Top 30 Most Common Rest Api Interview Questions You Should Prepare For
What are the 30 REST API questions you should prepare for right now?
Concise answer: Focus on core concepts, HTTP mechanics, security, practical coding/testing, tools, and advanced design — below are 30 high-probability questions grouped by theme with quick answers you can adapt in interviews.
What is a REST API? — REST (Representational State Transfer) is an architectural style that uses stateless, resource-based interactions over HTTP. Example: each resource has a URI and standard methods (GET, POST, PUT, DELETE).
How is REST different from SOAP? — REST is lightweight, uses HTTP verbs and JSON, and is stateless; SOAP is protocol-heavy, uses XML, and defines its own standards.
What are REST principles? — Statelessness, layered system, client-server, uniform interface, cacheability, code-on-demand (optional).
What is a resource representation? — A resource is an abstract entity; representation (JSON/XML) carries its state between client and server.
What is HATEOAS? — Hypermedia as the Engine of Application State: responses include links so clients can discover actions.
When is REST not the best choice? — For real-time streaming, strict ACID transactions, or heavy operation-oriented APIs where RPC or gRPC may fit better.
Core Concepts (1–6)
What HTTP methods are used and why? — GET (read), POST (create), PUT (replace), PATCH (partial update), DELETE (remove), OPTIONS (discover allowed methods).
PUT vs PATCH — PUT replaces the entire resource; PATCH applies partial modifications. PUT is idempotent; PATCH might be non-idempotent unless designed so.
What are common status codes and meanings? — 200 OK, 201 Created, 204 No Content, 400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 409 Conflict, 500 Internal Server Error.
What is idempotency and why does it matter? — An operation is idempotent if repeated requests have the same effect as a single request (e.g., PUT, DELETE). It matters for retries and fault tolerance.
Can you send payloads in GET/DELETE? — Generally avoid payloads in GET; some servers accept bodies on DELETE but it's nonstandard and can break intermediaries.
How do you handle versioning? — URI versioning (/v1/users), header versioning (Accept header), or content negotiation; choose strategy for clarity and backward compatibility.
What is caching and cache-control? — HTTP caching reduces load: use Cache-Control headers, ETags, Last-Modified, and correct expiry settings.
HTTP Methods, Status Codes & Mechanics (7–13)
How to implement authentication? — Use tokens (JWT, OAuth2), API keys for service-to-service, or session cookies for browser clients. Prefer OAuth2 for delegated access.
How to authorize requests? — Implement role-based or attribute-based access control; validate tokens and scopes.
Common security vulnerabilities? — Broken authentication, injection, insecure direct object references, excessive data exposure, CORS misconfigurations.
Best practices for securing APIs? — Use HTTPS, validate input, rate-limit, use strong auth, sanitize outputs, monitor logs.
How to handle CORS? — Configure Access-Control-Allow-Origin, methods, headers server-side; only allow trusted origins.
Security & Authentication (14–18)
How to write a simple endpoint to list users? — Example: GET /users returns JSON array of user objects with pagination (limit, offset).
How to implement pagination and filtering? — Use offset/limit or cursor-based pagination; support query params for filtering and sorting.
How to implement caching? — CDN for static content, Cache-Control headers, ETag/If-None-Match for conditional requests.
How to test a REST API? — Unit tests, integration tests, contract tests (e.g., Pact), and tools like Postman, Rest Assured.
How to handle errors and error responses? — Use consistent error format with code, message, and possibly a trace id for debug (avoid leaking internals).
How to design request/response payloads? — Keep them minimal, versionable, and consistent (use snake_case or camelCase and document with examples).
How to implement rate limiting and throttling? — Use token buckets, API gateway policies, and return 429 Too Many Requests with Retry-After header.
Practical Coding & Testing (19–25)
What tools do you use to test REST APIs? — Postman, Curl, Rest Assured (Java), pytest + requests, SoapUI.
How is API testing different from UI testing? — API testing validates business logic, contracts, and integration points without UI flakiness; it's faster and more reliable for core functionality.
How to use Rest Assured (or similar) to set headers and assertions? — Build request with given(), set headers, perform method, and assert status and body with fluent API.
API Testing & Tools (26–28)
What is content negotiation? — Server selects response representation based on Accept header (JSON, XML) and returns appropriate Content-Type.
How to ensure backward compatibility? — Additive changes only (new fields optional), versioning, feature flags, and deprecation policies.
Advanced Design & Architecture (29–30)
Short takeaway: Master these 30 question areas with crisp, example-based answers and you’ll cover the vast majority of REST API interview ground.
(For source-aligned topic clusters and common interview patterns, see guides from Final Round AI and InterviewBit for core questions and expected answers.)
Sources: Final Round AI REST API Interview Questions, InterviewBit REST API interview questions
How do I explain core REST concepts clearly in an interview?
Concise answer: Define REST succinctly, mention its key constraints, give a short example, and relate it to the job’s context.
