Are you preparing for REST API interview? We’ve compiled a list of over 60+ essential REST API interview questions and answers for both freshers and experienced developers. This guide includes key concepts ranging from the basics of REST architecture to advanced topics like API security and performance optimization.
Rest API interview questions and answers for all levels
1. What is a REST API?
2. What are the key principles of REST architecture?
3. Explain the difference between PUT and POST methods?
4. What is the purpose of HTTP status codes in REST APIs?
5. List some common HTTP status codes and their meanings?
6. What is meant by ‘statelessness’ in REST?
7. What are the main HTTP methods used in REST APIs?
8. What is JSON, and why is it commonly used in REST APIs?
9. How is REST different from SOAP?
10. Explain the concept of a resource in REST?
11. What is URI and URL in REST?
12. How can you handle errors in RESTful APIs?
13. What is idempotency, and which methods are idempotent?
14. How would you secure a REST API?
15. What is CORS, and why is it important?
16. What is the difference between JSON and XML in REST?
17. Explain the concept of pagination in REST APIs.
18. What are query parameters in REST?
19. How would you design a RESTful API endpoint for a resource?
20. What is the use of HTTP headers in REST API?
21. What is HATEOAS in REST API?
22. What is API versioning, and why is it necessary?
23. What are some common security concerns with REST APIs?
24. What is JSON Web Token (JWT)?
25. Explain how API throttling works?
26. What is a RESTful API response format?
27. What is OAuth, and how does it work with REST APIs?
28. How would you log requests in a REST API?
29. What is the role of middleware in REST APIs?
30. How do you test REST APIs?
Advanced- Rest API interview questions and answers
1. What is RESTful API design, and why is it important?
2. What are the different types of API versioning, and when would you use each?
3. How would you approach API pagination and limit/offset in a REST API?
4. What are best practices for designing RESTful endpoints?
5. Explain the purpose and use of PATCH in REST APIs.
6. How would you handle long-running tasks in a REST API?
7. Describe how to implement caching in REST APIs and its advantages.
8. How does HATEOAS enhance REST API usability?
9. What are the main security mechanisms you would implement in a REST API?
10. Explain the use of OPTIONS method in REST APIs.
11. What is a rate limiter, and why is it essential for REST APIs?
12. How do you prevent over-fetching and under-fetching in REST APIs?
13. What is content negotiation, and how is it handled in REST APIs?
14. How do you implement idempotency in REST APIs?
15. What are the common REST API documentation tools?
16. How would you handle API versioning when deprecating old endpoints?
17. What are some best practices for error handling in REST APIs?
18. Explain the use of ETag headers in REST APIs.
19. How does OAuth 2.0 work in securing REST APIs?
20. What is a RESTful API gateway, and what are its benefits?
21. How do you scale a REST API?
22. What is a shadow API, and how can it impact security?
23. What is JSON Schema validation, and why is it used in REST APIs?
24. How does API gateway authentication work with REST APIs?
25. Explain the purpose of Accept and Content-Type headers.
26. What are JWT claims, and how are they used in REST APIs?
27. What is request throttling, and why is it necessary for API performance?
28. How would you structure a REST API for a microservices architecture?
29. Explain how OAuth 2.0 and OpenID Connect work together in REST APIs.
30. How do you manage API request timeouts and retries?
31. What is the HEAD method in REST APIs?
32. Explain the importance of consistent naming conventions in REST APIs.
1. What is a REST API?
Answer:
REST (Representational State Transfer) API is a web service architecture that uses HTTP methods to perform CRUD (Create, Read, Update, Delete) operations. RESTful services are stateless and provide a standard way for applications to communicate over HTTP.
2. What are the key principles of REST architecture?
Answer:
The key principles include stateless communication, client-server separation, cacheable data, uniform interface, layered system, and code on demand (optional).
3. Explain the difference between PUT and POST methods.
Answer:
POST creates a new resource and is often used for submission, while PUT updates an existing resource. POST requests usually don’t specify the URL for the created resource, while PUT requests usually include the resource identifier.
4. What is the purpose of HTTP status codes in REST APIs?
Answer:
HTTP status codes help clients understand the outcome of a request, whether it’s successful (200s), requires redirection (300s), resulted in a client error (400s), or encountered a server error (500s).
5. List some common HTTP status codes and their meanings.
Answer:
- 200 OK: The request was successful.
- 201 Created: A resource was successfully created.
- 400 Bad Request: The request was malformed.
- 401 Unauthorized: Authentication is required.
