How are nested objects and arrays typed?

Nested objects each get their own named interface based on the PascalCased property key, and arrays become T[]. When an array mixes types, the element type becomes a union such as (number | string)[].

How accurate are the generated types?

Types are inferred from a single sample, so they reflect exactly what's in that sample. Fields that are optional or only appear in other records won't show up, and a null value is typed as null and marked optional. Treat the output as a strong starting point to refine.

Is my JSON uploaded anywhere?

No. The inference runs entirely in your browser with JavaScript — your data is never sent to a server or stored.

JSON to TypeScript Interface

Generate TypeScript interfaces from JSON

Writing TypeScript interfaces to match an API response by hand is tedious and easy to get wrong. Paste a representative JSON sample and this tool infers the matching TypeScript interfaces for you, ready to drop into your project.

How it works

The generator walks the sample and types each value, naming a fresh interface for every nested object after its PascalCased key:

JSON	TypeScript
string	`string`
number	`number`
boolean	`boolean`
null	`null` (field marked optional)
object	its own named interface
array of T	`T[]`
mixed array	union, e.g. `(number \| string)[]`

Example

This JSON:

{ "id": 7, "user": { "name": "Sam" }, "tags": ["a", "b"] }

generates:

interface Root {
  id: number;
  user: User;
  tags: string[];
}

interface User {
  name: string;
}

Because the types are inferred from one sample, they reflect exactly what’s in that sample — fields that are optional or absent won’t appear, so treat the output as a strong starting point. All inference happens in your browser — your data is never uploaded or stored.