Expand: Start with one‑sentence definition: "REST is an architectural style that models services as stateless resources accessed via HTTP." Then enumerate the most interview-relevant constraints: client-server separation (decouples UI from backend), statelessness (each request contains all info), cacheability (improves scalability), uniform interface (standardizes interactions), layered system, and optional code-on-demand. Briefly contrast with SOAP or RPC when asked about alternatives. Use a real-life example: "GET /orders/123 returns a JSON representation of order 123; to update status use PATCH /orders/123 with {status:'shipped'}."
Tip: If asked about HATEOAS, explain the practical trade-offs — it's RESTful but increases payload complexity and isn’t always adopted in public APIs.
Takeaway: Give a crisp definition, list core constraints, and show a concrete request/response example to signal practical understanding.
(Supporting reading: Final Round AI covers core concepts well.)
How should I answer questions about HTTP methods, status codes, and versioning?
Concise answer: Name methods and typical uses, show understanding of idempotency and response codes, then explain a pragmatic versioning strategy.
Expand: In interviews, say: GET is safe and idempotent (read-only), POST creates, PUT replaces (idempotent), PATCH updates partially, DELETE deletes, OPTIONS discovers methods. Explain status codes grouped by class (2xx success, 4xx client errors, 5xx server errors) and give examples like 201 for created resources and 409 for conflicts (e.g., duplicate key). Demonstrate idempotency knowledge: retries matter — design operations accordingly.
For versioning, state trade-offs: URI versioning (/v2/resource) is explicit and cache-friendly; header or media-type versioning keeps URIs clean but is harder to route. Choose based on client control and backward compatibility needs.
Example answer snippet: "I prefer URI versioning for public APIs because it's explicit and easy for clients and proxies, while using semantic versioning in documentation."
Takeaway: Show both theoretical correctness and pragmatic trade-offs — interviewers value practical choices.
(See Turing’s REST API interview guidance for method and versioning examples: Turing REST API questions.)
How do I explain authentication and security best practices for REST APIs?
Concise answer: Focus on strong transport security (HTTPS), robust authentication (OAuth2/JWT where appropriate), careful authorization, and defense-in-depth.
API keys: simple, good for service-to-service but limited for user delegation.
JWT: stateless tokens containing claims, good for scaling, but be careful with secrets and token revocation.
OAuth2: standard for delegated access (authorization code flow, client credentials flow for services).
Expand: Start with HTTPS to protect transport. For authentication describe usual choices:
Discuss authorization patterns: role-based access control (RBAC) or attribute-based (ABAC), and always validate token scopes. Cover common vulnerabilities (injection, insufficient logging, broken object-level authorization) and mitigations: input validation, least privilege, logging, rate limiting, and secrets management. For CORS, explain server-side header configuration and the risk of overly permissive Access-Control-Allow-Origin.
Example interview phrasing: "I implement OAuth2 for user delegation, secure tokens with short lifetimes and refresh tokens, and enforce scope checks on each endpoint."
Takeaway: Combine policy (who can do what), transport security, token management, and monitoring to demonstrate holistic security thinking.
(Practical security examples and testing approaches are covered by Final Round AI and GeeksforGeeks.)
Sources: Final Round AI, GeeksforGeeks API Testing
How do I demonstrate coding and practical REST implementation skills in interviews?
Concise answer: Walk through a small, well-structured example, include error handling and tests, and keep performance concerns in mind (pagination, caching).
Path: GET /users?limit=25&cursor=ey...
Response: {data: [...], nextCursor: "...", total: 123}
Expand: When presented with a coding prompt, choose clear endpoints and show request/response shapes. Example: implementing GET /users with pagination:
Discuss validations, error responses (400 for invalid input, 404 for not found), and idempotency considerations on update endpoints. If asked about caches, explain ETag/If-None-Match and server-side caching strategies. For testing, mention unit tests for business logic, integration tests against an in-memory DB, and contract tests for client-server agreements.
If you must write code, prefer clarity over cleverness: brief controller, service, and data access layers with comments about handling concurrency and transactions.
Takeaway: Show end-to-end thinking — from endpoints and payloads to testing and operational concerns.
(See practical examples and testing tool references at Frugal Testing and Final Round AI.)
Sources: Frugal Testing Rest Assured guide, Final Round AI
Which API testing tools and approaches should I mention in interviews?
Concise answer: Name common tools (Postman, Rest Assured, Postman/Newman, Curl, pytest + requests), explain when to use each, and describe test layers: unit, integration, contract, and end-to-end.
Unit tests: business logic in isolation.
Integration tests: endpoints with DB/stubs.
Contract tests: enforce API schema with clients.
Load tests: validate performance under stress.
