JSON to TypeScript

Generate TypeScript interfaces or type aliases from JSON.

JSON Input
TypeScript Output
TypeScript output appears here

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Frequently Asked Questions

Interface vs type — which should I pick?▾

Both describe the same shape. interface is more common for object shapes and supports declaration merging; type is more flexible for unions and computed types. Pick whichever matches your codebase's convention.

When does a field become optional?▾

A field is marked optional (with ?) when its sample value is null, since the tool infers from a single example rather than scanning every array element for presence.

What's the difference between unknown and any?▾

unknown is the type-safe choice — you must narrow it before using it. any opts out of type checking entirely. Prefer unknown unless you have a specific reason not to.

How are nested objects named?▾

Each nested object gets its own named interface/type derived from its key (PascalCased), so deeply nested JSON produces multiple readable declarations instead of one giant inline type.

Does array element type get inferred correctly?▾

The tool infers the array's element type from its first item. Arrays with mixed element shapes across items aren't merged into a union — keep sample arrays representative.