JSON to TypeScript

It reads a JSON sample and generates matching TypeScript interfaces (or type aliases). It walks every object, names nested objects in PascalCase from their keys, infers array element types as T[], and maps primitives to string, number, boolean and null — giving you ready-to-paste types.

Each nested object becomes its own interface, named from its key in PascalCase. Arrays are typed from their items as T[]: an array of objects reuses that item interface, an empty array becomes any[], and a mixed array becomes a union such as (string | number)[].

Both describe the same shape. An interface is declared with interface Name { ... } and can be extended or merged, while a type alias uses type Name = { ... }. Pick whichever matches your codebase style — the generated fields are identical.

When enabled, any key whose value is null in the sample is emitted as an optional property with a ? (for example name?: null). It is handy when null simply means the field may be missing. Leave it off to keep every property required.

No. Parsing and generation run entirely in your browser — your JSON is never uploaded to a server and nothing is stored. It is safe for sample payloads you would not want to transmit.

The input must be valid JSON: keys and strings in double quotes, no trailing commas, and no comments. The error message shows what the browser parser rejected — fix that spot, or paste a real response, and the TypeScript regenerates live.