douni.one / Converter comparison

A transform.tools alternative for JSON to TypeScript

Use this comparison if you want explicit null types, mixed-field unions, a custom root name, or Japanese walkthroughs. douni.one and transform.tools are independent sites.

Try JSON to TypeScript

One input, two outputs

Checked on the public transform.tools page on September 26, 2026, with Create Mono Type off. Whitespace and semicolons are normalized below. Its behavior may change after updates.

[{"id":1,"name":"Tokyo"},{"id":"002","name":null}]

douni.one

export type Root = RootValueItem[];

export interface RootValueItem {
  id: number | string;
  name: string | null;
}

transform.tools

export type Root = Root2[];

export interface Root2 {
  id: any;
  name?: string;
}

In this sample, id takes both numbers and strings, and name exists in every item. douni.one emits number | string for id and string | null for name, keeping a null value distinct from an absent field.

This sample is not an overall accuracy benchmark. Both tools infer from supplied data; neither knows your complete API contract or validates values at runtime. Try your own samples and check the output with your project's TypeScript settings.

Options and workflow

Options and workflow
Feature	douni.one	transform.tools
JSON to TypeScript style	Interfaces or an inline type alias	Interfaces or Create Mono Type
Root type name	Editable input, for example ApiResponse	Root in the inspected UI; editable in the copied output
Null and mixed-field sample	Output above, plus three loadable examples	See the observed output above
Japanese walkthroughs	Examples, limitations and FAQs for the four tools below	Inspected JSON to TypeScript UI was in English

Choose for the task in front of you

Transform.tools is an open-source converter with many JSON, GraphQL and SVG targets. Its directory is useful when you already know which transformation you need. Try douni.one when you want Japanese guidance, loadable examples, or explicit control over a JSON-generated type's name and null handling.

Try a working example

Input handling and limits

On douni.one, JSON to TypeScript and TOML to JSON convert in your browser. HTML to Pug and TypeScript to JavaScript send input to the server. Input can persist within the same tab; clear it on shared devices. This is a statement about conversion, not a claim that the site has no advertising or analytics requests.