- 404 Not Found: The requested resource doesn’t exist.
- 500 Internal Server Error: The server encountered an error.
6. What is meant by ‘statelessness’ in REST?
Answer:
Statelessness means that each request from a client to the server must contain all necessary information for the server to fulfill the request. The server doesn’t store any session data between requests.
7. What are the main HTTP methods used in REST APIs?
Answer:
- GET: Retrieve data from the server.
- POST: Submit data to the server to create a resource.
- PUT: Update an existing resource.
- DELETE: Remove a resource from the server.
8. What is JSON, and why is it commonly used in REST APIs?
Answer:
JSON (JavaScript Object Notation) is a lightweight data format that’s easy for humans to read and for machines to parse. It’s commonly used in REST APIs due to its simplicity and interoperability.
9. How is REST different from SOAP?
Answer:
REST is a lightweight architecture based on HTTP, using JSON or XML formats, and is easier to implement. SOAP is a protocol with strict standards, uses XML exclusively, and often requires additional overhead, making it more suitable for enterprise-level applications.
10. Explain the concept of a resource in REST.
Answer:
In REST, a resource represents any information or object that can be accessed via a unique URL, such as a user profile, product details, or an article. Each resource is identified by a URI (Uniform Resource Identifier).
11. What is URI and URL in REST?
Answer:
URI (Uniform Resource Identifier) is a unique identifier for a resource, while a URL (Uniform Resource Locator) specifies the location of the resource on the server.
12. How can you handle errors in RESTful APIs?
Answer:
Error handling in REST APIs is done using HTTP status codes and JSON responses containing error messages and codes to inform the client about the issue.
13. What is idempotency, and which methods are idempotent?
Answer:
Idempotency means that multiple identical requests have the same effect as a single request. Methods like GET, PUT, and DELETE are idempotent, whereas POST is not.
14. How would you secure a REST API?
Answer:
REST APIs can be secured using authentication (such as OAuth, JWT), authorization (roles, permissions), HTTPS for secure communication, input validation, and rate limiting.
15. What is CORS, and why is it important?
Answer:
CORS (Cross-Origin Resource Sharing) is a security feature that allows or restricts resources on a web page to be requested from another domain. It’s important to control who can access the API from different origins.
16. What is the difference between JSON and XML in REST?
Answer:
JSON is a lightweight, easily readable format often preferred in REST APIs due to its simplicity and speed. XML is more verbose and supports additional features like namespaces and schemas, making it more complex.
17. Explain the concept of pagination in REST APIs.
Answer:
Pagination is a technique to divide large sets of data into smaller parts (pages) and send them incrementally. It reduces response time and server load and is typically implemented with query parameters like page and limit.
18. What are query parameters in REST?
Answer:
Query parameters are parts of the URL appended after a ? character, used to filter, sort, or specify additional options for the resource, such as /users?role=admin&page=2.
19. How would you design a RESTful API endpoint for a resource?
Answer:
RESTful API endpoints follow a standard pattern using nouns rather than verbs, e.g., /api/users for retrieving users and /api/users/{id} for specific user details. HTTP methods define actions like GET, POST, PUT, DELETE.
20. What is the use of HTTP headers in REST API?
Answer:
HTTP headers pass additional information with HTTP requests and responses, such as Content-Type, Authorization, and Accept, to define content type, authentication, and acceptable formats.
21. What is HATEOAS in REST API?
Answer:
HATEOAS (Hypermedia as the Engine of Application State) is a constraint of REST where responses contain links to related resources, allowing clients to navigate the API dynamically without hardcoding URLs.
22. What is API versioning, and why is it necessary?
Answer:
API versioning allows developers to make backward-incompatible changes to an API without breaking existing client implementations. It’s achieved by including versions in the URL (e.g., /api/v1/users).
23. What are some common security concerns with REST APIs?
Answer:
Common concerns include data breaches, exposure of sensitive data, improper authentication and authorization, lack of encryption (HTTPS), SQL/NoSQL injection, and cross-site scripting (XSS).
24. What is JSON Web Token (JWT)?
Answer:
JWT is a compact, URL-safe token used for securely transmitting information between parties, often for authentication in REST APIs. It consists of three parts: header, payload, and signature.
25. Explain how API throttling works.
Answer:
API throttling limits the number of requests a client can make to a server within a time period. This prevents abuse and overuse of resources, enhancing the API’s stability.
26. What is a RESTful API response format?
Answer:
RESTful responses are typically in JSON format, with key-value pairs for resource data. The response should also include HTTP status codes, metadata, and sometimes hypermedia links.
