Definition
GraphQL is a query language and API standard that lets clients request exactly the data they need from a server, rather than receiving a fixed, predetermined response shape.
Importance
With a traditional REST API, a client often receives more data than it needs, or has to make several separate requests to gather everything required for a single screen. GraphQL removes that inefficiency by letting the client specify precisely what it wants in a single request, which matters particularly for applications with complex, nested data or limited bandwidth, such as mobile apps.
Application
We use GraphQL where an application's data needs are complex or vary significantly between different parts of the interface, since it reduces both the number of requests and the amount of unnecessary data transferred compared with a traditional REST approach. This is a deliberate choice rather than a default, REST remains the simpler, more appropriate option for straightforward APIs, so we evaluate which standard actually fits a given application's data patterns rather than defaulting to whichever is more fashionable.
