JSON to TypeScript Converter Guide: Generate Types and Interfaces (2026)

The converter analyzes the JSON structure and maps each value to its TypeScript type:

Simple Example

// Input JSON
{ "name": "Raj", "age": 25, "active": true }

// Generated TypeScript
interface Root {
  name: string;
  age: number;
  active: boolean;
}

Real-world JSON is rarely flat. Here is how the converter handles complex structures:

Nested Object

// Input JSON
{
  "user": {
    "name": "Priya",
    "address": {
      "city": "Mumbai",
      "pin": "400001"
    }
  }
}

// Generated TypeScript
interface Address {
  city: string;
  pin: string;
}

interface User {
  name: string;
  address: Address;
}

interface Root {
  user: User;
}

Array of Objects

// Input JSON
{ "users": [{ "id": 1, "name": "Raj" }, { "id": 2, "name": "Priya" }] }

// Generated TypeScript
interface User {
  id: number;
  name: string;
}

interface Root {
  users: User[];
}

The converter creates separate named interfaces for each nested object type, keeping the output clean and reusable.

These are the tricky situations that make manual typing tedious:

Optional Fields

If you provide multiple JSON objects (like an array of records) and a field appears in some but not all, the converter marks it as optional:

// Input: [{ "name": "Raj", "email": "raj@x.com" }, { "name": "Priya" }]
interface Root {
  name: string;
  email?: string;  // optional — missing in second object
}

Nullable Fields

// Input: { "name": "Raj", "phone": null }
interface Root {
  name: string;
  phone: null | string;  // union with null
}

Mixed Arrays

// Input: { "data": [1, "two", true] }
interface Root {
  data: (number | string | boolean)[];
}

The most common use case is generating types from REST API responses. Here is the recommended workflow:

1. Fetch a sample response — Use Postman, curl, or browser DevTools to get a real response from the API endpoint
2. Paste into the converter — Copy the full JSON response and paste it
3. Review and rename — The tool generates names like "Root", "Item", etc. Rename them to meaningful names like "UserResponse", "Product"
4. Add to your project — Copy the generated types into a .ts file (e.g., types/api.ts)
5. Refine manually — Add union literals, enums, or stricter types where you know the exact values

Before and After Refinement

// Generated
interface Product {
  status: string;
  category: string;
}

// Refined
interface Product {
  status: "active" | "draft" | "archived";
  category: "electronics" | "clothing" | "books";
}

The converter lets you choose between interface and type output. Here is when to use each:

Rule of thumb: Use interfaces for API response types and data models. Use type aliases for unions, computed types, and utility types.

Auto-generated types are a starting point, not the final product. Follow these practices:

• Rename generic names — Change "Root" to "ApiResponse", "Item" to "Product", etc. Meaningful names improve code readability.
• Separate request and response types — Do not reuse response types for request payloads. They often differ (POST body has fewer fields than GET response).
• Export from a central file — Keep all API types in a types/ directory. Import from there instead of defining inline.
• Add JSDoc for unclear fields — If the API returns a field like "st" that means "status", add a brief comment.
• Use strict null checks — Enable "strictNullChecks": true in tsconfig.json. This makes null and undefined handling explicit.
• Version your types — When the API changes, update types and fix all type errors rather than using "any" to suppress them.