JSON to TypeScript Interface

Turning sample JSON into a TypeScript interface is one of the most common chores when integrating an API. You have a response example, you want compile-time safety, and manually transcribing twenty fields is error-prone. This tool walks the JSON tree once, inferring primitive types, extracting nested objects into their own interfaces, and unifying array element types.

Primitive inference is straightforward: numbers become `number`, strings become `string`, booleans become `boolean`, and `null` becomes `null`. Nested objects get promoted to named interfaces keyed by the parent property name — so a field called `profile` yields a `Profile` interface that the root references. Arrays unify their element types, so `[1, "x", 2]` becomes `(number | string)[]`.

A few caveats: the generator uses a single JSON sample, so optional fields are not detected. If a field can be absent, mark it with `?` manually. Very deep or recursive structures generate a long chain of interfaces; you may want to collapse some back into inline types for readability. Dates are treated as strings (ISO 8601), not `Date` objects — since JSON has no native date type, you must parse them yourself at the boundary.