Top 50 REST API Design Interview Questions & Answers (2026)

01 What is REST and what are its six architectural constraints? 02 What are the main HTTP methods used in REST APIs and what do they do? 03 What is idempotency and which HTTP methods are idempotent? 04 What are the most important HTTP status codes in REST APIs? 05 What are REST resource naming conventions? 06 What is the difference between path parameters and query parameters? 07 What are the most important HTTP request and response headers in REST APIs? 08 Why is JSON the standard response format for REST APIs? 09 How do you map CRUD operations to HTTP methods? 10 What does stateless design mean in REST? 11 What is an API endpoint? 12 What is the difference between HTTP and HTTPS? 13 What is Basic Authentication in REST APIs? 14 What is the difference between RESTful and non-RESTful APIs? 15 What is API documentation and what is Swagger/OpenAPI? 16 What is the Accept-Language header and how is it used? 17 What is a base URL and how should it be structured? 18 What is the difference between a collection resource and a singleton resource? 19 What is content negotiation in REST APIs? 20 What is a RESTful API's uniform interface constraint?

01 What is HATEOAS and how is it implemented? 02 What are the main API versioning strategies in REST and what are their tradeoffs? 03 What are the pagination strategies in REST APIs? 04 What is rate limiting and how is it communicated in REST APIs? 05 How does HTTP caching work in REST APIs with ETag and Cache-Control? 06 What are the OAuth 2.0 grant types and when do you use each? 07 What is JWT and how is it validated in REST APIs? 08 What is the difference between API keys and OAuth 2.0? 09 What is CORS and how does a preflight request work? 10 What is the RFC 7807 Problem Details format for REST API errors? 11 What is the difference between PUT and PATCH? 12 How do you handle long-running async operations in REST APIs? 13 What are the best practices for filtering, sorting, and searching in REST APIs? 14 What is an API gateway and what responsibilities does it handle? 15 How do webhooks work and what are the delivery guarantees? 16 What is an idempotency key for POST requests? 17 What is the OpenAPI 3.0 specification structure? 18 What are the best practices for designing API SDKs? 19 How do you design REST APIs for bulk operations? 20 What is sparse fieldsets and response compression in REST API performance?

01 What is the Richardson Maturity Model and what are its four levels? 02 How do you decide between REST, GraphQL, and gRPC for a new API? 03 What is consumer-driven contract testing with Pact? 04 What are backward compatibility strategies and Postel's Law in REST API evolution? 05 What is event-driven REST and when do you use webhooks vs SSE vs WebSockets? 06 How do you optimize REST API performance — N+1 avoidance, sparse fieldsets, and response compression? 07 What does an API governance and design review process look like at scale? 08 What is the REST API deprecation lifecycle management? 09 What are the security hardening measures for REST APIs — injection, mass assignment, BOLA/IDOR? 10 How do you design a REST API specifically for mobile-first clients considering bandwidth and offline-first use cases?