Agent skill

Use Arc

Provide instructions on how to build with Arc, Circle's blockchain where USDC is the native gas token.

Apache-2.0Auto-check: notesBackend & APIs

Install Use Arc

skills CLI

$ npx skills add circlefin/skills --skill use-arc -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI

$ gh skill install circlefin/skills use-arc --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy

$ git clone --depth 1 https://github.com/circlefin/skills.git skills-src && mkdir -p .claude/skills && cp -r skills-src/plugins/circle/skills/use-arc .claude/skills/use-arc && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Paste into Claude Code

Install the "use-arc" agent skill from https://github.com/circlefin/skills/tree/master/plugins/circle/skills/use-arc into .claude/skills/use-arc/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "use-arc", then confirm the skill loads.

Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

$skill-installer

$skill-installer install https://github.com/circlefin/skills/tree/master/plugins/circle/skills/use-arc

Type this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.

skills CLI

$ npx skills add circlefin/skills --skill use-arc -a codex

Project install goes to .agents/skills/; add -g for ~/.codex/skills/.

GitHub CLI

$ gh skill install circlefin/skills use-arc --agent codex

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/circlefin/skills.git skills-src && mkdir -p .agents/skills && cp -r skills-src/plugins/circle/skills/use-arc .agents/skills/use-arc && rm -rf skills-src

Use ~/.agents/skills/ instead of .agents/skills for a personal install.

Codex skills documentation · loads skills from .agents/skills/

Paste into Codex

Install the "use-arc" agent skill from https://github.com/circlefin/skills/tree/master/plugins/circle/skills/use-arc into .agents/skills/use-arc/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "use-arc", then confirm the skill loads.

Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add circlefin/skills --skill use-arc -a cursor

Project install goes to .agents/skills/; add -g for ~/.cursor/skills/.

GitHub CLI

$ gh skill install circlefin/skills use-arc --agent cursor

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/circlefin/skills.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/plugins/circle/skills/use-arc .cursor/skills/use-arc && rm -rf skills-src

Use ~/.cursor/skills/ instead of .cursor/skills for a personal install.

Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/

Paste into Cursor

Install the "use-arc" agent skill from https://github.com/circlefin/skills/tree/master/plugins/circle/skills/use-arc into .cursor/skills/use-arc/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "use-arc", then confirm the skill loads.

Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

gemini skills install

$ gemini skills install https://github.com/circlefin/skills.git --path plugins/circle/skills/use-arc

--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.

skills CLI

$ npx skills add circlefin/skills --skill use-arc -a gemini-cli

Project install goes to .agents/skills/; add -g for ~/.gemini/skills/.

GitHub CLI

$ gh skill install circlefin/skills use-arc --agent gemini-cli

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/circlefin/skills.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/plugins/circle/skills/use-arc .gemini/skills/use-arc && rm -rf skills-src

Use ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.

Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/

Paste into Gemini CLI

Install the "use-arc" agent skill from https://github.com/circlefin/skills/tree/master/plugins/circle/skills/use-arc into .gemini/skills/use-arc/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "use-arc", then confirm the skill loads.

Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

GitHub CLI

$ gh skill install circlefin/skills use-arc

Installs for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).

skills CLI

$ npx skills add circlefin/skills --skill use-arc -a github-copilot

Project install goes to .agents/skills/; add -g for ~/.copilot/skills/.

Manual copy

$ git clone --depth 1 https://github.com/circlefin/skills.git skills-src && mkdir -p .github/skills && cp -r skills-src/plugins/circle/skills/use-arc .github/skills/use-arc && rm -rf skills-src

Use ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.

GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/

Paste into GitHub Copilot

Install the "use-arc" agent skill from https://github.com/circlefin/skills/tree/master/plugins/circle/skills/use-arc into .github/skills/use-arc/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "use-arc", then confirm the skill loads.

GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add circlefin/skills --skill use-arc -a opencode

OpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.

GitHub CLI

$ gh skill install circlefin/skills use-arc --agent opencode

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/circlefin/skills.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/plugins/circle/skills/use-arc .opencode/skills/use-arc && rm -rf skills-src

Use ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.

OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/

Paste into OpenCode

Install the "use-arc" agent skill from https://github.com/circlefin/skills/tree/master/plugins/circle/skills/use-arc into .opencode/skills/use-arc/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "use-arc", then confirm the skill loads.

OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

Facts

Skill name: use-arc
GitHub stars: 155
Token cost: ~2.1k tokens
SKILL.md length: 902 words
Files: 2 (incl. references)
Skills in repo: 18
Repo updated: Sep 16, 2026
First seen: Oct 7, 2026
Licence: Apache-2.0

At a glance

Provide instructions on how to build with Arc, Circle's blockchain where USDC is the native gas token.

