JSON to TypeScript Interface Generator Online
Auto-generate TypeScript interfaces from any JSON โ nested objects ยท optional fields ยท readonly ยท export ยท 100% Free
export interface User {
id: number;
name: string;
active: boolean;
address: Address;
}TypeScript interfaces define the shape of your data โ and generating them from real JSON ensures they match your actual API responses. This online interface generator handles nested objects (generates sub-interfaces), arrays of objects (generates typed arrays), optional fields (? modifier) and all JSON primitive types. Copy the output directly into your TypeScript project.
What is JSON to TypeScript Interface Generation?
This tool analyses the structure of your JSON data and automatically generates TypeScript interface or type declarations โ saving you the time of writing them manually. It infers string, number, boolean, null, nested object interfaces, and typed arrays. When your JSON is an array of objects, optional fields are detected automatically.
How Nested Objects Are Handled
Every nested JSON object generates its own named TypeScript interface. For example, if your JSON has "address": { "city": "Ahmedabad" }, the tool generates a separate Address interface and references it as address: Address in the parent interface โ matching real-world TypeScript project structure.
Frequently Asked Questions
How are nested JSON objects converted to TypeScript interfaces?
Each nested object becomes a separate interface. Naming convention: parent key name capitalized. Example: {"user": {"address": {}}} generates interface Address{}, interface User{ address: Address; }, interface Root{ user: User; }. This keeps each interface small and focused, following TypeScript best practices.
Can I generate TypeScript interfaces for JSON arrays at the root level?
Yes โ if your JSON root is an array (e.g., [{...}, {...}]), the generator detects the array item type and generates interface Item {} with export type Root = Item[]. This is common for API endpoints that return lists of resources.
How do I make TypeScript interface fields optional vs required?
Required: field: type (no ?). Optional: field?: type. When generating from JSON: all fields detected are marked required by default (they exist in your sample). Mark as optional (?): fields that may be absent in some responses, fields that are null in some cases, fields added in future API versions.
Should I use readonly in TypeScript interfaces for API response types?
For API response types that shouldn't be mutated: add readonly to all fields. Best practice: interface ApiUser { readonly id: number; readonly name: string; }. The generator can output readonly interfaces โ use them for API responses (data from server shouldn't be mutated). For form data or mutable state, skip readonly.