Question 1

How does it infer types from JSON?

Accepted Answer

It walks the parsed JSON and maps each value to a TypeScript type: strings, numbers and booleans become their primitives, objects become named interfaces, and arrays get their element type inferred.

Question 2

How are nested objects and arrays handled?

Accepted Answer

Nested objects are extracted into their own child interfaces named after the key. Arrays infer the element type by merging all items; arrays of objects produce a single shared interface.

Question 3

What happens with null or mixed types?

Accepted Answer

A null value becomes a union with null (for example string | null). When an array or property mixes types, a union of all observed types is generated. Empty arrays fall back to any[].

Question 4

When is a property marked optional?

Accepted Answer

When optional inference is on and a key is missing from some objects in the same array, it is emitted with a question mark (key?: type). Turn the option off to make every property required.

Question 5

Is my JSON uploaded anywhere?

Accepted Answer

No. Parsing and type generation run entirely in your browser; your JSON never leaves your device.

JSON to TypeScriptType Generator

JSON to TypeScript
Type Generator