GraphQL

GraphQL is an API query language and runtime in which clients request exactly the fields they want from a typed schema. A single endpoint accepts queries, mutations, and subscriptions, and the server resolves only the requested fields, often combining data from multiple underlying sources.

How it works

The server publishes a schema written in the GraphQL SDL, defining types, queries, mutations, and subscriptions. Clients send a query naming the operation, fields, and arguments. The server runs resolvers for each requested field and returns a JSON response shaped exactly like the query.

Key features include strong typing, introspection (the API documents itself), a single endpoint (no URL design needed), and the ability to coalesce many backends behind one schema.

Common implementations

• Server: Apollo Server, GraphQL Yoga, Mercurius, graphql-go, gqlgen, Strawberry
• Schema-first platforms: Hasura, PostGraphile, AWS AppSync, Grafbase
• Client: Apollo Client, urql, Relay, graphql-request
• Federation: Apollo Federation, Cosmo, Hot Chocolate, allowing multiple GraphQL services to expose one unified schema

GraphQL vs REST

• REST models resources, exposes many URLs, leans on HTTP caching, simpler to reason about.
• GraphQL models a graph of types, exposes one URL, gives clients flexible field selection, harder to cache, stronger fit when aggregating across multiple services.