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REST API Interview Questions and Answers 2026 - Top 10 Web Services Questions - Admin - 03-21-2026
REST APIs are the backbone of modern web communication in 2026 used by every major tech company including Google, Twitter, Stripe, and Twilio. Whether you are applying for a Backend Developer, API Developer, Full-Stack Engineer, or Integration Specialist role, these top 10 REST API interview questions will help you prepare.
Keywords: REST API interview questions 2026, web services interview, RESTful API design, API authentication interview, HTTP methods interview
1. What is REST and what are its key principles?
REST (Representational State Transfer) is an architectural style for designing networked applications. Key principles include statelessness, client-server architecture, uniform interface, cacheability, layered system, and code on demand (optional). Resources are identified by URIs and manipulated through representations.
2. Explain HTTP methods and their usage in REST APIs.
GET retrieves resources (safe, idempotent). POST creates new resources. PUT updates/replaces entire resources (idempotent). PATCH partially updates resources. DELETE removes resources (idempotent). HEAD retrieves headers only. OPTIONS describes communication options. Use appropriate methods for semantic correctness.
3. What are HTTP status codes and when to use each?
2xx for success: 200 OK, 201 Created, 204 No Content. 3xx for redirection: 301 Moved, 304 Not Modified. 4xx for client errors: 400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 429 Too Many Requests. 5xx for server errors: 500 Internal Error, 503 Service Unavailable.
4. How do you implement authentication in REST APIs?
Common methods include API Keys (simple but less secure), JWT (JSON Web Tokens for stateless auth), OAuth 2.0 (delegated authorization), and Basic Auth (base64 encoded credentials). JWT is most popular with access tokens and refresh tokens. Always use HTTPS for secure transmission.
5. What is the difference between REST and GraphQL?
REST uses multiple endpoints with fixed data structures. GraphQL uses a single endpoint where clients specify exactly what data they need. REST can lead to over-fetching or under-fetching. GraphQL solves this but adds complexity. REST is simpler for CRUD operations. GraphQL excels with complex, nested data.
6. How do you version REST APIs?
Common strategies include URI versioning (/api/v1/users), query parameter (?version=1), header versioning (Accept: application/vnd.api.v1+json), and content negotiation. URI versioning is most common and explicit. Maintain backward compatibility and deprecate old versions with clear timelines.
7. Explain pagination, filtering, and sorting in REST APIs.
Pagination uses offset-based (?page=2&limit=20) or cursor-based approaches. Cursor-based is better for real-time data. Filtering uses query parameters (?status=active&role=admin). Sorting uses ?sort=created_at&order=desc. Include metadata like total count and next/previous links in responses.
8. What is CORS and how do you handle it?
CORS (Cross-Origin Resource Sharing) is a security mechanism that restricts cross-origin HTTP requests. Browsers send preflight OPTIONS requests for non-simple requests. Configure server with Access-Control-Allow-Origin, Allow-Methods, and Allow-Headers headers. Be specific rather than using wildcards in production.
9. How do you handle errors and validation in REST APIs?
Return consistent error response format with status code, error message, and error details. Validate input data at the API layer. Use appropriate HTTP status codes. Include field-level validation errors. Implement global error handling middleware. Log errors for debugging while returning user-friendly messages.
10. What are best practices for REST API design?
Use nouns for resource URIs, not verbs. Use plural names for collections. Implement HATEOAS for discoverability. Use proper HTTP methods and status codes. Version your APIs. Document with OpenAPI/Swagger. Implement rate limiting. Use compression. Support content negotiation. Follow consistent naming conventions.
Conclusion: REST APIs are fundamental to modern software development in 2026. Master HTTP methods, authentication, API design patterns, and best practices to ace your interviews.
Tags: #RESTAPI #InterviewQuestions #WebServices #APIDesign #Backend #HTTP #JWT #OAuth #APIInterview #REST2026