> ## 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.

# Install the App Kit SDK

> Install the App Kit SDK and your preferred adapter to start building apps

Installing the App Kit SDK gives you every capability (Send, Bridge, Swap,
Unified Balance, Onramp, Earn, and Borrow) in a single package. To get started,
install the latest version and the adapter that fits your environment.

<Note>
  An [API key](https://developers.circle.com/api-reference/keys) from the
  [Circle Console](https://console.circle.com/api-keys) is required for
  [Onramp](/app-kit/onramp) and for configuring a
  [Borrow integrator fee](/app-kit/howtos/borrow/configure-integrator-fee). It's
  optional for [Swap](/app-kit/swap), [Earn](/app-kit/earn), and
  [Borrow](/app-kit/borrow), but using one gives you higher rate limits.
</Note>

<Steps>
  <Step title="Install the core package">
    <CodeGroup>
      ```bash npm theme={null}
      npm install @circle-fin/app-kit
      ```

      ```bash yarn theme={null}
      yarn add @circle-fin/app-kit
      ```
    </CodeGroup>

    <Accordion icon="circle-info" title="Need a lighter install? Individual App Kits are available">
      The App Kit SDK includes every capability in a single package. Or, install kits individually:

      <Tabs>
        <Tab title="Bridge Kit">
          <CodeGroup>
            ```bash npm theme={null}
            npm install @circle-fin/bridge-kit
            ```

            ```bash yarn theme={null}
            yarn add @circle-fin/bridge-kit
            ```
          </CodeGroup>
        </Tab>

        <Tab title="Swap Kit">
          <CodeGroup>
            ```bash npm theme={null}
            npm install @circle-fin/swap-kit
            ```

            ```bash yarn theme={null}
            yarn add @circle-fin/swap-kit
            ```
          </CodeGroup>
        </Tab>

        <Tab title="Unified Balance Kit">
          <CodeGroup>
            ```bash npm theme={null}
            npm install @circle-fin/unified-balance-kit
            ```

            ```bash yarn theme={null}
            yarn add @circle-fin/unified-balance-kit
            ```
          </CodeGroup>
        </Tab>

        <Tab title="Onramp Kit">
          <CodeGroup>
            ```bash npm theme={null}
            npm install @circle-fin/onramp-kit
            ```

            ```bash yarn theme={null}
            yarn add @circle-fin/onramp-kit
            ```
          </CodeGroup>
        </Tab>

        <Tab title="Earn Kit">
          <CodeGroup>
            ```bash npm theme={null}
            npm install @circle-fin/earn-kit
            ```

            ```bash yarn theme={null}
            yarn add @circle-fin/earn-kit
            ```
          </CodeGroup>
        </Tab>

        <Tab title="Borrow Kit">
          <CodeGroup>
            ```bash npm theme={null}
            npm install @circle-fin/borrow-kit
            ```

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

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

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

      <Tab title="Ethers">
        <CodeGroup>
          ```bash npm theme={null}
          npm install @circle-fin/adapter-ethers-v6 ethers
          ```

          ```bash yarn theme={null}
          yarn add @circle-fin/adapter-ethers-v6 ethers
          ```
        </CodeGroup>
      </Tab>

      <Tab title="Solana">
        <CodeGroup>
          ```bash npm theme={null}
          npm install @circle-fin/adapter-solana-kit @solana/kit @solana/web3.js
          ```

          ```bash yarn theme={null}
          yarn add @circle-fin/adapter-solana-kit @solana/kit @solana/web3.js
          ```
        </CodeGroup>

        If bridging, you should also install an EVM adapter (Viem or Ethers).

        <Note>
          For the [Bridge tokens across blockchains](/app-kit/quickstarts/bridge-tokens-across-blockchains#solana) quickstart
          and [adapter setup](/app-kit/tutorials/adapter-setups#solana) examples, the same
          adapter is used with `@solana/kit` and `@solana/web3.js`.
        </Note>
      </Tab>

      <Tab title="Circle Wallets">
        <Badge color="blue">server-side only</Badge>

        If you have a [Circle Wallets](https://developers.circle.com/wallets) account, you can use the Circle Wallets adapter to
        connect to developer-controlled wallets and Circle Contracts.

        <CodeGroup>
          ```bash npm theme={null}
          npm install @circle-fin/adapter-circle-wallets
          ```

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