use-arc

name use-arc description Provide instructions on how to build with Arc, Circle's blockchain where USDC is the native gas token. Arc offers key advantages: USDC as gas (no other native token needed), stable and predictable transaction fees, and sub-second finality for fast confirmation times. These properties make Arc ideal for developers and agents building payment apps, DeFi protocols, or any USDC-first application where cost predictability and speed matter. Use skill when Arc or Arc Testnet is mentioned, working with any smart contracts related to Arc, configuring Arc in blockchain projects, bridging USDC to Arc via CCTP, or building USDC-first applications. Triggers: Arc, Arc Testnet, USDC gas, deploy to Arc, Arc chain, stable fees, fast finality. 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 Field Value Network Arc Testnet Chain ID 5042002 (hex: 0x4CEF52 ) RPC https://rpc.testnet.arc.network WebSocket wss://rpc.testnet.arc.network Explorer https://testnet.arcscan.app Faucet https://faucet.circle.com CCTP Domain 26 Token Addresses for Arc Token Address Decimals USDC 0x3600000000000000000000000000000000000000 6 (ERC-20) EURC 0x89B50855Aa3bE2F677cD6303Cec089B5F319D72a 6 Core Concepts Native gas IS USDC — one balance, two interfaces (not two assets) : On Arc the native gas asset is USDC itself. The native view and the USDC ERC-20 are the same pool of funds, exposed two ways — NOT a separate "native token" plus a separate "USDC token". Drop the ETH-style mental model from other chains. Native view : 18 decimals. Used only for gas and msg.value . wagmi useBalance returns this (its symbol is USDC ). ERC-20 view : 6 decimals, at 0x3600000000000000000000000000000000000000 . Use this for all balances, transfers, approvals, and display. Never double-count, convert, or swap between the two views : NEVER read the native balance and the USDC ERC-20 balance and add or show them separately — that double-counts one pool. Show a single USDC balance (the 6-decimal ERC-20 view). USDC ↔ native is NOT a swap or conversion — it is the same asset. Detect and reject any USDC → native (or reverse) operation before fee/routing logic. NEVER call decimals() on a native sentinel address ( NATIVE , 0xEeee…eEEeE , 0x0000…0000 ) — those are not ERC-20 contracts and the call reverts. The ERC-20 is 6 decimals; native is 18. The two views differ by a factor of 10^12 ( 1e18 native = 1e6 ERC-20). Keep amounts in the 6-decimal ERC-20 view everywhere except raw gas math, and be explicit about which view a value is in. 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: Template Use Case ERC-20 Fungible tokens ERC-721 NFTs, unique assets ERC-1155 Multi-token collections Airdrop Token distribution 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 keep USDC amounts in the 6-decimal ERC-20 view for balances, transfers, and display; use 18-decimal native units ONLY for raw gas / msg.value math. Never sum the two views or treat native and USDC as separate assets. 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: Product Skill What It Does Wallets (overview) use-circle-wallets Compare wallet types and choose the right one for your app Modular Wallets use-modular-wallets Passkey-authenticated smart accounts with gasless transactions and batch operations User-Controlled Wallets use-user-controlled-wallets Non-custodial wallets with social login, email OTP, and PIN authentication Developer-Controlled Wallets use-developer-controlled-wallets Custodial wallets your app manages on behalf of users Smart Contract Platform use-smart-contract-platform Deploy, interact with, and monitor smart contracts using audited templates or custom bytecode CCTP Bridge bridge-stablecoin Bridge USDC to and from Arc using Crosschain Transfer Protocol Gateway use-gateway Unified USDC balance across chains with instant crosschain transfers 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 .