JSON to TypeScript Converter

Turn a sample response into types

1. Paste a JSON document, or press Sample to see an example. The TypeScript appears as you type.
2. Set the root name. The top-level type uses it, and nested objects are named after their keys, so a key called address becomes an Address type.
3. Choose interface or type, and decide whether to add export and readonly.
4. Copy the result or download it as a .ts file.

How the types are worked out

• Strings, numbers and booleans map to string, number and boolean.
• Arrays are merged: the tool reads every item and builds one element type. Objects of the same shape collapse into a single type, and keys that appear in only some items become optional.
• Mixed values produce a union such as string | number. A null is placed last, so you see string | null.
• An empty array has no evidence about its contents, so it becomes unknown[].
• Keys that are not valid identifiers, such as first-name, are quoted.

Tips for better results

• Paste the largest, most varied response you have. More items mean better optional and union detection.
• If a field is sometimes an object and sometimes missing, include one example of each.
• Rename generic names such as Item2 once you have copied the output. The tool adds a number when two different shapes share a name.
• For API contracts that change often, treat the output as a starting point and add runtime validation for data you do not control.
• IDs larger than 2^53 lose precision when parsed as JSON numbers. If your API returns long numeric IDs, change those fields to string by hand.