> ## 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.

# App Kit SDK: Borrow

> Originate and manage cirBTC-collateralized USDC loans on Arc with the App Kit SDK's Borrow capability

The [App Kit SDK](/app-kit) includes the Borrow capability, which lets your
users borrow USDC against cirBTC collateral without you integrating with a
lending protocol yourself. Your users post cirBTC, borrow USDC, and repay to
reclaim their collateral.

## How it works

A user supplies cirBTC as collateral and receives USDC in return, all in a
single atomic transaction on Arc. If you subscribe to
[webhooks](/app-kit/howtos/borrow/monitor-a-loan#subscribe-to-health-updates),
the SDK posts events when a loan's health changes, so you can prompt the user to
act before liquidation.

```mermaid theme={null}
flowchart LR
  U[User wallet] -->|"cirBTC collateral"| L[(Loan)]
  L -->|"USDC"| U
  L -->|"webhook events"| Y[Your backend]
```

For how loan health is measured and when a position becomes liquidatable, see
[How loan health works](/app-kit/concepts/borrow-loan-health).

## Quick look

This code snippet opens a loan by borrowing 1,000 USDC against cirBTC on Arc
Testnet:

```typescript TypeScript theme={null}
const result = await kit.borrow.borrow({
  from: { adapter: viemAdapter, chain: "Arc_Testnet" },
  marketId:
    "0x1111111111111111111111111111111111111111111111111111111111111111",
  borrowAmount: "1000.0",
});
```

For a complete end-to-end flow, follow the
[Originate a loan](/app-kit/quickstarts/originate-a-loan) quickstart.

## Installation

[Install the App Kit SDK](/app-kit/tutorials/installation) to use Borrow. If you
only need to borrow and don't want to install the full App Kit SDK, install the
standalone Borrow Kit for your preferred adapter:

<Info>
  Borrow writes require an adapter with atomic-batch support. Use Viem or Circle
  Wallets.
</Info>

<Tabs>
  <Tab title="Viem">
    <CodeGroup>
      ```bash npm theme={null}
      npm install @circle-fin/borrow-kit @circle-fin/adapter-viem-v2 viem
      ```

      ```bash yarn theme={null}
      yarn add @circle-fin/borrow-kit @circle-fin/adapter-viem-v2 viem
      ```
    </CodeGroup>
  </Tab>

  <Tab title="Circle Wallets">
    <CodeGroup>
      ```bash npm theme={null}
      npm install @circle-fin/borrow-kit @circle-fin/adapter-circle-wallets
      ```

      ```bash yarn theme={null}
      yarn add @circle-fin/borrow-kit @circle-fin/adapter-circle-wallets
      ```
    </CodeGroup>
  </Tab>
</Tabs>