Paste any JSON — get perfect TypeScript interfaces. Handles nested objects, arrays, nullables, union types, and more.
TypeScript interfaces provide compile-time type checking for your JavaScript code. When you're working with API responses, config files, or any JSON data, having proper TypeScript interfaces catches bugs before they reach production.
string | null union types[{...}, {...}] API responses?Both interface and type work for object shapes in TypeScript. Interfaces support declaration merging and extending, making them better for public APIs. Type aliases support unions and intersections, making them more flexible for complex types.
// Interface (recommended for objects)
interface User {
name: string;
age: number;
}
// Type alias (works too)
type User = {
name: string;
age: number;
}
Copy a sample response from your browser's DevTools Network tab, paste it here, and get instant TypeScript interfaces. Use these in your fetch calls:
const response = await fetch('/api/users');
const data: User[] = await response.json();
readonly for data you don't modify (API responses, configs)Like this tool? Check out our other free dev tools
Browse 45+ Free Tools →JSON to TypeScript conversion generates TypeScript interface definitions from a JSON object. The tool analyzes your JSON structure, infers the type of each property (string, number, boolean, array, nested object), and outputs typed interfaces you can use directly in TypeScript projects to enforce type safety without writing boilerplate manually.
Both work, but interfaces are preferred for JSON-derived types representing objects. Interfaces support declaration merging, are more readable in error messages, and signal intent as a data contract. Use type aliases when you need union types, mapped types, or conditional types. For simple JSON shapes, interface is the idiomatic TypeScript choice.
Nested objects are extracted into separate named interfaces. For example, a user object with an address field becomes two interfaces: User and Address, with User containing address: Address. This keeps types modular and reusable. Arrays of objects generate typed arrays like items: Item[] with a separate Item interface for the element shape.
When a JSON value is null, the generator typically produces a union type like string | null or uses optional property syntax (property?: type). Null handling depends on the tool settings. In strict TypeScript with strictNullChecks enabled, null values must be explicitly typed, so the generator marks them as nullable to prevent runtime errors.
Yes. Copy any JSON response from your browser's network tab, Postman, or a fetch call and paste it directly. The converter accepts any valid JSON including deeply nested structures, arrays of objects, and mixed types. This is the fastest way to generate TypeScript interfaces for third-party API responses.