> ## 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.

# Quickstart: Swap tokens across blockchains

> Use the App Kit SDK to swap one token on the source blockchain and receive a different token on a destination blockchain in a single call

This quickstart walks you through how to use the App Kit SDK's
[Swap](/app-kit/swap) capability to swap tokens across blockchains in a single
call. The example swaps 1.00 USDC on Base for native POL delivered to a wallet
on Polygon.

Swap requires a kit key from the [Circle Console](https://console.circle.com/)
and is intended for server-side applications, but it is not specific to Circle
Wallets; you can use any compatible EVM adapter with
[supported tokens or blockchains](/app-kit/references/supported-blockchains).

<Note>
  If your Circle Wallet is a smart contract account (SCA), set
  `allowanceStrategy: "approve"`. USDC permit signatures use `ecrecover`, which
  does not accept the SCA's ERC-1271 signature, so the SDK uses an onchain
  `approve`.
</Note>

## Prerequisites

Before you begin, ensure that you've:

* Installed [Node.js v22+](https://nodejs.org/).
* Obtained the following from the
  [Circle Console](https://developers.circle.com/w3s/circle-developer-account):
  * [API Key](https://developers.circle.com/api-reference/keys#creating-an-api-key-for-developer-services)
  * [Entity secret](https://developers.circle.com/wallets/dev-controlled/register-entity-secret)
  * [Kit Key](https://developers.circle.com/api-reference/keys#kit-keys)
* Created a developer-controlled wallet on Base.
* Funded your Base wallet with USDC for the swap amount and ETH for gas.

## Step 1. Set up the project

### 1.1. Create the project and install dependencies

Create a new directory and install the App Kit SDK with the Circle Wallets
adapter and supporting tools:

```bash Shell theme={null}
# Set up your directory and initialize a Node.js project
mkdir app-kit-swap-crosschain-circle-wallets
cd app-kit-swap-crosschain-circle-wallets
npm init -y
npm pkg set type=module

# Set up module type and start command
npm pkg set scripts.start="tsx --env-file=.env index.ts"

# Install runtime dependencies
npm install @circle-fin/app-kit @circle-fin/adapter-circle-wallets tsx

# Install dev dependencies
npm install --save-dev typescript @types/node
```

<Tip>
  Only need to swap and want a lighter install than the full App Kit SDK? Install
  the standalone Swap Kit instead: `@circle-fin/swap-kit`.

  For server-side scripts, you can use any compatible EVM adapter, including the
  private key adapter. Keep private keys on the server and configure the adapter
  in the [wallet adapter setup guide](/app-kit/tutorials/adapter-setups).
</Tip>

### 1.2. Configure TypeScript (optional)

<Info>
  This step is optional. It helps prevent missing types in your IDE or editor.
</Info>

Create a `tsconfig.json` file:

```bash Shell theme={null}
npx tsc --init
```

Then, update the `tsconfig.json` file:

```bash Shell theme={null}
cat <<'EOF' > tsconfig.json
{
  "compilerOptions": {
    "target": "ESNext",
    "module": "ESNext",
    "moduleResolution": "bundler",
    "strict": true,
    "types": ["node"]
  }
}
EOF
```

### 1.3. Set environment variables

Create an `.env` file in the project directory:

```bash Shell theme={null}
touch .env
```

Add your server-side credentials. Replace `YOUR_API_KEY` with your Circle
Developer API key, `YOUR_ENTITY_SECRET` with your entity secret, and
`YOUR_KIT_KEY` with your kit key from the Circle Console:

```text .env theme={null}
CIRCLE_API_KEY=YOUR_API_KEY
CIRCLE_ENTITY_SECRET=YOUR_ENTITY_SECRET
KIT_KEY=YOUR_KIT_KEY
```

<Tip>
  Edit `.env` files in your IDE or editor so credentials are not leaked to your
  shell history.
</Tip>

## Step 2. Swap tokens

Create a script that estimates the route, submits the source-chain swap, waits
for crosschain delivery, and prints the final swap status.

<Note>
  Unlike same-chain swaps, crosschain swaps return immediately with
  `progress.status: 'PENDING'`. The destination-chain leg lands shortly after. Use
  `kit.waitForSwap()` to poll until the swap reaches a terminal status: `DONE`,
  `FAILED`, or `NOT_FOUND`.
</Note>

### 2.1. Create the script

Create an `index.ts` file in the project directory and add the following code.
This code swaps 1.00 USDC on Base for native POL delivered to your wallet on
Polygon.

Replace `YOUR_SOURCE_WALLET_ADDRESS` with your Base wallet address and
`YOUR_RECIPIENT_ADDRESS` with your Polygon recipient address. The recipient
address does not need POL to receive the swapped tokens.