Expand: For manual exploratory testing use Postman or Curl; for automated tests use Rest Assured (Java), pytest with requests (Python), or k6 for load testing. Mention contract testing (Pact) for consumer-driven API contracts. Describe test types:
Show a short example: "With Rest Assured you build a request with given(), set headers, call POST, then assert status and body fields." Also emphasize CI integration: run automated API tests in CI pipelines and fail builds on contract drift.
Takeaway: Demonstrate familiarity with a toolchain and a layered testing strategy rather than just a single tool.
(For detailed Rest Assured examples see Frugal Testing and GeeksforGeeks.)
Sources: Frugal Testing, GeeksforGeeks API Testing
How do I answer advanced REST design questions like idempotency, HATEOAS, and content negotiation?
Concise answer: Define the term, explain practical pros and cons, and give a real-world trade-off based on system needs.
Expand: For idempotency, define it (repeated same request leaves state unchanged) and show how to implement idempotency keys for POST to safely retry payments. For HATEOAS, explain it enables discoverability but can increase payload size and complexity; many APIs choose simple hypermedia links or omit HATEOAS for public APIs. For content negotiation, explain Accept/Content-Type headers and how servers choose representation; highlight when multiple formats are truly needed.
When discussing backward compatibility, explain strategies: additive changes only (new optional fields), deprecation headers, semantic versioning, and feature flags to roll out changes.
Takeaway: Interviewers look for nuanced trade-offs — explain both the ideal and the pragmatic approach for real systems.
(Sources that cover advanced topics include Final Round AI and community design guides like GitHub collections.)
Source: Final Round AI
How should I structure answers to behavioral API design questions during onsite interviews?
Concise answer: Use a structured format (context, decision, trade-offs, outcome) and support your answer with a short diagram or example.
Expand: Start with the problem context: user needs, scale, and constraints (e.g., mobile clients, low latency). Then state the design decision (e.g., choose cursor pagination) and explain why: performance benefits, consistency, and client experience. Discuss alternatives and trade-offs (offset pagination simplicity vs. cursor pagination performance). Finish with an outcome or metric if possible (reduced latency, improved throughput).
You can use STAR or CAR frameworks for behavioral responses to show impact: Situation, Task, Action, Result (STAR) or Context, Action, Result (CAR).
Takeaway: Combine technical rationale with business impact and use a repeatable answer structure to stay clear under pressure.
How Verve AI Interview Copilot Can Help You With This
Verve AI acts as your quiet co-pilot during interviews — analyzing context from the question, suggesting concise STAR/CAR structured phrasing, and helping you stay calm and articulate. It gives real-time examples, converts your draft answers into clear responses, and offers code snippets and follow-up talking points tailored to the role. Verve AI helps you adapt explanations for different seniority levels and quickly recall best-practice patterns like idempotency, caching, and OAuth2. Try Verve AI Interview Copilot to practice these answers confidently.
(Note: This tool monitors the conversation context and nudges phrasing, not the interviewer.)
What Are the Most Common Questions About This Topic
Q: What is REST?
A: REST is an architectural style using stateless HTTP resources and standard verbs.
Q: Difference between PUT and PATCH?
A: PUT replaces a resource; PATCH applies partial updates.
Q: Best auth method for public APIs?
A: OAuth2 for delegated user access; API keys for simple service auth.
Q: How to test APIs in CI?
A: Run unit, integration, and contract tests (Postman/Newman or Rest Assured) in CI.
Q: What is idempotency?
A: An operation that can be repeated with the same result as one execution.
Q: When to use HATEOAS?
A: For complex hypermedia-driven systems; skip for simple CRUD APIs.
Quick sample answers you can memorize (bite-sized)
"REST is stateless and resource-based; use URIs to represent resources and HTTP verbs for actions."
"PUT is idempotent and replaces a resource; PATCH is for partial updates."
"I secure APIs with HTTPS, OAuth2 for user auth, short-lived JWTs, and scope-based authorization."
"For pagination I prefer cursor-based for large datasets; offset is ok for small ones."
"I test with unit tests, integration tests, and contract tests; Postman/Newman or Rest Assured integrate well into CI."
Interview prep checklist: practical steps to get ready
Review the top 30 questions above and craft short (30–90 second) answers.
Prepare one or two code snippets for common tasks (list, create, update).
Practice explaining design trade-offs for pagination, versioning, and caching.
Run through security scenarios (token revocation, rate-limiting, CORS).
Set up Postman collections or Rest Assured test examples to demonstrate automated testing.
(For curated question sets and sample answers see InterviewBit and Final Round AI.)
Sources: InterviewBit REST questions, Final Round AI
Conclusion
Recap: Prioritize clear definitions, practical examples, and trade-offs across core concepts, HTTP mechanics, security, testing, and advanced design. Structure answers using STAR/CAR, include concise code or payload examples, and practice aloud. Preparation and a few concrete examples will make your answers confident and persuasive. Try Verve AI Interview Copilot to rehearse answers, get context-aware phrasing, and feel prepared for every REST API interview.