Quickstart: Set up and transfer USDC on Sei

This quickstart guide helps you write a standalone index.js script that checks your USDC balance and sends a test transfer on the Sei Atlantic-2 Testnet. It’s designed for developers looking to quickly get hands-on with USDC on Sei.

Prerequisites

Before you begin, make sure you have:

• Installed Node.js v18+ and npm, which comes with Node.js.
• Prepared a Sei testnet wallet with USDC and SEI for gas:
  • Set up a Sei-compatible wallet.
  • Request SEI from the faucet.
  • Transfer testnet USDC to Sei using Circle’s CCTP Sample App.
• Stored your private key and a recipient address in a .env file.

USDC contract address

Use the following contract address for USDC on the Sei Atlantic-2 Testnet:

• USDC contract – 0x4fCF1784B31630811181f670Aea7A7bEF803eaED

Part 1: Set up your project

Follow these steps to install dependencies and set up your script environment.

1. Initialize a project

Create a new directory and initialize it with npm:

Shell

mkdir usdc-sei-script
cd usdc-sei-script
npm init -y
npm pkg set type=module

2. Install required dependencies

Install viem and dotenv:

Shell

npm install viem dotenv

3. Create your .env file

In the project root, create a .env file and add the following values:

# Your private key (64 hex characters with 0x prefix)
PRIVATE_KEY=<YOUR_PRIVATE_KEY>

# The address you want to send USDC to
RECIPIENT_ADDRESS=0x<RECIPIENT_ADDRESS>

Your private key must be a 0x-prefixed 64-character hex string.

Part 2: Build your script

Create a file named index.js. You’ll build your script step-by-step in the following sections.

1. Import libraries and define constants

In index.js, start by importing dependencies and setting up the chain and token configuration:

Typescript

// Load environment variables from .env
import "dotenv/config";

// Import Viem utilities for blockchain interaction
import {
  createPublicClient,
  createWalletClient,
  http,
  formatUnits,
  parseUnits,
} from "viem";

// Convert a raw private key string into an account object
import { privateKeyToAccount } from "viem/accounts";

// Define Sei Atlantic-2 testnet chain configuration
const seiTestnet = {
  id: 1328,
  name: "Sei Atlantic-2 Testnet",
  network: "sei-atlantic-2",
  nativeCurrency: { name: "Sei", symbol: "SEI", decimals: 18 },
  rpcUrls: { default: { http: ["https://evm-rpc.atlantic-2.seinetwork.io"] } },
  blockExplorers: {
    default: { url: "https://seitrace.com/?chain=atlantic-2" },
  },
  testnet: true,
};

// Define USDC token address and its decimals on Sei testnet
const USDC_ADDRESS = "0x4fCF1784B31630811181f670Aea7A7bEF803eaED";
const USDC_DECIMALS = 6;

// Define a minimal ABI with only the required functions
const USDC_ABI = [
  {
    name: "balanceOf",
    type: "function",
    stateMutability: "view",
    inputs: [{ name: "account", type: "address" }],
    outputs: [{ name: "", type: "uint256" }],
  },
  {
    name: "transfer",
    type: "function",
    stateMutability: "nonpayable",
    inputs: [
      { name: "to", type: "address" },
      { name: "amount", type: "uint256" },
    ],
    outputs: [{ name: "", type: "bool" }],
  },
];

Learn more: Why use a minimal ABI?

This ABI includes only the two methods needed for this script:

• balanceOf(address) to check the token balance.
• transfer(to, amount) to send USDC.

This makes the ABI compact and easier to understand. Using a minimal ABI:

• Reduces complexity by excluding unrelated functions.
• Speeds up onboarding for new developers.
• Avoids unnecessary contract data that would be unused in this context.

2. Load environment variables and validate inputs

Next, load your credentials from .env and validate them:

Typescript

// Load variables from .env file
const PRIVATE_KEY_RAW = process.env.PRIVATE_KEY;
const RECIPIENT = process.env.RECIPIENT_ADDRESS || process.env.RECIPIENT;

// Validate .env inputs to avoid runtime errors
if (!PRIVATE_KEY_RAW) {
  console.error("Error: Set PRIVATE_KEY in your .env file");
  process.exit(1);
}
if (!RECIPIENT) {
  console.error("Error: Set RECIPIENT_ADDRESS in your .env file");
  process.exit(1);
}
if (!/^0x[a-fA-F0-9]{40}$/.test(RECIPIENT)) {
  console.error("Error: Invalid recipient address");
  process.exit(1);
}

// Ensure the private key has 0x prefix for compatibility
const PRIVATE_KEY = PRIVATE_KEY_RAW.startsWith("0x")
  ? PRIVATE_KEY_RAW
  : "0x" + PRIVATE_KEY_RAW;

Learn more: Input validation and the 'fail fast' principle

Failing fast means catching mistakes early in the execution cycle. This script validates inputs to avoid:

• Missing or undefined environment variables.
• Private keys that are not prefixed with 0x.
• Recipient addresses that don’t follow Ethereum address formatting.

