Stop writing TypeScript interfaces by hand — convert JSON automatically

Source: Dev.to

How many times have you received a JSON response from an API and had to manually write TypeScript interfaces for it?

I built a free tool that does it instantly: JSON to TypeScript Converter.

Paste this JSON

{
  "id": 1,
  "name": "Alice",
  "email": "alice@example.com",
  "address": {
    "street": "123 Main St",
    "city": "Springfield",
    "zip": "62701"
  },
  "orders": [
    { "id": 101, "total": 29.99, "status": "shipped" }
  ]
}

Get this TypeScript

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

interface OrdersItem {
  id: number;
  total: number;
  status: string;
}

interface Root {
  id: number;
  name: string;
  email: string;
  address: Address;
  orders: OrdersItem[];
}

What the converter handles

• Nested objects – creates separate interfaces
• Arrays – infers element types
• Mixed types – e.g., string | number
• Null values – treated as unknown

Why I built it

I was developing SnapAPI – a tool that creates instant REST APIs from JSON – and kept needing to convert API responses to TypeScript. The converter emerged as a standalone utility.

Additional free tools

• JSON Formatter – beautify and minify JSON
• JSON Validator – real‑time syntax validation
• Fake Data Generator – generate realistic test data

All tools are free, require no signup, and are open source.