<Info>
  Using other [tokens](/app-kit/references/supported-blockchains#supported-tokens)
  or [blockchains](/app-kit/references/supported-blockchains)? Change the source
  `chain`, `tokenIn`, `tokenOut`, `to.chain`, and `recipientAddress` values in
  `swapParams`. Both blockchains must support crosschain swap.
</Info>

```typescript TypeScript theme={null}
import { AppKit } from "@circle-fin/app-kit";
import { createCircleWalletsAdapter } from "@circle-fin/adapter-circle-wallets";
import type { SwapParams } from "@circle-fin/app-kit";

const kit = new AppKit();

const sourceWalletAddress = "YOUR_SOURCE_WALLET_ADDRESS";
const recipientAddress = "YOUR_RECIPIENT_ADDRESS";

const adapter = createCircleWalletsAdapter({
  apiKey: process.env.CIRCLE_API_KEY!,
  entitySecret: process.env.CIRCLE_ENTITY_SECRET!,
});

const swapParams: SwapParams = {
  from: {
    adapter,
    chain: "Base",
    address: sourceWalletAddress,
  },
  tokenIn: "USDC",
  tokenOut: "NATIVE",
  amountIn: "1",
  to: {
    chain: "Polygon",
    recipientAddress,
  },
  config: {
    kitKey: process.env.KIT_KEY!,
    allowanceStrategy: "approve",
  },
};

const estimate = await kit.estimateSwap(swapParams);
console.dir({ estimate }, { depth: null, colors: true });

const result = await kit.swap(swapParams);
console.dir({ result }, { depth: null, colors: true });

const status = await kit.waitForSwap({
  result,
  kitKey: process.env.KIT_KEY!,
});

console.dir({ status }, { depth: null, colors: true });
```

<Tip>
  Customize your crosschain swaps to
  [collect a custom fee](/app-kit/tutorials/swap/collect-swap-fee), or set a
  [slippage tolerance or stop limit](/app-kit/tutorials/swap/set-slippage-tolerance-or-stop-limit).
</Tip>

### 2.2. Run the script

Save the `index.ts` file and run the script in your terminal:

```bash Shell theme={null}
npm run start
```

<Note>
  Providers enforce route-specific minimum amounts. If `estimateSwap()` throws a
  `KitError` with code `INPUT_AMOUNT_OUT_OF_RANGE`, increase `amountIn` and
  estimate again (inside a `try`/`catch`) before calling `swap()`.
</Note>

### 2.3. Verify the transactions

After the script finishes, find the returned status object in the terminal
output:

* Use the source `txHash` and `chainIn` to verify the source-chain swap on the
  Base block explorer.
* Use `status.destination.txHash` to verify the destination-chain delivery on
  the Polygon block explorer.

The following is an example of how the estimate, result, and final status might
look in the terminal output. Values vary by route, liquidity, and gas price.

<CodeGroup>
  ```shell Estimate theme={null}
  {
    estimate: {
      tokenIn: 'USDC',
      tokenOut: 'NATIVE',
      amountIn: '1',
      chainIn: 'Base',
      chainOut: 'Polygon',
      fromAddress: '0xabcd...1234',
      toAddress: '0xabcd...1234',
      stopLimit: { amount: '12.1427586417541', token: 'NATIVE' },
      estimatedOutput: { amount: '12.518307878097', token: 'NATIVE' },
      fees: [
        { token: 'USDC', amount: '0.0002', type: 'provider' },
        { token: 'ETH', amount: '0.000010429566703815', type: 'gas' }
      ]
    }
  }
  ```

  ```shell Result theme={null}
  {
    result: {
      tokenIn: 'USDC',
      tokenOut: 'NATIVE',
      chainIn: 'Base',
      chainOut: 'Polygon',
      chain: 'Base',
      amountIn: '1.0',
      fromAddress: '0xabcd...1234',
      toAddress: '0xabcd...1234',
      txHash: '0x2f11...025e',
      explorerUrl: 'https://basescan.org/tx/0x2f11...025e',
      fees: [{ token: 'USDC', amount: '0.0002', type: 'provider' }],
      config: { allowanceStrategy: 'approve' },
      progress: { status: 'PENDING' }
    }
  }
  ```

  ```shell Final status theme={null}
  {
    status: {
      progress: {
        status: 'DONE',
        substatus: 'COMPLETED',
        substatusMessage: 'The transfer is complete.'
      },
      source: {
        txHash: '0x2f11...025e'
      },
      destination: {
        txHash: '0xd824...e331',
        token: {
          symbol: 'POL',
          address: '0x0000000000000000000000000000000000000000'
        },
        amount: '12.534043097347965275'
      }
    }
  }
  ```
</CodeGroup>