JSON to TypeScript

Generates TypeScript interfaces from a JSON sample. Nested objects become their own interfaces, arrays of records are merged so keys that appear in only some records are marked optional, and a field that is ever null is typed as a union with null. Paste a whole API response to type it in one step. Runs entirely in your browser — nothing is sent to a server.

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Generates TypeScript interfaces from a JSON sample. Nested objects become their own interfaces, arrays of records are merged so keys that appear in only some records are marked optional, and a field that is ever null is typed as a union with null. Paste a whole API response to type it in one step. Runs entirely in your browser — nothing is sent to a server.

Use cases

  • Typing an untyped API response without writing interfaces by hand
  • Turning a JSON fixture into types for a new client SDK

Examples

Nested object

{"id":1,"name":"Ada","tags":["math"],"address":{"city":"London"}}
export interface Root {
  id: number;
  name: string;
  tags: string[];
  address: Address;
}

export interface Address {
  city: string;
}

FAQ

Is my data sent to a server?

No — this tool runs entirely in your browser.

How are optional fields decided?

When the input is an array of objects, a key missing from any record is marked optional with "?". A key that is present but sometimes null is typed as a union with null instead.

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