TypeScript input
parsed
JSON sample output
Paste a TypeScript interface or type alias on the left and a sample JSON conforming to it appears on the right. Field-name aware (id / email / name / url / *At date keys produce realistic values), handles primitives, arrays, nested objects, optionals, unions, literal types, and local refs to other interfaces in the same paste.
The reverse direction of a JSON-to-TypeScript converter: you have a type, you need a sample. Common needs — a fixture for a unit test, a mock body for a Postman/Insomnia collection, a seed for a Storybook story, a placeholder response for a frontend that's ahead of the backend, an example payload to attach to a bug report. Quicktype.io covers this as a side-feature; json2ts.com / transform.tools / the json-to-ts npm CLI do not. The page is a clean wedge for the keyword cluster typescript-to-json / interface-to-mock-data / type-to-sample-json.
What it handles: primitives (string, number, boolean, null), arrays (T[], Array<T>, ReadonlyArray<T>), tuples ([T1, T2]), nested object literals, declared interfaces and type aliases (referenced by name from inside other types), optional properties (key?:), union types (the first non-null member is sampled), intersection types (object members are merged), string- and number-literal types (the literal value is emitted), and Record<K, V> + index signatures (two example keys are emitted). Date is sampled as an ISO 8601 string. any/unknown/never/void sample as null. Field-name heuristics turn id-like / email / name / url / *At keys into realistic values so the output is presentable as a fixture, not just shape-correct.
Out of scope by design: type composition you'd need a real TypeScript compiler for — generic parameter substitution beyond Array/ReadonlyArray/Record/Partial/Readonly/Required, conditional types, mapped types, template-literal types, namespace declarations, declaration merging across files. Paste the resolved shape (the way you'd write it after a hover-preview in your editor) and the output is exact. The conversion is pure client-side JavaScript — your TypeScript stays in your browser tab, nothing is uploaded, no signup. For the forward direction (paste JSON, get a TypeScript interface), use the homepage converter; for the same direction across many JSON shapes, see the long-tail landing pages linked below.