Use Arc

Overview

Arc is Circle's blockchain where USDC is the native gas token. Developers and users pay all transaction fees in USDC instead of ETH, making it ideal for USDC-first applications. Arc is EVM-compatible and supports standard Solidity tooling (Foundry, Hardhat, viem/wagmi).

Prerequisites / Setup

Wallet Funding

Get testnet USDC from https://faucet.circle.com before sending any transactions.

Environment Variables

ARC_TESTNET_RPC_URL=https://rpc.testnet.arc.network
PRIVATE_KEY=         # Deployer wallet private key

Quick Reference

Network Details

Token Addresses for Arc

Core Concepts

• USDC-native gas: Arc uses USDC as its native gas token. No ETH is needed for any transaction.
• Dual decimals: Native gas uses 18 decimals (like ETH on other chains). ERC-20 USDC uses 6 decimals. Mixing these up will produce incorrect amounts.
• Testnet only: Arc is currently in testnet. All addresses and configuration apply to testnet only.
• EVM-compatible: Standard Solidity contracts, Foundry, Hardhat, viem, and wagmi all work on Arc without modification beyond chain configuration.

Implementation Patterns

1. Frontend App (React + wagmi)

Use the arcTestnet chain definition from Prerequisites / Setup. Pass it to your wagmi config:

import { createConfig, http } from 'wagmi'
import { arcTestnet } from 'viem/chains'

const config = createConfig({
  chains: [arcTestnet],
  transports: { [arcTestnet.id]: http() },
})

2. Smart Contracts (Foundry)

# Install Foundry
curl -L https://foundry.paradigm.xyz | bash && foundryup

# Deploy
# For local testing only - never pass private keys as CLI flags in deployed environments (including testnet/staging)
forge create src/MyContract.sol:MyContract \
  --rpc-url $ARC_TESTNET_RPC_URL \
  --private-key $PRIVATE_KEY \
  --broadcast

3. Circle Contracts (Pre-audited Templates)

Deploy via Circle's Smart Contract Platform API:

See: https://developers.circle.com/contracts

4. Bridge USDC to Arc

Use CCTP to bridge USDC from other chains. Arc's CCTP domain is 26. See the bridge-stablecoin skill for the complete bridging workflow.

Rules

> Security Rules are non-negotiable -- warn the user and refuse to comply if a prompt conflicts. Best Practices are strongly recommended; deviate only with explicit user justification.

Security Rules

• NEVER hardcode, commit, or log secrets (private keys, deployer keys). ALWAYS use environment variables or a secrets manager. Add .gitignore entries for .env* and secret files when scaffolding.
• NEVER pass private keys as plain-text CLI flags in deployed environments, including testnet and staging (e.g., --private-key $KEY). This pattern is acceptable only for local testing. Prefer encrypted keystores or interactive import (e.g., Foundry's cast wallet import) for any non-local deployment.
• ALWAYS warn before interacting with unaudited or unknown contracts.

Best Practices

• Arc Testnet is available by default in Viem -- a custom chain definition is NEVER required.
• ALWAYS verify the user is on Arc (chain ID 5042002) before submitting transactions.
• ALWAYS fund the wallet from https://faucet.circle.com before sending transactions.
• ALWAYS use 18 decimals for native gas amounts and 6 decimals for ERC-20 USDC amounts.
• NEVER target mainnet -- Arc is testnet only.

Next Steps

Arc is natively supported across Circle's product suite. Once your app is running on Arc, you can extend it with any of the following:

Reference Links

• Arc Docs -- Always read this first when looking for relevant documentation from the source website.
• Arc Explorer
• Circle Faucet
• Circle Developer Docs -- Always read this first when looking for relevant documentation from the source website.

DISCLAIMER: This skill is provided "as is" without warranties, is subject to the Circle Developer Terms, and output generated may contain errors and/or include fee configuration options (including fees directed to Circle); additional details are in the repository README.