GraphQL overview

GraphQL is a query language for APIs and a runtime for executing those queries, developed by Facebook in 2012 and open-sourced in 2015. It lets clients specify exactly the data they need, eliminating over-fetching and under-fetching that plague REST APIs. The GraphQL SDL (Schema Definition Language) defines types, queries, mutations, and subscriptions. Server implementations include Apollo Server, Yoga, Hasura, and Strawberry (Python). Client tooling includes Apollo Client, urql, and URQL. Features like persisted queries, DataLoader for batching, and schema stitching/federation (Apollo Federation) are common patterns at scale. Closely related to REST API design and used heavily in frontend-heavy web and mobile applications.