How to Fix "Unknown file extension .ts" Error When Running Prisma Seed

When running Prisma’s seed command in a Next.js project, you might see this:

TypeError: Unknown file extension ".ts" for prisma/seed.ts at Object.getFileProtocolModuleFormat [as file:] (node:internal/modules/esm/get_format:219:9)
Error: Command failed with exit code 1: ts-node --compiler-options {"module":"CommonJS"} prisma/seed.ts

---

Why It Happens

This happens because:

• Next.js projects usually use ESNext modules in tsconfig.json ("module": "ESNext").
• Prisma’s default seed script expects CommonJS when using ts-node.
• The mismatch causes Node.js to throw the .ts extension error.

---

Quick Reproduction

1. Create a new Next.js project with TypeScript:

npx create-next-app@latest my-app --typescript
cd my-app

2. Add Prisma:

npm install prisma @prisma/client
npx prisma init

3. Create a simple seed file (prisma/seed.ts):

import { PrismaClient } from '@prisma/client';

const prisma = new PrismaClient();

async function main() {
	console.log('Seeding database...');
	// seed logic
}

main()
	.catch((e) => {
		console.error(e);
		process.exit(1);
	})
	.finally(async () => {
		await prisma.$disconnect();
	});

4. Update package.json:

{
	"prisma": {
		"seed": "ts-node --compiler-options {"module":"CommonJS"} prisma/seed.ts"
	}
}

5. Run:

npx prisma db seed

You’ll get the error.

The Simple Fix: Use tsx

tsx is a modern alternative to ts-node that handles ESNext modules out of the box.

1. Install it:

npm install --save-dev tsx

2. Update package.json:

{
	"prisma": {
		"seed": "tsx prisma/seed.ts"
	}
}

3. Run again:

npx prisma db seed

This should work as expected.