npm install @cowprotocol/contracts

import {
  domain,
  Order,
  OrderKind,
  signOrder,
  SigningScheme,
} from "@cowprotocol/contracts";
import { ethers } from "ethers";

// Configure domain
const settlementDomain = domain(
  1, // Ethereum mainnet
  "0x9008D19f58AAbD9eD0D60971565AA8510560ab41"
);

// Create order
const order: Order = {
  sellToken: "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
  buyToken: "0x6B175474E89094C44Da98b954EedeAC495271d0F",
  sellAmount: ethers.utils.parseEther("1.0"),
  buyAmount: ethers.utils.parseEther("2000"),
  validTo: Math.floor(Date.now() / 1000) + 3600,
  appData: ethers.constants.HashZero,
  feeAmount: ethers.utils.parseEther("0.01"),
  kind: OrderKind.SELL,
  partiallyFillable: false,
  receiver: ethers.constants.AddressZero,
};

// Sign order
const wallet = new ethers.Wallet("YOUR_PRIVATE_KEY");
const signature = await signOrder(
  settlementDomain,
  order,
  wallet,
  SigningScheme.EIP712
);