools. The most common ones to mention in an api interview are:
- Postman → Easy GUI for sending HTTP requests, testing status codes, and checking the response body.
- curl → Command-line tool to hit api endpoints directly (great for debugging).
- Automated test frameworks → Using Java, Python, or JavaScript libraries to script api requests and validate responses.
Testing should cover error handling (checking for appropriate HTTP status codes like 400, 401, 404, 500), response headers, and detailed error messages in the response body. Strong candidates also mention how automated tests can simulate subsequent requests, measure test execution speed, and validate backward compatibility for existing clients.
What is CORS, and how does it affect REST APIs?
Cross-Origin Resource Sharing (CORS) is a browser security feature that restricts how web applications running in one domain can make HTTP requests to an api endpoint hosted on another domain.
Without proper CORS headers (Access-Control-Allow-Origin), browsers will block requests for security reasons, which relates to the fair usage policy. This comes up frequently in API interview questions because, if you’re exposing a web service API that frontend apps consume, you need to configure CORS policies correctly.
For example, allowing requests only from authorized users on trusted domains prevents abuse while still letting legitimate apps exchange data with your RESTful APIs.
Real-World Scenarios & Advanced Concepts
Once you’ve mastered the fundamentals, many REST API interview questions dive into applied use cases and advanced concepts. Employers want to see that you not only understand how RESTful APIs are designed, but also how they behave in production environments with real-world web services. Expect api interview questions about payloads, HTTP request methods, distributed server processes, and best practices for error handling. Let’s go through the key areas that often come up in advanced rest api interview discussions.
What is a REST API payload?
A REST API payload is the data sent by the client to the api server in a request body. Most often, the payload is structured as JavaScript Object Notation (JSON), a lightweight data interchange format made up of key-value pairs.
For example, if you’re creating a user, you might send:
In interviews, emphasize that payloads are not just about data transmission, they allow clients to send configurations, filters, or state changes to an api endpoint, making them central to how RESTful web services exchange data.
Can you send a payload with GET or DELETE?
This is a common api interview trick question. By design, standard HTTP methods like GET and DELETE should not include a request body. GET is meant to retrieve data, and DELETE is meant to remove a requested resource. Payloads in these methods are technically possible on some servers, but they’re not standard and are often overlooked.
The correct approach is to stick to POST (for creation) or PUT/PATCH methods (for updates) when sending payloads. This aligns with the rest of the architecture and avoids compatibility issues across different api servers and web service APIs. You can also mention using query parameters in GET requests for filtering instead of payloads.
How does Browserless use REST APIs to scale headless browser tasks?
This is where real-world application shines. Browserless, a platform for headless Chrome and Playwright/Selenium automation, relies on REST APIs to distribute browser automation workloads. Because REST APIs are stateless and built on a solid REST architecture, each HTTP request to an API endpoint, such as/screenshot or /scrape, contains all the necessary configuration in the request body.
That means tasks like rendering a webpage, generating PDFs, or scraping structured content can be distributed across multiple machines in the cloud without depending on subsequent requests or shared session state. This architecture allows Browserless to handle parallel test execution, scalable test automation, and high-throughput web scraping workloads reliably. For interviews, mentioning this type of distributed RESTful API design demonstrates your understanding of how APIs support real-world scaling.
How do you handle errors in REST APIs?
Good error handling is a sign of a well-designed REST API. Instead of returning generic failures, APIs should return appropriate HTTP status codes with clear response bodies that contain error codes and meaningful error messages.
For example:
Here’s what to highlight in an api interview:
- Use client errors (4xx) when the issue is with the request.
- Use server errors (5xx) when something fails inside the server processes.
- Always return structured JSON so clients can parse and act on errors programmatically.
- Document common status codes and error patterns in your api documentation.
Browserless, for example, returns JSON with structured error details, making debugging and retries straightforward. This is exactly the type of real-world REST API design interviewers want to hear about.
Conclusion
Mastering REST APIs is a must-have skill for modern developers, whether you’re preparing for interviews or building production-ready systems. From HTTP methods and status codes to error handling and API versioning, these fundamentals demonstrate how to design and work with scalable RESTful web services. And it’s not just theory. Platforms like Browserless demonstrate how REST APIs drive real-world automation, enabling you to run scraping jobs, generate PDFs, and scale headless browser sessions with simple, stateless calls. Ready to put your knowledge into practice? Sign up for a free Browserless trial and see how REST powers production-grade automation at scale.
FAQs
How should I prepare for REST API interview questions in 2025?
When preparing for REST API interview questions, start with the fundamentals of RESTful web services and understand how HTTP requests, HTTP responses, and HTTP methods (GET, POST, PUT, DELETE) work with an api endpoint. Review status codes, especially client errors (4xx) and server errors (5xx) like 500 Internal Server Error, and practice explaining them with real-world examples. Employers often ask API interview questions around error handling, api versioning, and backward compatibility, so make sure you can confidently explain these concepts with examples.
What are the most common API interview questions I should expect?
In a REST API interview, expect questions around:
- Explaining REST architecture and Representational State Transfer principles
- How Uniform Resource Identifiers (URIs) define a requested resource
- The difference between standard HTTP methods like PUT and PATCH methods
- Returning appropriate HTTP status codes with clear response bodies
- Implementing authentication and authorization mechanisms (e.g., API keys, tokens, or JSON Web Tokens)
Some interviews also ask you to compare REST with Simple Object Access Protocol (SOAP) to test your knowledge of legacy web service APIs.
How important is it to know HTTP status codes for an API interview?
Understanding HTTP status codes is critical for success in an API interview. You should be able to map HTTP request methods to the right status codes: 200 OK for successful data retrieval, 201 Created for resource creation, 400 Bad Request for malformed input, and 500 Internal Server Error for unexpected failures in server processes. Being able to explain why using appropriate HTTP status codes improves api documentation, debugging, and reliability will set you apart.
Do I need to study advanced topics like API versioning and CORS for API interviews?
Yes. Many api interview questions go beyond basics. Be prepared to explain api versioning (e.g., URI versioning like /v1/users or query parameter versioning like /users?version=2) and why it matters for backward compatibility with existing clients. You should also understand Cross-Origin Resource Sharing (CORS) since it affects how browsers consume web services. Being able to connect these concepts to real-world RESTful APIs shows you’re interview-ready.
How can I effectively practice answering REST API interview questions?
The best way to prepare is to practice answering interview questions out loud. Use tools like Postman or curl to send api requests with different request bodies, query parameters, and request headers, then analyze the HTTP responses and response headers. Document what happens when you send multiple identical requests (e.g., idempotency with PUT), or when you hit api endpoints that return error codes. Reviewing api documentation for real-world RESTful APIs will also help you understand how developers communicate data formats, key-value pairs, and meaningful error messages.