JSON → TypeScript

The fastest way to add types to an API integration is to copy the JSON response directly from Postman (or Insomnia, or your browser's DevTools Network tab), paste it into this tool, and copy the generated TypeScript interface back into your codebase. The entire process takes under ten seconds and produces types that accurately reflect the actual API shape — no guesswork, no manual field-by-field typing.

Step-by-step workflow

In Postman, send your API request and click the response body. Select all (Ctrl+A / Cmd+A) and copy. Paste into the JSON input above. The tool immediately generates a TypeScript interface. Adjust the root interface name (e.g., UserResponse), toggle options like optional fields and export, then copy the output and drop it into your types/ folder.

// Postman response → paste → instant types
{ "user": { "id": 42, "role": "admin", "verified": null } }

// Generated TypeScript
export interface UserResponse {
  user: User;
}
export interface User {
  id: number;
  role: string;
  verified?: string | number | boolean | null;
}

Why this beats writing types by hand

A deeply nested API response with five levels of objects, arrays of discriminated unions, and nullable fields can take a developer 20–30 minutes to type correctly by hand — and that's before verifying the output against real data. This tool does it in milliseconds. For large APIs with dozens of endpoints, the time savings compound into hours per sprint.

Using the Zod output

Switch to "Zod" mode to get a z.object() schema alongside your interface. This is useful for validating API responses at runtime — particularly important when you don't fully control the backend and the actual response shape might drift from documentation. The Zod schema and the TypeScript interface stay in sync because both derive from the same JSON input.

Every any in a TypeScript codebase is a broken promise to the compiler — and to every developer who reads the code after you. Using any disables type checking for that variable entirely, meaning TypeScript provides zero protection when the shape of a value changes or is misused. A generated interface costs ten seconds to produce and saves potentially hours of debugging.

What type safety actually prevents

• Refactoring safety — rename a field in your interface and every broken usage becomes a compiler error, not a production crash.
• Self-documenting code — interfaces are the most accurate documentation that exists, because they're enforced and always current.
• IDE superpowers — precise autocompletion, inline docs, and instant error highlighting all depend on accurate types.
• API contract enforcement — when the backend changes a response shape, TypeScript surfaces every affected line immediately.
• Onboarding speed — a new developer can understand an unfamiliar API by reading its interface in under a minute.

Null safety in practice

Real API responses frequently include null fields — a value that exists in the schema but hasn't been set yet. This tool detects null values and generates string | number | boolean | null union types, and optionally marks the field with ? to indicate it might be absent entirely. This prevents the most common runtime error in JavaScript: accessing a property on null.