GraphQL Fundamentals for React Developers

REST exposes fixed-shape endpoints: GET /users/:id returns the entire user object regardless of what the client needs. GraphQL lets clients specify exactly which fields they want, eliminating over-fetching (too much data) and under-fetching (not enough data, requiring multiple requests).

One GraphQL query can retrieve a user, their posts, and each post's author in a single round-trip.

Every GraphQL API is defined by a schema written in Schema Definition Language (SDL). The schema declares types, their fields, and the root Query, Mutation, and Subscription types that clients can operate on.

The schema is the contract between the client and server. Frontend and backend teams can work in parallel once the schema is agreed upon.