GraphQL

Graph Query Language

Query language for APIs -- clients ask for exactly the fields they want.

When you'd see it: Modern API design, especially for apps with complex or varied data needs across web and mobile clients.

Why it matters: GraphQL lets a client request exactly the fields it needs in one query, avoiding the over- and under-fetching common with REST. The tradeoff is more server-side complexity and harder caching.

Common mistakes: Adopting GraphQL by default. For simple APIs it adds complexity REST would not, and its caching story is harder.