Works in 3 steps: Configure the chain — use the built-in… → Deploy contracts — standard… → Bridge USDC in — Arc's CCTP domain is…
Tasks that involve Smart contracts
SKILL.md covers Overview, Prerequisites / Setup, Quick Reference and Core Concepts, plus 4 more sections
Reaches rpc.mainnet.arc.io and rpc.testnet.arc.io; needs PRIVATE_KEY

What it does

Use Arc is an agent skill from circlefin/skills. 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, Arc Mainnet, or Arc Testnet is mentioned, working with any…

Its SKILL.md is about 2.1k tokens, which your agent loads only when the skill is triggered. The skill folder holds 2 other files, including reference files (for example `references/deploying-on-arc.md`).

It sits in Backend & APIs, covering Smart contracts and Crypto and DeFi analysis. It works with Circle USDC, viem and wagmi and Ethereum. The repository describes itself as: Circle's open source skills for AI-assisted development. The licence is Apache-2.0.

When your agent uses it

Tasks that involve Smart contracts
Tasks that involve Crypto and DeFi analysis

Example prompts

“/use-arc”

Requirements

A credential in PRIVATE_KEY

Workflow steps

3 steps, taken from the first numbered list in SKILL.md.

Configure the chain — use the built-in viem chains (no custom definition needed): arcTestnet for testnet, arc for mainnet.
Deploy contracts — standard Foundry/Hardhat against ARC_TESTNET_RPC_URL (or ARC_MAINNET_RPC_URL), or Circle's Smart Contract Platform…
Bridge USDC in — Arc's CCTP domain is 26; use the bridge-stablecoin skill for the full workflow.

What it can do on your machine

Read from SKILL.md and the folder at commit 58ab864. It shows what the files ask for, not the result of running them.

Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md (its code samples are bash).
From the folder's file list and the shell code blocks in SKILL.md.
Network
Hosts in commands or code, which the agent is likely to contact:
- rpc.mainnet.arc.io
- rpc.testnet.arc.io
Also links to:
- faucet.circle.com
- explorer.arc.io
- explorer.testnet.arc.io
- docs.arc.io
- developers.circle.com
- console.circle.com
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names these keys or tokens, usually read from environment variables:
- PRIVATE_KEY
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Use Arc loads about 2.1k tokens when it runs, and up to ~2.5k if it reads all its reference files. Until then it costs about 193 tokens; SKILL.md has 902 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it: ~193
When it runs · the whole SKILL.md, loaded when a task matches: ~2.1k
With references · SKILL.md plus every file in references/, read only if the agent opens them: ~2.5k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check: notes

The automated check noted patterns worth knowing about, such as sudo or a known installer.

NoteMentions a .env fileSKILL.md:78

s manager. Add `.gitignore` entries for `.env*` and secret files when scaffolding.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from circlefin/skills at commit 58ab864, republished under its Apache-2.0 licence (© circlefin). 902 words, ~2,102 tokens.

Download SKILL.mdSave it as .claude/skills/use-arc/SKILL.md (or your agent's skills folder). This skill also uses 1 other file; get the full folder from GitHub.

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, Arc Mainnet, 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 Mainnet, 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

bash

ARC_MAINNET_RPC_URL=https://rpc.mainnet.arc.io
ARC_TESTNET_RPC_URL=https://rpc.testnet.arc.io
PRIVATE_KEY=         # Deployer wallet private key

Quick Reference

Network Details

Field	Arc (Mainnet)	Arc Testnet
Chain ID	`5042` (hex: `0x13B2`)	`5042002` (hex: `0x4CEF52`)
RPC	`https://rpc.mainnet.arc.io`	`https://rpc.testnet.arc.io`
WebSocket	`wss://rpc.mainnet.arc.io`	`wss://rpc.testnet.arc.io`
Explorer	https://explorer.arc.io	https://explorer.testnet.arc.io
Faucet	-- (fund with real USDC)	https://faucet.circle.com
CCTP Domain	`26`	`26`

Token Addresses for Arc

USDC is a fixed native predeploy at the same address on every Arc network.

Token	Decimals	Mainnet	Testnet
USDC	6 (ERC-20)	`0x3600000000000000000000000000000000000000`	`0x3600000000000000000000000000000000000000`
EURC	6	`0xbEf5f6d51CB62b58e6A8f77868681825C6fe21c1`	`0x89B50855Aa3bE2F677cD6303Cec089B5F319D72a`

For other tokens, see the Arc contract addresses page.

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.
Mainnet and testnet: Arc mainnet (chain ID 5042) and Arc testnet (chain ID 5042002) are both available — see Network Details for the config of each. Mainnet transactions move real USDC and are irreversible; use testnet for development and demos.
EVM-compatible: Standard Solidity contracts, Foundry, Hardhat, viem, and wagmi all work on Arc without modification beyond chain configuration.

Implementation Patterns

READ references/deploying-on-arc.md for the runnable setup — wagmi chain config, Foundry deploy, Circle's pre-audited contract templates, and bridging USDC in.

