JSON → types

How it works

Writing the types for an API response by hand is tedious and easy to get wrong. This tool infers them from a sample JSON document and generates code you can paste into your project.

Pick the language: TypeScript interfaces, Java records or Go structs. Every nested object becomes its own type, named after its key: address produces Address, and the elements of orders produce Order. Root name sets the name of the main type.

Types come from the values: strings, integers or decimals, booleans, arrays and null. If the JSON holds an array of objects, all its elements are combined, so fields missing from some of them become optional and fields that are sometimes null become nullable. In Go that means pointers with omitempty; in Java, wrapper types such as Long or Boolean.

Keys with dashes or spaces stay quoted in TypeScript, are mapped with the json:"…" tag in Go and with @JsonProperty in Java.

A single sample does not show every case: review the generated types before using them in production, especially fields that are null in your sample.

Examples

{"id": 7, "email": "ana@ejemplo.dev", "tags": ["admin"], "direccion": {"ciudad": "Santiago"}}

export interface Usuario {
  id: number;
  email: string;
  tags: string[];
  direccion: Direccion;
}

export interface Direccion {
  ciudad: string;
}

[{"id": 1, "total": 120}, {"id": 2, "total": 35.5, "cupon": "BIENVENIDA"}]

type Pedido []PedidoItem

type PedidoItem struct {
	ID    int64   `json:"id"`
	Total float64 `json:"total"`
	Cupon *string `json:"cupon,omitempty"`
}

Frequently asked questions