graphql schema to typescript converter
typetools
instant, client-side type converter • 0ms network latency
export interface RootPayload {
id: string;
username: string;
email: string;
isActive: boolean;
score: number;
loginCount: number;
roles: string[];
}step-by-step integration guide
technical specification differences & end-to-end conversion workflow
Inverted Nullability Between GraphQL SDL and TypeScript Interfaces
One of the most frequent sources of runtime bugs in GraphQL-powered TypeScript applications stems from the inverted nullability model between the two languages. In TypeScript (with strictNullChecks enabled), interface properties are non-nullable by default unless explicitly marked optional (?) or unioned with null. In GraphQL SDL, the exact opposite is true: every field is nullable by default unless annotated with a trailing exclamation mark (!). Consequently, a GraphQL field declared as avatarUrl: String can resolve to null at runtime, and typing it naively as avatarUrl: string in TypeScript breaks compile-time type safety.
Compiling SDL Types, Enums, Unions, and Input Objects to TypeScript AST
Our GraphQL-to-TypeScript compiler parses raw SDL definitions—including type, input, interface, enum, and union blocks—and emits zero-dependency TypeScript types. Standard GraphQL scalars (ID, String, Int, Float, Boolean) are mapped to a customizable Scalars type dictionary so custom scalars (like DateTime or JSON) can be strongly typed. Every field lacking a GraphQL ! modifier is accurately typed as Maybe<T> (T | null | undefined), while non-null fields (String!) emit strict primitives (string). GraphQL list modifiers are preserved with exact precision: [String!]! compiles to Array<string>, whereas [String] compiles to Maybe<Array<Maybe<string>>>.
frequently asked questions
common developer questions answered
q:How does the converter translate GraphQL's non-null (!) modifier into TypeScript?
In GraphQL, fields without '!' are nullable by default. Our compiler maps fields with '!' (e.g., id: ID!) to strict TypeScript types (id: string), and fields without '!' (e.g., bio: String) to nullable unions (bio?: string | null).
q:How are GraphQL enums and unions represented in the TypeScript output?
GraphQL enums are compiled into idiomatic TypeScript string union types (or const enums) for zero runtime bundle size, and GraphQL union types are mapped directly to TypeScript discriminated union aliases.
q:Does the tool support GraphQL input types and query argument definitions?
Yes. Both GraphQL object types (type User) and input objects (input CreateUserInput) are parsed and emitted as dedicated TypeScript interfaces.