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.