JSON to TypeScript interfaces

No. The conversion runs entirely in your browser. The file never leaves your device – there is no server that could see it. Once the page has loaded, the tool even works offline.

All elements of an array are merged into one interface. A key that only some elements have becomes optional (“name?: string”); a key with different types becomes a union (“id: number | string”). The element type is named after the property in singular: “users” gives “User”.

JSON often contains maps keyed by data, for example {"2026-08-24": {…}, "2026-08-25": {…}}. One interface field per date would be useless, so such objects become Record<string, T> when the option is on. Switch it off to always get interfaces.

An empty array or a value that is only ever null carries no type information, so the generator writes unknown[] or null. Replace it by hand once you know what the field holds – the rest of the code is ready to use.