How to Auto-Generate TypeScript Types & Zod Schemas from JSON

Modern frontend and backend engineering in Next.js, Node.js, and React requires strict type safety. When integrating third-party APIs (Stripe, GitHub, internal microservices), manually writing TypeScript interfaces for 50-field JSON payloads is tedious and error-prone.

Furthermore, static types provide zero runtime protection. If an API returns null instead of a string, your application will throw an uncaught runtime error.

This guide demonstrates how to generate static TypeScript types and runtime Zod validation schemas directly from JSON.

1. TypeScript Interface Generation

Given a raw API response:

{
  "orderId": "ord_98765",
  "totalAmount": 149.99,
  "isPaid": true,
  "customer": {
    "name": "Sarah Connor",
    "email": "sarah@cyberdyne.com"
  },
  "tags": ["express", "priority"]
}

The generated TypeScript interfaces:

export interface Customer {
  name: string;
  email: string;
}

export interface OrderResponse {
  orderId: string;
  totalAmount: number;
  isPaid: boolean;
  customer: Customer;
  tags: string[];
}

2. Converting to Runtime Zod Schemas

To validate this payload dynamically at runtime (for example in Next.js Server Actions or Route Handlers):

import { z } from "zod";

export const CustomerSchema = z.object({
  name: z.string().min(1),
  email: z.string().email(),
});

export const OrderResponseSchema = z.object({
  orderId: z.string().startsWith("ord_"),
  totalAmount: z.number().positive(),
  isPaid: z.boolean(),
  customer: CustomerSchema,
  tags: z.array(z.string()),
});

// Automatically infer static TypeScript type from runtime schema
export type OrderResponse = z.infer<typeof OrderResponseSchema>;

3. Safe Parsing in Next.js API Routes

export async function POST(request: Request) {
  const json = await request.json();
  
  const parseResult = OrderResponseSchema.safeParse(json);
  
  if (!parseResult.success) {
    return Response.json(
      { error: "Validation Failed", details: parseResult.error.flatten() },
      { status: 422 }
    );
  }
  
  // parseResult.data is 100% type-safe and validated
  const order = parseResult.data;
  return Response.json({ success: true, orderId: order.orderId });
}