JSON to TypeScript Interface / Type Generator

A JSON to TypeScript generator that turns a JSON sample into clean TypeScript interfaces or type aliases, automatically handling nested objects, arrays, and unions.

This generator turns one realistic JSON response into clean TypeScript declarations for the whole shape, so the compile-time types always agree with what the server actually sends. APIs deliver JSON and TypeScript wants types, and the gap between the two is where a thousand hand-rolled interfaces get written — guessed from a response, wrong the moment a field is optional, and stale the day the payload changes. Copy the result into a types.ts, paste it into your API client layer, and let the compiler catch the mismatches for you.

The inference follows the data precisely. Every object becomes its own named interface (or type alias) with a PascalCase name built from its path — a profile object inside a User record becomes UserProfile — and identical shapes encountered in different places collapse into a single shared type instead of duplicating. Primitive values map to string, number and boolean; null appears literally as null; arrays of several element types become a union such as (string | number)[]; an empty array is typed unknown[] and an empty object Record<string, unknown>, both honest about the fact that a sample carries no information. Property keys that aren't valid identifiers — first name, age-in-years, a key starting with a digit — are quoted so the output stays valid TypeScript.

Two honest limits worth knowing. The types describe the JSON you pasted: if a field is genuinely optional in production, the sample had better show an object without it — paste a few representative records to capture the variation you actually see. And the tool generates the shape, not the final design: you'll still want to hand it to your team's TS conventions. Generation runs entirely in your browser — API responses, customer records and internal payloads never leave your machine, which is exactly what you want when deriving types from production data.