JSON → TypeScript is a free data & format tool that runs entirely in your browser — generate interfaces from sample JSON. No upload, no account, no limits.
Generate TypeScript interfaces from a sample JSON object or array. Nested objects become their own named interfaces, arrays infer their element type, and mixed-type arrays become unions — giving you a typed starting point in seconds.
Types are inferred from one example, so optional or nullable fields may need a quick manual tweak.
Each becomes its own interface, named after the key, and referenced from the parent.
Element types are unified into a union (e.g. (string | number)[]).
Every calculation happens on this page, in your own browser. Your input is never sent to a server, never logged and never used for training — which also means the tool keeps working when you are offline.