Strict Type Inference · Client-Side · Zero Telemetry

JSON to TypeScript Converter

Paste any JSON data or API response to instantly create type-safe TypeScript interfaces and type definitions with nested object recursion.

Root Type Name:

exportOptional ( ? )

Indent:

Input JSON

Presets:

TypeScript Output

export interface UserProfile {
  id: number;
  username: string;
  email: string;
  isActive: boolean;
  role: string;
  avatarUrl: null;
  tags: string[];
  profile: Profile;
  stats: Stats;
}

export interface Coordinates {
  lat: number;
  lng: number;
}

export interface Location {
  city: string;
  country: string;
  coordinates: Coordinates;
}

export interface Profile {
  firstName: string;
  lastName: string;
  bio: string;
  location: Location;
}

export interface ContributionsItem {
  year: number;
  count: number;
}

export interface ContributionsItem2 {
  year: number;
  count: number;
}

export interface Stats {
  followers: number;
  following: number;
  contributions: (ContributionsItem | ContributionsItem2)[];
}

Automatically parses nested objects, resolves mixed & homogenous arrays, and preserves property name validity.

TypeScript Type Generation Best Practices

Interfaces vs. Type Aliases in Modern TypeScript

Both interface and type declare object contracts in TypeScript, but they differ in extensibility:

Interface: Supports declaration merging and extension via extends. Ideal for public library APIs and domain entity modeling.
Type Alias: Supports union types (A | B), intersection types, mapped types, and tuple types that interfaces cannot represent.

Handling Dynamic and Nullable API Payloads

REST and GraphQL payloads frequently return null for unset fields or omit keys entirely depending on user permissions:

Enable the Optional Fields (?) toggle when typing endpoints that do not guarantee presence of all fields.
Combine the generated TypeScript models with validation libraries like Zod or Yup to enforce runtime contract guarantees.