JSON to TypeScript
Generate TypeScript interfaces and types from any JSON object automatically.
JSON to TypeScript — Auto-Generating Types for Your API Responses
TypeScript's type system is one of its biggest advantages — catching errors at compile time instead of runtime. But writing TypeScript interfaces for complex API responses manually is tedious and error-prone. When an API returns a response with 20 nested fields, hand-writing the interface takes minutes and introduces typos. Auto-generating types from real JSON takes seconds and is always accurate.
Why type your API responses
Without types, data.user.adress.city (note the typo) only fails at runtime when a user encounters it. With a TypeScript interface, the compiler catches it instantly and shows you the exact line. For applications that fetch data from external APIs, typed responses are the difference between confident refactoring and fear of unknown breakage.
How the generator works
The tool recursively walks your JSON object. Strings become string, numbers become number, booleans become boolean, and null becomes null. Nested objects generate sub-interfaces with names derived from their parent key. Arrays of objects generate a typed array (ItemType[]) with a separate interface for the item type. Arrays of primitives become string[], number[], etc.
Improving generated types
Auto-generated types are a starting point, not a final answer. After generating, review the output: mark fields that might be absent as optional with ?, replace overly broad string types with union types where applicable ("admin" | "user" | "moderator"), and add JSDoc comments for non-obvious fields. The generator saves 90% of the work; you add the domain knowledge.
Frequently asked questions
const data: RootObject = await response.json(). The interface ensures type safety when accessing properties.users array of user objects generates a UsersItem interface and types the field as UsersItem[]. Primitive arrays are typed as string[], number[], etc.null. If you enable "Mark nullable as optional", null fields are typed as fieldName?: Type | null instead. This is useful when the API sometimes omits the field entirely.type RootObject = RootObjectItem[].interface is preferred for objects because it's extensible (supports extends) and produces clearer error messages. type is more flexible for unions and computed types. This tool generates interface by default.