GraphQL is a query language for APIs and a runtime for fulfilling those queries with your existing data. GraphQL provides a complete and understandable description of the data in your API, gives clients the power to ask for exactly what they need and nothing more, makes it easier to evolve APIs over time, and enables powerful developer tools.
GraphQL queries access not just the properties of one resource but also smoothly follow references between them. While typical REST APIs require loading from multiple URLs, GraphQL APIs get all the data your app needs in a single request. Apps using GraphQL can be quick even on slow mobile network connections.
GraphQL is a query language for your API, and a server-side runtime for executing queries using a type system you define for your data. GraphQL isn’t tied to any specific database or storage engine and is instead backed by your existing code and data.
A GraphQL service is created by defining types and fields on those types, then providing functions for each field on each type. After a GraphQL service is running (typically at a URL on a web service), it can receive GraphQL queries to validate and execute. The service first checks a query to ensure it only refers to the types and fields defined, and then runs the provided functions to produce a result.
