Generate TypeScript interfaces from a JSON sample, with nested types, optional keys and unions.
Runs in your browser — nothing you enter is sent to a server.
Paste a JSON sample — an API response, a config file — and the tool writes TypeScript declarations for it as you type. Each nested object becomes its own named interface, taken from its key in PascalCase, so address becomes Address and the items of orders become Order.
When an array holds several objects, their keys are merged: a key that only some items have becomes optional (qty?: number), and a key with different types becomes a union (string | number). Objects with the same shape share one interface. Choose type aliases if your code style prefers type over interface.
{"id":1,"address":{"city":"Paris"},"items":[{"sku":"A1","qty":2},{"sku":"B2"}]} gives an Address interface with city: string, an Item interface with sku: string and qty?: number, and a Root with items: Item[].
qty is optional because the second item doesn't have it.
[{"id":1},{"id":2,"note":null}] gives interface RootItem with id: number and note?: null, plus type Root = RootItem[].
The sample only had null for it, so the real type is unknown. Replace it with what the field holds when it's set, for example string | null. Paste a fuller sample to get better types.
No. TypeScript types disappear when the code is compiled. To check API responses at runtime, use a schema library such as Zod, or check the fields yourself.
Both describe object shapes equally well here. Interfaces can be extended and merged; type aliases can also name unions and primitives. Follow your project's style.
No. It is parsed and converted in your browser.
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