JSON to TypeScript

This JSON to TypeScript converter writes the interfaces for a piece of JSON so you do not have to type them out field by field. Paste an API response, a config file or a fixture, and it produces a typed declaration for every object, works out which fields are optional by comparing array items, and turns mixed values into union types. Copy the result into your project and adjust names as needed.

Example

This response:

{
  "id": 42,
  "name": "Ayesha Khan",
  "address": { "city": "Lahore", "zip": "54000" },
  "orders": [
    { "id": 1001, "total": 49.99, "paidAt": "2025-04-02T10:15:00Z" },
    { "id": 1002, "total": 12.5, "paidAt": null, "coupon": "SPRING" }
  ]
}

gives:

export interface Root {
  id: number;
  name: string;
  address: Address;
  orders: Order[];
}

export interface Address {
  city: string;
  zip: string;
}

export interface Order {
  id: number;
  total: number;
  paidAt: string | null;
  coupon?: string;
}

coupon is optional because only one order has it, and paidAt is string | null because it is a string in one order and null in the other. The more varied the sample, the more accurate the types, so paste a response that includes the edge cases you know about.

How JSON Values Map to TypeScript

Options

• Root type name: the name of the top-level type. If the JSON is an array, this names the array type and its items get the singular form (Users and User).
• Declare as: interface or type aliases.
• export: adds export so the types can be imported from another file.
• All fields optional: marks every field with ?, useful for partial updates or loosely documented APIs.
• readonly: makes every field readonly, for data you do not mean to change.

Limits of Generating Types From a Sample

Generated types describe the JSON you pasted, not the API's contract. A field that is always present in your sample may be missing in other responses, a string that looks like an enum ("active", "paused") is typed as plain string, and numeric IDs that are sometimes strings will only show up as a union if the sample has both. Types also do not check data at runtime: if an API changes, TypeScript will not notice. Where the API publishes an OpenAPI or JSON Schema description, types generated from that are more reliable; this tool is ideal for undocumented APIs, quick scripts and fixtures.

Related Tools

If the JSON will not parse, the JSON formatter shows where the error is and can fix common mistakes. To look inside an auth token from the same API, use the JWT decoder, and to turn spreadsheet data into JSON first, the CSV to JSON converter.

Frequently Asked Questions