Question 1

What TypeScript types are generated?

Accepted Answer

The generator produces interface declarations matching the JSON structure. Strings become string, numbers become number, booleans become boolean, null becomes null, arrays become T[], and nested objects become nested interfaces. Fields that are null in the sample are typed as T | null.

Question 2

How does the generator handle arrays with mixed types?

Accepted Answer

If an array contains items of different types (e.g. [1, 'two', true]), the generated type is a union: (number | string | boolean)[]. For arrays with all-identical objects the element type is inferred from the first item.

Question 3

Are fields marked as optional?

Accepted Answer

Fields that are null in the sample JSON are generated as optional (?) or as T | null depending on the setting. If a key is missing from some objects in an array, it is also marked optional.

Question 4

Should I use interface or type for the generated output?

Accepted Answer

Both work for representing JSON shapes. interface is preferred for objects that may be extended (e.g. by intersection with other interfaces). type alias is preferred for unions and primitive aliases. The generator produces interface by default — you can rename it in your code.

Question 5

Is my JSON data safe to paste here?

Accepted Answer

Yes. Generation runs entirely in your browser. Nothing is sent to a server.

JSON → TypeScript

Generate TypeScript interfaces from JSON

JSON → TypeScript

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Generate TypeScript interfaces from JSON