Question 1

How does the interface generator work?

Accepted Answer

Paste a JSON sample (a single object, an array, or an array of multiple samples) and the engine recursively infers the type of each value, extracts nested objects into their own interfaces, and emits clean TypeScript declarations. Strings, numbers, booleans, null, arrays, and nested objects are all handled. Optional fields are detected when you provide multiple samples and a key is missing in some of them.

Question 2

How are optional, nullable, and union types handled?

Accepted Answer

Nullable fields (where 'null' appears alongside another type) become optional with the '?' modifier (or '| undefined' if you prefer). When a field has different types across samples — say string in one and number in another — the engine emits a union type like 'string | number'. Mixed-type arrays also produce union element types, with a warning suggesting you add more samples for accurate optionals.

Question 3

Can I generate runtime validators and enums?

Accepted Answer

Yes. Toggle 'validators' to emit a TypeScript type-guard function (is) for each interface — these check the shape at runtime and narrow the type via 'v is '. Toggle 'enum inference' to detect small string-or-number literal sets in arrays and emit string-literal unions (e.g. "open" | "closed" | "pending") instead of plain string types.

Question 4

What extra features does this tool have compared to others?

Accepted Answer

(1) Recursive nested-object extraction into separate interfaces. (2) Multi-sample merging for accurate optional-field detection. (3) Optional + nullable handling with two styles (? vs | undefined). (4) Union types for mixed-type fields. (5) String-literal and number-literal enum inference. (6) Runtime type-guard (validator) generation. (7) JSDoc comments from key names. (8) Interface vs type toggle. (9) Readonly toggle. (10) Export toggle. (11) Bracket vs generic array style (T[] vs Array<T>). (12) Empty-array handling with 'unknown[]' + warning. (13) Mixed top-level warning. (14) Root-name + key-path-based interface naming with singularization. (15) Reserved-word and invalid-identifier handling (quotes and suffixes). (16) Copy + Download .ts. (17) History (localStorage, last 20). (18) Shareable URL. (19) Sample presets. (20) Optional BYO-key LLM enhancement.

Question 5

Is my JSON sent anywhere?

Accepted Answer

No. All JSON parsing, type inference, and TypeScript generation runs locally in your browser. Your data never leaves this device. The only network call is if you paste your own LLM API key and click 'Enhance' — that request goes directly from your browser to the LLM provider you choose. Types reflect only the sample(s) you paste; add multiple responses for accurate optionals. Nothing uploaded or logged by us.

AI TypeScript Interface Generator

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