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GraphQL

A query language for APIs — clients describe exactly what data they need. Single endpoint, typed schema, no over/under-fetching. Created by Facebook. More flexible than REST but adds complexity (schema, resolvers, caching).

Created by

Lee Byron, Nick Schrock, Dan Schafer · Created GraphQL at Facebook in 2012

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When to use
  • Complex frontends with varied data needs.
  • Mobile apps (bandwidth-sensitive).
  • When clients need flexible queries.
  • Microservices federation.
When not to
  • Simple CRUD (REST is simpler).
  • When caching is critical (REST is easier).
  • When team doesn't know GraphQL.

Definition

GraphQL is a query language for APIs. Schema defines types and fields. Clients send queries describing what they need; resolvers fetch the data. Single endpoint (POST /graphql). Introspection lets tools explore the API. Subscriptions for real-time.

Why it exists

returns fixed response shapes — over-fetching (too much data) and under-fetching (multiple requests). GraphQL lets clients specify exactly what they need in one query.

How it works

Define a schema (types, fields, resolvers). Client sends a query: { user(id: 1) { name, posts { title } } }. Server validates against schema, resolvers fetch fields, returns JSON matching the query shape. Apollo Server/Client are popular.

Scaling limits

Complexity (schema, resolvers, codegen). Caching is harder than . N+1 query problems (use DataLoader). DoS surface (clients can craft expensive queries — need cost analysis).

Cost shape

Free and open source. Apollo has paid tiers for federation/features.

Alternatives

  • REST — Simpler, cacheable, less flexible.
  • tRPC — Type-safe, TS-only, no schema.
  • gRPC — Internal APIs, binary, typed.

Failure modes

  • N+1 queries.
  • Complexity.
  • Caching difficulty.
  • DoS from expensive queries.

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