Is my JSON sent to a server?

No. Parsing and type inference happen entirely in your browser with the built-in JSON object. Nothing is transmitted.

How are array element types inferred?

If every element is an object, all elements are merged into a single interface (keys present in some but not others become optional). Otherwise the distinct element types are unioned — e.g. [1, "hi"] becomes (number | string)[].

Why are nested interfaces named after the parent key?

So you get readable names like `User` and `UserAddress` instead of `Root1`, `Root2`. Array keys are singularised (users → User).

What about JSON with circular references?

JSON itself cannot represent cycles, so this is never an issue. The generator works on the parsed JSON value tree.

Developer Tools

JSON to TypeScript

Paste any JSON payload and instantly get clean TypeScript interfaces. Handles nested objects, arrays of mixed shapes, optional fields and union element types — all generated in your browser, nothing uploaded.

Your input is processed locally in your browser. It is not uploaded to Dueneo.

Loading JSON to TypeScript…

How to use

1
Paste your JSON
Drop any valid JSON — an API response, a config file, a fixture — into the left-hand editor.
2
Pick a root name and style
Name the top-level interface (default `Root`) and choose between `interface` and `type` declarations.
3
Toggle optional fields
When an array contains objects with differing keys, the missing keys become optional (`?`) fields. Turn this off to force every field required.
4
Generate and copy
Click Generate. Nested objects get their own interfaces named after the parent key (singularised for arrays). Copy the result straight into your `.ts` file.

Common use cases

Generate TypeScript types for an API you don't control and don't have an OpenAPI spec for.
Turn a JSON config fixture into strict types so future edits are caught at compile time.
Quickly sketch the shape of a third-party webhook payload before writing the handler.
Bootstrap a typed client for an internal service from a sample response.

Limitations

Inputs larger than 1 MB are rejected to keep the tab responsive.
The union-of-primitives inference is structural — `42` and `\"hello\"` in the same array become number | string, not a string-literal union.
Empty arrays become unknown[] because the element type cannot be inferred.
String enums and string-literal unions are not detected — every string becomes string.
JSON keys that aren't valid identifiers are emitted as quoted property names.

Frequently asked questions

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Loading JSON to TypeScript…

How to use

Paste your JSON

Drop any valid JSON — an API response, a config file, a fixture — into the left-hand editor.

Pick a root name and style

Name the top-level interface (default `Root`) and choose between `interface` and `type` declarations.

Toggle optional fields

When an array contains objects with differing keys, the missing keys become optional (`?`) fields. Turn this off to force every field required.

Generate and copy

Click Generate. Nested objects get their own interfaces named after the parent key (singularised for arrays). Copy the result straight into your `.ts` file.

Common use cases

Generate TypeScript types for an API you don't control and don't have an OpenAPI spec for.

Turn a JSON config fixture into strict types so future edits are caught at compile time.

Quickly sketch the shape of a third-party webhook payload before writing the handler.

Bootstrap a typed client for an internal service from a sample response.

Limitations

Inputs larger than 1 MB are rejected to keep the tab responsive.
The union-of-primitives inference is structural — `42` and `\"hello\"` in the same array become number | string, not a string-literal union.
Empty arrays become unknown[] because the element type cannot be inferred.
String enums and string-literal unions are not detected — every string becomes string.
JSON keys that aren't valid identifiers are emitted as quoted property names.