Configure the chain — use the built-in viem chains (no custom definition needed): arcTestnet for testnet, arc for mainnet.
Deploy contracts — standard Foundry/Hardhat against ARC_TESTNET_RPC_URL (or ARC_MAINNET_RPC_URL), or Circle's Smart Contract Platform templates (ERC-20/721/1155/Airdrop).
Bridge USDC in — Arc's CCTP domain is 26; use the bridge-stablecoin skill for the full 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.

Show full SKILL.md (398 more words)Show less

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 mainnet (arc) and Arc Testnet (arcTestnet) both ship in Viem -- no custom chain definition is required.
ALWAYS verify the user is on the intended Arc network (mainnet chain ID 5042 or testnet 5042002) before submitting transactions.
ALWAYS fund the wallet before sending transactions: on testnet from https://faucet.circle.com; on mainnet with real USDC.
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.
Arc mainnet moves real USDC and transactions are irreversible. Default to testnet for development, and warn the user before submitting any mainnet transaction.

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 (Mainnet)
Arc Explorer (Testnet)
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.

Files

SKILL.md and 1 other file (references) in plugins/circle/skills/use-arc of circlefin/skills.

SKILL.md
references/deploying-on-arc.md

Open the folder on GitHubat commit 58ab864

Compare with similar skills

Use Arc next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Use Arc compared with similar skills
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Payram Crypto PaymentsPayRam/payram-mcp	158	—	~2k	Automated safety check: Notes	None	today
Alchemy Agentic Gatewaymoonpay/skills	113	—	~2.1k	Automated safety check: Notes	MIT	27 days ago
AlchemyBankrBot/skills	1.2k	—	~3.5k	Automated safety check: Pass	MIT	3 days ago
Viemmajiayu000/claude-skill-registry	666	1 repos	~2.5k	Automated safety check: Pass	Apache-2.0	today
Deposit QrSuperior-Trade/superior-skills	214	1 repos	~1.1k	Automated safety check: Pass	MIT	28 days ago

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Works with

Questions about Use Arc

What does Use Arc do?

Provide instructions on how to build with Arc, Circle's blockchain where USDC is the native gas token. Use Arc is an agent skill from circlefin/skills. Provide instructions on how to build with Arc, Circle's blockchain where USDC is the native gas token.

When should I use Use Arc?

Use Arc fits situations like: tasks that involve Smart contracts; tasks that involve Crypto and DeFi analysis.

How do I install Use Arc in Claude Code?

Run `npx skills add circlefin/skills --skill use-arc -a claude-code`. Or copy the skill folder (plugins/circle/skills/use-arc in circlefin/skills) into .claude/skills/use-arc in your project. Claude Code loads it when a task matches its description.

How do I install Use Arc in Codex?

Run `npx skills add circlefin/skills --skill use-arc -a codex`. Or copy the skill folder (plugins/circle/skills/use-arc in circlefin/skills) into .agents/skills/use-arc in your project. Codex loads it when a task matches its description.

Can I use Use Arc in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add circlefin/skills --skill use-arc -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/use-arc, .gemini/skills/use-arc, .github/skills/use-arc and .opencode/skills/use-arc in your project.

What does Use Arc need to run?

Going by SKILL.md and its folder, Use Arc needs credentials named PRIVATE_KEY. Our summary lists: A credential in PRIVATE_KEY.

Does Use Arc access the network?

SKILL.md names 8 domains. In commands or code: rpc.mainnet.arc.io and rpc.testnet.arc.io; the agent is likely to contact these when it follows the instructions. As links in the text: faucet.circle.com, explorer.arc.io, explorer.testnet.arc.io, docs.arc.io, developers.circle.com and console.circle.com. This is read from the text; nothing was executed.

Is Use Arc safe to install?

Our automated static check of SKILL.md found notes only (mentions a .env file), nothing it rates as a warning. It is not a guarantee. Review the folder before installing.

What licence does Use Arc use?

Use Arc is published under the Apache-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Use Arc use?

About 2.1k tokens (SKILL.md is roughly 8.4k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 365 tokens, read only when the agent opens those files.

What are the alternatives to Use Arc?

Skills that share tags, products or a category with Use Arc: Payram Crypto Payments (PayRam/payram-mcp, 158 stars), Alchemy Agentic Gateway (moonpay/skills, 113 stars), Alchemy (BankrBot/skills, 1.2k stars) and Viem (majiayu000/claude-skill-registry, 666 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Use Arc?

circlefin (a GitHub organization) maintains it in circlefin/skills, which has 155 GitHub stars. The repository holds 18 skills in this directory. The repository was last updated on September 16, 2026.

Source: circlefin/skills on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.

Install Use Arc

Facts

At a glance

What it does

When your agent uses it

Example prompts

Requirements

Workflow steps

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Overview

Prerequisites / Setup

Wallet Funding

Environment Variables

Quick Reference

Network Details

Token Addresses for Arc

Core Concepts

Implementation Patterns

Rules

Security Rules

Best Practices

Next Steps

Reference Links

Files

Compare with similar skills

Similar skills

More from circlefin/skills

Related

Questions about Use Arc