use-arc

Original：🇺🇸 English

Translated

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.

2installs

Sourcecirclefin/skills

Added on2026-04-15

NPX Install

npx skill4agent add circlefin/skills use-arc

SKILL.md Content

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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

bash

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

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:

typescript

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

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

2. Smart Contracts (Foundry)

bash

# 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

. 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:

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.