JSON to TypeScript

Type inference from a sample is a small job that most converters overstate. This one reads exactly the JSON you paste and nothing else: the root object becomes one export interface, and every object nested inside it becomes its own named interface, named for the path that reached it — User, then UserProfile, then UserProfileAddress — so the output is a set of flat declarations you can read top to bottom instead of a wall of inline nested types. The old version of this page finished every object document with export type User = User;, which is TS2300 Duplicate identifier and does not compile at all. There is no such line here, and nothing is labelled Generated until the emitted names have been checked for duplicates and for resolution.

The decisions it makes are the ones a sample can actually support, and they are stated rather than buried. An array of objects is merged into a single element shape: a key missing from at least one element is marked optional, and keys whose shapes disagree become a union of what was really seen, never any. A JSON null is a value rather than a hole, so it stays required and renders as null — an earlier version made it any, which quietly turned a required field into an optional one. Every number is number; a date, a UUID or an enum that arrives as a string reads as string, because nothing in a sample can tell those apart. An empty object is Record<string, never> and an empty array is unknown[], since a member-less interface would accept every object you could pass it. A root name that is a TypeScript keyword, or a built-in type such as Record that an interface would shadow, falls back to Root and the page says so out loud instead of substituting quietly.

What it deliberately does not do is worth the same space as what it does. There is no JSDoc on each field, because a comment guessed from one value is a comment that will be wrong. There is no enums, no generics, no type-alias mode, no converters, and no date library. A key your sample does not contain is not marked optional, because the sample cannot know whether the field is absent, null, or simply not in the response you happened to paste. Copy the result into a .ts file and it compiles as written; widen the sample, or edit the interface, before you rely on it.

Input is capped before anything is parsed — 200,000 characters of pasted text, 64 nesting levels, 200,000 values in the document, and 400,000 characters of generated code, since an array of objects can imply more fields than the input has characters — and each cap is refused with the real numbers rather than silently truncating. Your JSON is read in this tab. Nothing is uploaded, and no request is made with your data at all.