JSON to TypeScript

TypeScript catches mistakes before they reach production, but only if your data is typed. When you call an API, you need interfaces that describe the response. Writing them by hand for large payloads is tedious. This tool generates TypeScript interfaces from a sample JSON payload, recursively handling nested objects and arrays.

How to use it

1. Paste a representative JSON response.
2. Copy the generated interfaces into your project.
3. Rename the root interface and refine types the sample could not reveal.

Example

Input (double quotes in real JSON):

{ 'id': 7, 'name': 'Asha', 'email': null, 'roles': ['admin'], 'profile': { 'city': 'Pune', 'age': 31 } }

Output:

interface Root {
  id: number;
  name: string;
  email: null;
  roles: string[];
  profile: Profile;
}

interface Profile {
  city: string;
  age: number;
}

Refine after generating

• Null values: a field that is null in the sample is typed as null. Change it to the real type plus null, such as email: string | null.
• Optional fields: mark fields that are not always present with ?.
• Union and literal types: a status that can only be 'active' or 'banned' is better typed as a union than as string.
• Empty arrays give no item type; fill it in.
• Dates arrive as strings in JSON; keep them as string until you parse them.

Types are not validation

Interfaces disappear at runtime, so a server can still send unexpected data. For untrusted input, validate with a schema library such as Zod or Valibot and infer the TypeScript type from the schema.