GraphQL Schema Definition Reference
Reference for GraphQL schema language: types, interfaces, unions, enums, and directives.
Type System
GraphQL schemas define object types with fields, each having a type and optional arguments. Scalar types (Int, Float, String, Boolean, ID) are built-in; custom scalars can be declared. Interfaces define contracts that object types implement. Unions allow fields to return one of several types. Enums restrict fields to a set of named values. Input types structure mutation arguments.
- object type
- Fields with types
- interface
- Contract for objects
- union
- One of several types
type User { id: ID! }implements Nodeunion Result = User | ErrorSchema Elements
The Query, Mutation, and Subscription root types define entry points. Field arguments can have default values and be required (suffix !). List types use [Type] syntax. Directives (prefixed @) annotate fields for validation, caching, or deprecation. Schema directives can be custom-defined. The introspection system allows querying the schema itself. SDL (Schema Definition Language) is the human-readable format.
- root types
- Query, Mutation, Subscription
- !
- Non-null marker
- directives
- @-prefixed annotations
entry pointsrequired field/arg@deprecated, @cache