JSON to TypeScript: Stop Hand-Writing Interface Definitions

Why generate types?

Catch typos and null access at compile time; use real payloads when OpenAPI is missing or stale.

Manual mapping example

{ "id": 1, "name": "Alice", "email": null }

interface User {
  id: number;
  name: string;
  email: string | null;
}

Nested arrays and unions

Empty arrays need a manual element type; heterogeneous arrays become unions.

Optional vs null

Missing keys (email?) differ from null values (email: string | null)—align with backend semantics.

Tools

quicktype CLI, json-schema-to-typescript, online json2ts for one-offs.

# npx quicktype sample.json -o types.ts --lang typescript

Best practices

Regenerate instead of editing generated files; use multiple samples; let tsc surface breaking API changes.