Typing an API response
Paste a real response body and get the interface. Then widen any fields the API documents as optional or nullable.
JSON to TypeScript
Generate TypeScript interfaces from a JSON sample in your browser.
Maintained by Roshan.
Use JSON to TypeScript
Converts json sample to typescript in this tab, with nothing sent anywhere.
Runs entirely on your deviceThe conversion happens in this browser tab. Nothing you type is uploaded, logged or stored, which is worth knowing for anything you would not paste into a search box.
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Browse all generatorsAbout JSON to TypeScript
Writing a TypeScript interface by hand from a real API response is tedious and easy to get subtly wrong - a mistyped field, a missed nesting, a number where a string should be. Generating it from an actual sample removes the guesswork: paste the JSON your API really returns, and get the interface that matches it. This infers the shape recursively, so a nested object becomes its own named interface rather than an inline blob, which is how you would write it by hand and what keeps the types readable. The inference is deliberately conservative - it describes exactly what the sample contains and does not invent optional fields or unions a single example cannot prove - so the output is an accurate starting point you refine, not a guess dressed up as certainty.
Using JSON to TypeScript
- The JSON is parsed and its structure inferred recursively, field by field.
- Each nested object becomes its own named interface, referenced by the parent, so the types read the way you would write them.
- Arrays are typed by their first element, and the element type of an object array gets a sensible singular name.
- Primitive types map directly: a JSON string becomes string, a number becomes number, a boolean becomes boolean.
- You can name the root interface; nested ones are named from their field keys.
Where json to typescript helps
Bootstrapping a data model
Generate the interfaces from sample data, then refine names and optionality by hand.
Before you use the result
- A single sample cannot prove a field is optional or that an array is heterogeneous, so it types what it sees rather than guessing wider unions. Widen the result yourself where the API allows nulls or variation.
- An empty array is typed as unknown[], since there is no element to infer from.
- A null value is typed as null; if the field is really 'string or null', adjust it after.
- All numbers become number; TypeScript has no integer type to distinguish them.
- The output is a faithful starting point to refine, not an exhaustive contract.
Questions about JSON to TypeScript
Does it handle nested objects?
Yes. Each becomes its own named interface referenced by its parent, rather than an inline type.
Why aren't any fields optional?
A single sample cannot prove optionality. It types what the example contains; widen fields to optional or nullable yourself.
How are arrays typed?
By their first element. An empty array becomes unknown[], since there is nothing to infer.
Can I name the root type?
Yes. There is a field for the root name; nested interfaces are named from their keys.
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