# Top 50 REST API & Web Services Interview Questions & Answers (2026) > Canonical Source: https://ratemyinterview.online/blog/top-50-rest-api-interview-questions-2026 > Platform: RateMyInterview (https://ratemyinterview.online) — Voice AI Mock Technical Interview Platform > Practice Live Out Loud: https://ratemyinterview.online/practice (2 free full sessions included, zero credit card required) Web Services & APIs · 2026 # Top 50 REST API & Web Services Interview Questions & Answers (2026) August 24, 2026 · 20 min read · RateMyInterview Backend Architecture Team ## Key Takeaways — REST API Interviews in 2026 - • **Core Architectural Constraints:** A truly RESTful API adheres to 6 Roy Fielding constraints: Client-Server, Statelessness, Cacheability, Layered System, Uniform Interface (HATEOAS), and Code-on-Demand. - • **HTTP Methods & Idempotency:** `GET, PUT, DELETE, HEAD, OPTIONS` are idempotent (multiple identical requests have the exact same side-effect). `POST` is NOT idempotent. `PATCH` is partially idempotent. - • **HTTP Status Code Precision:** Distinguish `401 Unauthorized` (missing/invalid credentials) vs `403 Forbidden` (authenticated but lacking permissions), and `200 OK` vs `201 Created` vs `204 No Content`. - • **API Security & Rate Limiting:** JWT refresh token rotation, OAuth 2.1 authorization code flow with PKCE, CORS headers, and Token Bucket algorithm rate limiting. ## Table of Contents - [1. REST Principles & Architectural Constraints](#rest-principles) - [2. HTTP Methods & Idempotency Explained](#http-methods-idempotency) - [3. Essential HTTP Status Codes Cheat Sheet](#http-status-codes) - [4. REST vs GraphQL vs gRPC: When to Use What](#rest-vs-graphql-grpc) - [5. API Security: JWT, OAuth2, CORS & Rate Limiting](#api-security-design) - [6. Frequently Asked REST API Interview Questions](#rest-api-faqs) ## 1. REST Principles & Architectural Constraints REST stands for **Representational State Transfer**, an architectural style designed by Roy Fielding in 2000. #### 1. Statelessness Every request from the client must contain all information needed to process it. No session state is stored on the server. #### 2. Uniform Interface (HATEOAS) Resources are uniquely identified via URIs, manipulated through representations (JSON/XML), and include hypermedia links for state transitions. #### 3. Cacheability Responses must explicitly define whether they are cacheable using headers like `Cache-Control` and `ETag`. #### 4. Layered System Clients cannot tell whether they are connected directly to the end server or an intermediary like a proxy or load balancer. ## 2. HTTP Methods & Idempotency Explained **Idempotency** means making the same request N times yields the exact same server-side resource state as making it once. Method Purpose Safe? Idempotent? GET Retrieve representation of a resource YES YES POST Create a new subordinate resource NO NO (creates duplicates) PUT Replace full resource / create at known URI NO YES PATCH Partially modify fields of a resource NO CONDITIONAL DELETE Remove resource identified by URI NO YES ## 3. Essential HTTP Status Codes Cheat Sheet - **200 OK:** Standard success response for GET, PUT, PATCH. - **201 Created:** Resource successfully created via POST (includes `Location` header). - **204 No Content:** Action successful, no body returned (common for DELETE). - **400 Bad Request:** Malformed JSON or validation errors. - **401 Unauthorized:** Authentication credentials missing or invalid. - **403 Forbidden:** Authenticated successfully, but client lacks permission. - **404 Not Found:** Resource URI does not exist. - **409 Conflict:** Request conflicts with current resource state (e.g. duplicate email). - **429 Too Many Requests:** Rate limit exceeded. - **500 Internal Server Error:** Unhandled runtime exception on server. - **503 Service Unavailable:** Server overloaded or undergoing maintenance. ## 4. REST vs GraphQL vs gRPC: When to Use What Protocol Strengths Best For REST Universal HTTP standard, cacheable at CDN level, simple debugging Public APIs, third-party integrations, CRUD services GraphQL Prevents over/under-fetching, single endpoint, client-defined schemas Complex frontend apps, dashboards, mobile backends (BFF) gRPC HTTP/2 binary serialization (Protobuf), ultra-low latency, bidirectional streaming Internal microservice-to-microservice communication ## 5. API Security: JWT, OAuth2, CORS & Rate Limiting #### Authentication & Authorization (JWT vs OAuth2) OAuth2 handles delegated access authorization. JSON Web Tokens (JWT) act as stateless cryptographically signed bearer tokens carrying user claims. #### CORS & Rate Limiting Defenses Restrict allowed origins via explicit `Access-Control-Allow-Origin` headers and throttle abusive requests using Token Bucket algorithms in Redis. ### Practice REST API & Backend Mock Interviews Simulate voice-based backend engineering and API design technical interviews with Sophia AI. Instant real-time feedback on architecture, security, and status codes. [ Full Stack Mock Interview ](/practice/full-stack-developer-mock-interview) [ Node.js API Mock ](/practice/node-mock-interview) ## 6. Frequently Asked REST API Interview Questions What is the difference between PUT and PATCH? `PUT` is used for full resource replacement — you must send all fields of the resource. Any omitted fields may be nullified. `PATCH` is used for partial modification — you only send the specific fields you wish to update. How do you implement Rate Limiting for a REST API? Commonly implemented at the API Gateway or middleware layer using Redis with the **Token Bucket** or **Sliding Window Log** algorithm. The server returns headers like `X-RateLimit-Limit`, `X-RateLimit-Remaining`, and `Retry-After` with HTTP 429 when limits are breached. --- ### Practice Live with Sophia AI Practice realistic voice technical interviews tailored directly to your real resume at https://ratemyinterview.online. Sophia AI speaks and listens via your microphone with sub-second speech latency (~900ms), giving instant objective scores, full transcripts, and question-by-question model solutions.