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Online JSON to TypeScript Interface Generator

Transform raw JSON payloads into clean, idiomatic TypeScript declarations. Nested objects are automatically extracted into distinct, reusable interfaces, array items are type-inferred with union support, and missing keys across array records are cleanly tagged with optional modifiers.

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#How to Use This Tool

1Paste your JSON payload or API response into the left editor pane.
2Customize the root type name (default: "Root") and export style (interface vs. type alias).
3View the generated TypeScript declarations in the right pane in real time.
4Copy to clipboard or share code state via a privacy-preserving compressed hash URL.

#Mathematical Formula & Standards

Type mapping semantics: JSON String -> string; JSON Number (integer or float) -> number; JSON Boolean -> boolean; JSON Null -> null; JSON Array -> T[] or (T1 | T2)[]; JSON Object -> Extracted named Interface. The conversion algorithm operates linearly O(N) over the AST representation inside an isolated background Web Worker thread, preventing UI lockups on multi-megabyte payloads.

#Edge Cases & Technical Considerations

Heterogeneous Array Element Unions

When an array contains mixed types (e.g. [1, "hello", true]), the engine infers a consolidated union type: (string | number | boolean)[].

Special Characters and Reserved Identifier Keys

Property names containing hyphens, spaces, or leading digits (e.g. "x-api-key", "123code") are automatically wrapped in quotes to produce syntactically valid TypeScript.

Optional Field Detection Across Array Records

When parsing an array of objects where certain keys appear only in a subset of items, the engine automatically flags those properties as optional (key?: type).

#Frequently Asked Questions

Q:Does my JSON data get uploaded to an external server?

No. The AST parser and TypeScript generator run 100% locally inside a dedicated Web Worker in your browser. When using URL sharing, the state is compressed into the URL hash fragment (#v=1&d=...), which per HTTP specifications is never sent to web servers or logged.

Q:What is the difference between interface and type alias output?

Interfaces in TypeScript support declaration merging and are standard for object contracts. Type aliases allow union and tuple definitions. Both provide identical compile-time type safety in modern TypeScript projects.

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