What does it do?
It reads a JSON sample — an API response, a fixture, a config file — and writes the TypeScript interfaces that describe it. Nested objects become their own named interfaces, so you get readable, reusable types instead of one giant inline type.
The inference runs with quicktype inside a Web Worker, so even large samples never freeze the page, and nothing leaves your browser.
How to use it
- Paste a JSON object or, better, an array with several examples of the same entity.
- Name the root type (
User, Order…). Nested types are named after their keys.
- Choose
interface or type, and enable readonly if your data is immutable.
- Copy the result into your project.
Example
[{ "id": 1, "email": "ada@example.com" }, { "id": 2 }]
becomes
export interface User {
id: number;
email?: string;
}
Tips
- Types are only as good as the sample: include an example of every variant your API can return.
- For runtime validation, generate a schema with the JSON to Zod tool instead.
Frequently asked questions
›How does it decide which fields are optional?
When you paste an array of objects, a field that is missing in at least one object becomes optional (field?: type). Paste several real examples to get more accurate types.
›What happens with null values and mixed arrays?
A field that is always null is typed as null, one that is sometimes null becomes a union with null, and an array that mixes numbers and strings becomes Array<number | string>.
›Interface or type: which one should I use?
Both describe the shape of an object. Interfaces can be extended and merged, which suits public APIs; type aliases can also express unions and mapped types. Pick whatever your codebase already uses.