Question 1

How does it handle nested objects and arrays?

Accepted Answer

Each nested object is extracted into its own named interface, named after the field that holds it, and referenced from the parent. Arrays become element-typed arrays such as string[]; if an array mixes types, the element type becomes a union like (string | number)[]. Empty arrays are typed as unknown[] since no element is available to infer from.

Question 2

Why are some fields marked optional with a question mark?

Accepted Answer

The generator infers types from a single JSON sample, so it cannot know which fields are truly optional. As a practical heuristic, any field whose sample value is null is emitted as optional (field?: null). Review these against your real data — a field that is sometimes absent should be marked optional even if it was present in your sample.

Question 3

Is my JSON sent to a server?

Accepted Answer

No. Parsing and type generation run entirely in your browser with JavaScript. The JSON you paste never leaves your device, which makes the tool safe to use with API responses or payloads that contain sensitive data.

JSON to TypeScript

How Types Are Inferred

Frequently Asked Questions