27. What is OAuth, and how does it work with REST APIs?
Answer:
OAuth is an open-standard authorization protocol that allows third-party applications to access user data without exposing passwords. It generates access tokens for secure access to protected resources.
28. How would you log requests in a REST API?
Answer:
Logging requests involves recording details such as request method, URI, status codes, timestamps, IP addresses, and payloads for monitoring and debugging. Logging frameworks can automate this.
29. What is the role of middleware in REST APIs?
Answer:
Middleware in REST APIs intercepts requests and responses, performing tasks like logging, authentication, validation, and error handling before passing control to the next function or returning a response.
30. How do you test REST APIs?
Answer:
REST APIs can be tested using tools like Postman or automated frameworks like REST Assured for verifying endpoints, response status, payload structure, headers, and performance under various conditions.
Advanced- Rest API interview questions and answers
1. What is RESTful API design, and why is it important?
Answer:
RESTful API design involves creating APIs that adhere to REST principles for easy use, scalability, and maintenance. Good design minimizes coupling, enhances API readability, supports caching, and ensures stateless interactions, resulting in robust and intuitive APIs.
2. What are the different types of API versioning, and when would you use each?
Answer:
- URI versioning: Adding the version in the URL (e.g.,
/v1/resource). Used when major changes occur. - Header versioning: Specifying the version in the header. Useful for more complex versioning.
- Query parameter versioning: Versioning through query parameters (e.g.,
/resource?version=1). Useful for minor changes. - Media type versioning: Defining the version in the
Acceptheader with media types (e.g.,application/vnd.api.v1+json).
3. How would you approach API pagination and limit/offset in a REST API?
Answer:
Pagination can be handled with query parameters such as limit (items per page) and offset (items to skip), or by using page and perPage. For large data sets, cursor-based pagination is efficient, as it references specific data points rather than offsets, making it performant on large datasets.
4. What are best practices for designing RESTful endpoints?
Answer:
Use nouns for resource names, maintain consistent naming conventions, avoid verbs, use hierarchical structure, ensure endpoints are versioned, use query parameters for filtering/sorting, and leverage proper HTTP methods for clarity.
5. Explain the purpose and use of PATCH in REST APIs.
Answer:
The PATCH method performs partial updates on a resource, modifying only the specified fields rather than replacing the whole resource, as with PUT. This reduces data transfer and is useful for minor updates.
6. How would you handle long-running tasks in a REST API?
Answer:
For long-running tasks, initiate the task asynchronously and return a 202 Accepted status with a URL to poll the task status. Once complete, clients can retrieve the final results.
7. Describe how to implement caching in REST APIs and its advantages.
Answer:
Caching can be implemented by setting appropriate HTTP headers like Cache-Control, ETag, Last-Modified, and Expires. It improves performance, reduces latency, and lowers server load by reusing previous responses.
8. How does HATEOAS enhance REST API usability?
Answer:
HATEOAS (Hypermedia as the Engine of Application State) provides discoverability by including links to related resources in responses, allowing clients to navigate APIs dynamically without hardcoding URLs.
9. What are the main security mechanisms you would implement in a REST API?
Answer: Security mechanisms include:
- Authentication: OAuth 2.0, JWTs, API keys.
- Authorization: Role-based access control.
- HTTPS: To secure data in transit.
- Rate limiting: To prevent abuse.
- Input validation: To prevent injection attacks.
- CORS: For cross-origin security.
10. Explain the use of OPTIONS method in REST APIs.
Answer:
OPTIONS is used to describe the communication options for a resource. It often returns the allowed HTTP methods, and in CORS, it’s used for preflight requests to check server permissions for cross-origin requests.
11. What is a rate limiter, and why is it essential for REST APIs?
Answer:
A rate limiter restricts the number of requests a client can make in a given timeframe to prevent abuse and ensure fair usage across clients. Rate limits protect resources from being overwhelmed and ensure service stability.
12. How do you prevent over-fetching and under-fetching in REST APIs?
Answer: Over-fetching (retrieving more data than needed) and under-fetching (retrieving less data) can be mitigated with:
- Sparse fieldsets: Allow clients to request specific fields.
- Filtering: Use query parameters to retrieve only relevant data.
- GraphQL or similar technologies: When precise data requirements are frequent and complex.
13. What is content negotiation, and how is it handled in REST APIs?
Answer:
Content negotiation allows clients to specify response format preferences using Accept headers (e.g., JSON or XML). The server responds based on the client’s specified Accept header or defaults if not provided.
