When a TypeScript app consumes an API, every response needs a type — and writing interfaces by hand from a sample response is tedious and error-prone: one mistyped field name and the compiler trusts a lie. Generating types from real JSON eliminates both the typing time and the typos.
This tool converts any JSON object or array into TypeScript interfaces, inferring types for nested objects, arrays, optional-looking fields, and primitives. Paste an API response, copy ready-to-use interfaces.
How to Use This Tool
- Paste a sample JSON response from your API.
- Interfaces are generated instantly, with nested objects extracted into named sub-interfaces.
- Rename the root interface to something meaningful (User, OrderResponse…).
- Paste the result into your .ts file and adjust optional fields as needed.
Frequently Asked Questions
How are nested objects handled?
Each distinct nested object becomes its own interface, referenced by the parent. An address object inside a user becomes interface Address, keeping the output readable and the types reusable.
What about fields that are sometimes null?
A single JSON sample cannot reveal optionality — if the sample has "middleName": null, the safest type is string | null, and fields absent in some responses should be marked optional with ?. Review generated types against your API documentation for fields that vary.
Why use interfaces instead of type aliases?
For object shapes they are nearly interchangeable. Interfaces give slightly better error messages, can be extended and merged, and are the convention in most codebases for API models — but converting the output to type aliases is purely stylistic.