JSON to TypeScript Converter

About this tool

Paste a JSON sample and get TypeScript type definitions you can use immediately. Emits `interface` declarations. Optional fields use `?`, so `strictNullChecks` will catch the ones your API omits.

When you would use it

• Typing an API client or validating a response shape at the boundary
• Bootstrapping models from a real JSON response instead of writing them by hand
• Keeping types in step with an API that has changed

Worked example

{
  "id": 4815,
  "name": "Ada Lovelace",
  "active": true,
  "score": 91.5,
  "roles": ["admin", "editor"],
  "address": { "city": "London", "postcode": "NW1" }
}

export interface Root {
  id: number;
  name: string;
  active: boolean;
  score: number;
  roles: string[];
  address: Address;
}
export interface Address {
  city: string;
  postcode: string;
}

Things worth knowing

• Every object in an array is merged when inferring the shape, so a field missing from one item is marked optional rather than assumed to always be present.
• Identical nested shapes are de-duplicated into a single type instead of generating near-duplicates.
• Array element types are named from the singular of the field name, so posts produces a Post type.
• A sample with more records produces better types, because optional fields only reveal themselves across several examples.