JSON to TypeScript

Generating TypeScript interfaces from JSON

This tool reads a sample JSON object and emits TypeScript type definitions that describe its shape. Instead of hand-writing an interface for a 40-field API response, you paste one real payload and get interface declarations with inferred field types. It is a huge time saver when you are integrating against an API that has no published types.

How inference works

The generator walks the JSON tree. A string becomes string, a number becomes number, nested objects become their own named interfaces, and arrays become T[] based on their first element. The output is only as good as the sample: a field that is null in your example cannot be inferred, and an array that happens to be empty gives the tool nothing to work with.

Example

Input JSON:

{ "id": 7, "name": "Ada", "tags": ["x"], "active": true }

Generated interface:

interface Root {
  id: number;
  name: string;
  tags: string[];
  active: boolean;
}

FAQ

What about optional or nullable fields? One sample cannot tell the difference between "always present" and "sometimes missing". Review the output and mark fields with ? or union them with null where your API actually allows it.

Does it handle mixed-type arrays? An array like [1, "a"] ideally becomes (number | string)[], but simpler tools pick only the first element, so check the result.

Can I trust this for runtime safety? No. Generated types describe a shape at compile time only. For validated parsing, pair the interface with a schema library and your JSON formatter for inspecting the raw payload.