These checks:

• Prevent runtime failures deeper in the logic.
• Help you debug configuration issues immediately.
• Save time and reduce the risk of sending faulty transactions.

3. Set up Viem clients

Set up the Viem clients and your account object:

Typescript

// Convert private key to account object
const account = privateKeyToAccount(PRIVATE_KEY);

// Create a client for reading chain state (for example, balanceOf)
const publicClient = createPublicClient({
  chain: seiTestnet,
  transport: http(),
});

// Create a wallet client for signing and sending transactions
const walletClient = createWalletClient({
  account,
  chain: seiTestnet,
  transport: http(),
});
const walletClient = createWalletClient({
  account,
  chain: seiTestnet,
  transport: http(),
});

Learn more: When to use `publicClient` vs. `walletClient`

• publicClient calls eth_call to read blockchain data. It doesn’t need your private key.
  • Use this for functions like balanceOf, symbol, or decimals.
• walletClient sends transactions using eth_sendTransaction.
  • It signs data with your private key and requires a funded account.

Both clients use the same RPC connection but serve different roles.

4. Check balance and send USDC

Now add the logic to check your balance and send tokens:

Typescript

(async () => {
  try {
    // Read the sender's USDC balance using the balanceOf function
    const balance = await publicClient.readContract({
      address: USDC_ADDRESS,
      abi: USDC_ABI,
      functionName: "balanceOf",
      args: [account.address],
    });

    // Convert raw balance (in smallest units) into readable format (e.g., 250.0 USDC)
    const balanceFormatted = Number(formatUnits(balance, USDC_DECIMALS));

    // Set the amount of USDC to transfer (can be customized)
    const amount = 10;

    // Log the sender address, recipient, and current balance
    console.log("Sender:", account.address);
    console.log("Recipient:", RECIPIENT);
    console.log("USDC balance:", balanceFormatted);

    // Exit if the wallet balance is insufficient
    if (amount > balanceFormatted) {
      console.error("Error: Insufficient USDC balance");
      process.exit(1);
    }

    // Convert the amount to raw format (10 USDC = 10 * 10^6 units)
    const amountInDecimals = parseUnits(amount.toString(), USDC_DECIMALS);

    // Send the USDC by calling the transfer function of the token contract
    const hash = await walletClient.writeContract({
      address: USDC_ADDRESS,
      abi: USDC_ABI,
      functionName: "transfer",
      args: [RECIPIENT, amountInDecimals],
    });

    // Log the transaction hash and a link to view it on the Sei block explorer
    console.log("Transfer successful!");
    console.log("Tx hash:", hash);
    console.log(
      "Explorer:",
      `https://seitrace.com/?chain=atlantic-2&tx=${hash}`,
    );
  } catch (err) {
    // Log any errors that occur (e.g., RPC errors, contract reverts)
    console.error("Transfer failed:", err.message || err);
    process.exit(1);
  }
  // Exit cleanly after the transfer completes
  process.exit(0);
})();

Learn more: Handling USDC units with `formatUnits` and `parseUnits`

Token contracts use the smallest indivisible unit of a token. For USDC, that’s 6 decimal places.

• formatUnits(value, 6) converts raw blockchain balances into readable amounts like 250.0.
• parseUnits('10', 6) converts user inputs into raw values like 10000000 (10 * 10^6).

These utilities:

• Prevent incorrect math during transfer.
• Ensure compatibility with ERC-20 functions.
• Improve display formatting in logs and UI.

Part 3: Run your script

To run your script, use the following command:

Shell

node index.js

Sample output

If the script runs successfully, your terminal will print a transaction summary like this:

Sender: 0x1A2b...7890
Recipient: 0x9F8f...1234
USDC balance: 250.0
Transfer successful!
Tx hash: 0xabc123...def456
Explorer: https://seitrace.com/?chain=atlantic-2&tx=0xabc123...def456

You can open the explorer link in your browser to view the transaction on SeiTrace.

Additional notes

• Testnet only: This guide runs on the Sei testnet. Tokens and transfers here are not real and hold no value.
• Security best practices: Always store sensitive data like private keys in environment variables. Never hardcode or commit .env files to version control.
• Gas fees: All EVM-compatible chains require gas. Be sure to request testnet SEI from the faucet so your transactions can be mined.
• Lightweight ABI: The ABI used here is minimal. It includes only the functions necessary for balance checks and transfers, which keeps the script lean.
• Auto-prefixing: Some tools or environments strip the 0x prefix from private keys. This script adds it back if needed to avoid errors.