14. How do you implement idempotency in REST APIs?
Answer:
Idempotent operations (e.g., GET, PUT, DELETE) can be retried without changing the result. For non-idempotent methods like POST, idempotency can be implemented using unique request IDs or idempotency keys to avoid duplicate processing.
15. What are the common REST API documentation tools?
Answer: Tools include:
- Swagger/OpenAPI: Provides interactive documentation and endpoint details.
- Postman: Allows for creating and sharing API documentation.
- API Blueprint and RAML: Text-based documentation formats.
16. How would you handle API versioning when deprecating old endpoints?
Answer:
Inform clients with deprecation notices and provide clear upgrade paths. Implement versioning strategies, and phase out deprecated versions after a grace period with notifications or sunset headers.
17. What are some best practices for error handling in REST APIs?
Answer:
Error responses should use standard HTTP status codes, meaningful error messages, and consistent error format (e.g., with fields like error, message, status). Include trace identifiers for debugging.
18. Explain the use of ETag headers in REST APIs.
Answer:
ETag (Entity Tag) headers serve as a unique identifier for a specific resource version. When combined with conditional requests (using If-None-Match), they optimize performance by only sending the resource if it has changed.
19. How does OAuth 2.0 work in securing REST APIs?
Answer:
OAuth 2.0 is an authorization protocol that provides limited access tokens, allowing third-party applications access to resources without exposing user credentials. Access tokens are issued and can expire or be refreshed for security.
20. What is a RESTful API gateway, and what are its benefits?
Answer:
An API gateway is a layer that sits between clients and microservices, managing request routing, security, rate limiting, and analytics. It simplifies service discovery and enhances security and scalability.
21. How do you scale a REST API?
Answer: Scaling can involve:
- Horizontal scaling: Adding more instances of the API server.
- Caching: Reducing database load.
- Load balancing: Distributing requests.
- Database optimization: Using replicas and indexing.
- Async processing: Offloading heavy tasks.
22. What is a shadow API, and how can it impact security?
Answer:
A shadow API is an undocumented or unknown API endpoint that can expose vulnerabilities if not secured. Regular auditing and documentation practices help identify and protect shadow APIs.
23. What is JSON Schema validation, and why is it used in REST APIs?
Answer:
JSON Schema defines the expected structure of JSON data, enabling input validation and error prevention. It ensures client requests are correctly structured and APIs respond with predictable outputs.
24. How does API gateway authentication work with REST APIs?
Answer:
An API gateway authenticates clients by handling security tokens (like JWTs), API keys, or OAuth access tokens. It routes only authenticated requests, centralizing security management.
25. Explain the purpose of Accept and Content-Type headers.
Answer:
- Accept: Specifies the media types that the client can process (e.g., JSON).
- Content-Type: Indicates the media type of the request body for the server to parse.
26. What are JWT claims, and how are they used in REST APIs?
Answer:
JWT claims are key-value pairs in JWTs. They contain information about the user (subject, expiration, permissions). REST APIs use claims to verify user identity, permissions, and session validity.
27. What is request throttling, and why is it necessary for API performance?
Answer:
Request throttling limits request rates to control resource use, maintain stability, and prevent DDoS attacks. Limits are usually set based on client IP, user, or application.
28. How would you structure a REST API for a microservices architecture?
Answer:
APIs should follow a domain-driven design, with each service owning specific data and endpoints. An API gateway can manage routing, security, and orchestration between microservices.
29. Explain how OAuth 2.0 and OpenID Connect work together in REST APIs.
Answer:
OAuth 2.0 handles authorization, while OpenID Connect adds an authentication layer. Combined, they allow users to securely log in, provide identity data, and authorize resource access.
30. How do you manage API request timeouts and retries?
Answer:
Request timeouts ensure that clients don’t wait indefinitely, and retries handle transient failures. Use exponential backoff or circuit breakers to manage retries without overloading the server.
31. What is the HEAD method in REST APIs?
Answer:
HEAD requests retrieve headers for a resource without the body. It’s useful for checking metadata or availability without transferring full data.
32. Explain the importance of consistent naming conventions in REST APIs.
Answer:
Consistent naming conventions improve API readability and maintainability. Using meaningful, consistent names (like plural nouns for resources) avoids ambiguity and ensures intuitive endpoints.
These advanced questions aim to test in-depth understanding, best practices, and real-world application of RESTful API principles and methods. They are valuable for identifying experienced candidates with expertise in API design, security, and optimization.
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