How does it know a field is optional?

When a JSON array has objects with different keys, any key that's missing from at least one element is marked optional in the generated type.

Does it detect enums automatically?

Yes — a string field that repeats 3 or more times with 5 or fewer distinct values (like a "status" or "role" column) is inferred as a string-literal union instead of a plain string.

Is the generated TypeScript guaranteed to actually compile?

The type inference is tested by feeding real JSON samples through the TypeScript compiler itself and asserting zero type errors, not just by eyeballing the output.

JSON to TypeScript

Types, Zod schemas and structs from any JSON.

Runs in your browser

Root name

JSON

TypeScript

export interface Address {
  city: string;
  zip: null;
}

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

JSON

Regex Tester

About

JSON to TypeScript infers a full type definition from any JSON document — walking nested objects and arrays, marking keys optional when they're missing from some array elements, merging mixed scalar types into unions, and recognizing a repeated low-cardinality string field (like a status column) as a literal-union "enum" automatically. The same inferred schema emits as TypeScript, a Zod schema, JSON Schema, Go structs, or Python dataclasses/Pydantic models — pick a target and the code updates live. Structurally identical nested objects are deduplicated into one named type instead of being repeated. Runs entirely in your browser; nothing you paste is sent anywhere.

Frequently asked

How does it know a field is optional?: When a JSON array has objects with different keys, any key that's missing from at least one element is marked optional in the generated type.
Does it detect enums automatically?: Yes — a string field that repeats 3 or more times with 5 or fewer distinct values (like a "status" or "role" column) is inferred as a string-literal union instead of a plain string.
Is the generated TypeScript guaranteed to actually compile?: The type inference is tested by feeding real JSON samples through the TypeScript compiler itself and asserting zero type errors, not just by eyeballing the output.