Convert a Simple JSON Object to a TypeScript Interface

From JSON to a TypeScript Interface

The most common conversion is turning a simple, flat JSON object into a TypeScript interface. Each key in the JSON object becomes a property, and the value determines the type.

Example JSON

{
  "id": 42,
  "name": "Alice",
  "email": "alice@example.com",
  "isActive": true,
  "score": 98.5
}

Generated TypeScript

interface User {
  id: number;
  name: string;
  email: string;
  isActive: boolean;
  score: number;
}

How the Mapping Works

TypeScript has a direct correspondence for every JSON primitive:

JSON type	TypeScript type
string	string
number	number
boolean	boolean
null	null

Integers and floating-point numbers both map to number because JSON does not distinguish between them, and neither does TypeScript at the type level. If you need to enforce integer-only values, you can add runtime validation or use branded types.

Best Practices

• Use PascalCase for interface names (e.g., User, ProductDetail).
• Prefer interface over type alias for object shapes when you do not need unions or intersections, since interfaces support declaration merging and can be extended.
• Keep property names in camelCase to match JavaScript conventions. If your JSON uses snake_case, the converter preserves the original keys but you may want to transform them in a mapping layer.

A simple flat object is the foundation. Once you are comfortable with this, nested objects, arrays, and optional properties are natural next steps.