JSON to TypeScript Interface Generator

Worked example: an array of orders

{
  "orders": [
    { "id": 1, "total": 499, "coupon": "DIWALI10" },
    { "id": 2, "total": 1299 },
    { "id": 3, "total": 899, "note": null }
  ],
  "addresses": [{ "city": "Pune" }],
  "meta": {}
}

interface Root {
  orders: Order[];
  addresses: Address[];
  meta: Meta;
}

interface Meta {
  [key: string]: unknown;
}

interface Address {
  city: string;
}

interface Order {
  id: number;
  total: number;
  coupon?: string;
  note?: null;
}

The three orders are merged into one Order type. coupon and note appear in only some of them, so they are marked optional. Array fields are named after one element: orders gives Order, addresses gives Address. The empty meta object says nothing about its keys, so it accepts any key with an unknown value.

What to fix by hand afterwards

• Fields that were null in the sample get the type null, like note above. Replace it with the real type, such as string | null.
• Fixed sets of values come out as string. If status can only be "paid", "pending" or "refunded", write that union yourself.
• Dates in JSON are strings, so they stay string until your code turns them into Date objects.
• Empty arrays become unknown[], because there is no element to learn from.

Frequently Asked Questions