What is the difference between REST and GraphQL?
Why Interviewers Ask This
Foundational questions like this help interviewers calibrate the rest of the interview. A confident, accurate answer signals that you have solid System Design basics — a prerequisite for any developer role.
Answer
REST (Representational State Transfer) exposes data as resources with fixed URLs and HTTP methods. Each endpoint returns a predetermined data structure. Simple to understand, widely supported, good HTTP caching. Problems: over-fetching (endpoint returns more data than needed), under-fetching (multiple requests needed for related data), versioning complexity (/v1/, /v2/), rigid endpoint structure. GraphQL exposes a single endpoint where clients specify exactly what data they need via a query language. The server returns exactly what was requested — no more, no less. Key differences: Fetching: REST returns fixed data; GraphQL returns only requested fields; Multiple resources: REST needs multiple requests; GraphQL fetches all related data in one request; Versioning: REST often needs /v1/, /v2/; GraphQL adds fields and deprecates old ones without versioning; Type system: GraphQL has a strongly typed schema; REST has no built-in type system; Caching: REST is naturally cacheable via HTTP; GraphQL queries (POST) require custom caching (persisted queries, CDN with cache headers); Tooling: GraphQL has GraphiQL, introspection; REST has Swagger/OpenAPI. When to use GraphQL: complex data graphs, multiple client types (mobile/web) needing different data shapes, rapid product iteration. When to use REST: simple CRUD, public APIs, heavy caching requirements, limited client diversity. Many companies use both.
Common Mistake
Candidates often give textbook answers here. Interviewers are more impressed when you relate the concept to a specific problem you solved in a real System Design project.