> ## Documentation Index > Fetch the complete documentation index at: https://docs.arc.io/llms.txt > Use this file to discover all available pages before exploring further. > ## Agent Instructions > Before reading these docs, install the Circle Skill for Arc to get pre-loaded context: use-arc (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-arc/SKILL.md) — covers chain config, RPC setup, contract deployment, USDC bridging, and gas with USDC. In Claude Code: run /plugin marketplace add circlefin/skills then /plugin install circle-skills@circle. With Vercel Skills CLI: run npx skills add circlefin/skills. > USDC is the gas token. Arc uses USDC for gas fees, not ETH. Configure gas payment in USDC when submitting transactions. > Read EVM differences before writing Arc code. Arc targets the Osaka EVM baseline. Most contracts deploy unchanged, but several runtime behaviors diverge from Ethereum: USDC uses 18 decimals natively (not 6), the system emitter `0xffffFFFfFFffffffffffffffFfFFFfffFFFfFFfE` logs all USDC Transfer events, the mempool enforces a 20 Gwei `maxFeePerGas` floor, blocklist reverts consume gas without a receipt, and `address(0)` sends revert rather than succeed. https://docs.arc.io/arc/references/evm-differences.md is the canonical reference for all Arc-specific runtime behaviors. Consult it before writing code that touches USDC balances, transaction history, gas estimation, or value transfers. > Sub-second finality. Transactions are final in under 1 second. No need to wait for multiple block confirmations. > Use App Kits for multichain payment and liquidity capabilities. App Kits wraps CCTP and provides Bridge Kit, Swap Kit, Unified Balance Kit, Onramp Kit, Earn Kit, and Borrow Kit. Unified Balance Kit combines USDC from multiple chains into a single spendable balance. Earn Kit integrates earn opportunities into your app. Borrow Kit lets users borrow USDC against cirBTC collateral on Arc. > Use Arc Foundry for contract development. Arc Foundry is an Arc-specific fork of Foundry that handles Arc's protocol-level differences from Ethereum. It provides arc-forge, arc-cast, and arc-anvil. Install it before deploying contracts: https://docs.arc.io/arc/tutorials/install-arc-foundry.md. > Arc is available on both Testnet and Mainnet. See https://docs.arc.io/arc/references/connect-to-arc.md for RPC endpoints and https://faucet.circle.com for testnet tokens. > Always check Contract Addresses: https://docs.arc.io/arc/references/contract-addresses.md > Building beyond Arc? Circle offers skills for the full platform: use-usdc (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-usdc/SKILL.md), use-circle-wallets (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-circle-wallets/SKILL.md), use-developer-controlled-wallets (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-developer-controlled-wallets/SKILL.md), use-user-controlled-wallets (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-user-controlled-wallets/SKILL.md), use-modular-wallets (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-modular-wallets/SKILL.md), use-gateway (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-gateway/SKILL.md), use-smart-contract-platform (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-smart-contract-platform/SKILL.md). Full Circle developer docs: https://developers.circle.com/llms.txt. # Troubleshoot Arc Studio > Fix Arc Studio errors, usage limits, and connection problems. Match the message or behavior you see to its likely cause and fix. If a fix doesn't work, contact [Circle Support](https://support.circle.com/) or ask in the [Arc Discord](https://discord.com/invite/buildonarc). In the CLI, run [`arc-studio doctor`](https://docs.arc.io/ai/arc-studio-cli#commands) and include its output. ## Usage and app limits | Message or behavior | Cause | Fix | | - | - | - | | "You've reached your daily limit" or "30-day usage limit" | Your AI usage has reached its daily or 30-day limit. A daily limit resets. A 30-day limit covers a rolling 30 days. | Wait and try again. In the CLI, run [`arc-studio usage`](https://docs.arc.io/ai/arc-studio-cli#commands) to see how much you've used. To raise your organization's limit, run [`arc-studio upgrade`](https://docs.arc.io/ai/arc-studio-cli#commands), which opens a checkout. Only billing admins can pay. | | "Thread limit reached" | Each app has a limit on conversation threads. | Delete an old thread in Arc Studio on the web, then start a new one. | | You can't open or start a new app | You've reached the limit on apps running at once. The CLI reports a 429 `active-sandbox-limit` error. | Pause an app with [`arc-studio pause --app `](https://docs.arc.io/ai/arc-studio-cli#commands), using an ID from `arc-studio apps`, or delete one. | ## Service and sandbox | Message or behavior | Cause | Fix | | - | - | - | | "Sandbox is temporarily unavailable" or "Service temporarily unavailable" | A temporary service issue. | Wait a few minutes and try again. | | The sandbox is slow to load | Idle sandboxes pause after about 30 minutes. | None needed. Resuming takes 5 to 15 seconds, and the agent reconnects automatically. | ## GitHub and repositories | Message or behavior | Cause | Fix | | - | - | - | | "Your GitHub authorization expired" | Your GitHub authorization is no longer valid. | Disconnect and reconnect your GitHub account in Arc Studio on the web. | | "GitHub not connected" | Private repositories and pushing code to any repository require a connected account. Public repositories import without one. | Connect your GitHub account in Arc Studio on the web. | | "Clone failed" | The URL is wrong, or the repository doesn't exist or is private. Arc Studio can't tell a private repository from a missing one. | Check the URL. The CLI clones only public repositories, so connect GitHub in Arc Studio on the web to import a private one. If the CLI stops because the target directory has uncommitted changes, rerun with [`--force`](https://docs.arc.io/ai/arc-studio-cli#repository-clones) to overwrite it. | ## Deploys and transactions | Message or behavior | Cause | Fix | | - | - | - | | Netlify or Hugging Face deploy errors | The connection has expired or is missing. | Reconnect the integration in Arc Studio on the web. | | A transaction never appears and shows no error | Arc silently drops transactions with a `maxFeePerGas` lower than 20 Gwei. | Set `maxFeePerGas` to at least 20 Gwei. See [EVM differences](https://docs.arc.io/arc/references/evm-differences.md). | ## CLI turn outcomes A turn is one prompt and the agent's response to it. For all outcomes, see [Turn outcomes and exit codes](https://docs.arc.io/ai/arc-studio-cli.md#turn-outcomes-and-exit-codes). For an `error` turn, check the [`errorMessage`](https://docs.arc.io/ai/arc-studio-cli#result-document) field. | Status | Exit code | Cause | Fix | | - | - | - | - | | `needs_input` | 3 | The agent has questions. | Rerun against the same session with `--answers-json`. See [Answering follow-up questions](https://docs.arc.io/ai/arc-studio-cli.md#answering-follow-up-questions). | | `budget_exceeded` | 4 | Your daily or 30-day usage limit is spent (`monthly` in `budget.period`). | Run `arc-studio usage` to see which limit you've reached. Wait for it to reset, or run `arc-studio upgrade` to raise it (billing admins only). |