JSON to TypeScript: Generate Interfaces and Types Online

Paste JSON and get TypeScript interfaces or types, with nested objects, optional fields and arrays handled. Runs in your browser.

Paste a JSON response and the tool writes TypeScript interfaces for it. Nested objects get their own interface, arrays are merged so a field missing from some items becomes optional, and mixed values become unions.

What it does

• Writes an interface (or type alias) for every nested object, named after its key.
• Merges all items of an array, so a field that is missing from some items becomes optional (?).
• Shows mixed values as unions, such as (number | string)[], and null as a type.
• Quotes keys that are not valid names, like "first-name".
• Open a .json file or paste text. Nothing is uploaded.

Example

{"id":1,"orders":[{"total":5},{"total":9,"note":null}]}

export interface Order {
  total: number;
  note?: null;
}

export interface Root {
  id: number;
  orders: Order[];
}

Frequently asked questions

Does it check the types of my real data?

It only looks at the sample you give it. If your API can return a field as a string sometimes and a number other times, include both in the sample so the union is created.

Why is a field optional?

It was missing from at least one item in an array. Fields that are present in every item stay required.

What happens to empty arrays?

An empty array has no items to learn from, so it becomes unknown[]. Put one real item in the sample to get a better type.

Is my JSON sent anywhere?

No. The conversion runs in your browser.

Runs in your browser. Nothing you type is sent to this site. Updated 2026-10-11.

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