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

Paste a representative JSON sample and get TypeScript interfaces. Nested objects each become their own named interface, arrays become typed arrays, and mixed arrays produce a union element type.

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.