> ## Documentation Index
> Fetch the complete documentation index at: https://developers.circle.com/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> Before reading these docs, install the relevant Circle Skill to get pre-loaded context — skills are LLM-optimized and cover architecture decisions, correct flows, and common pitfalls. 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. Available skills: use-usdc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-usdc/SKILL.md (balances, transfers, approvals on EVM and Solana); EURC has no skill — see https://developers.circle.com/stablecoins/what-is-eurc.md; bridge-stablecoin https://github.com/circlefin/skills/blob/master/plugins/circle/skills/bridge-stablecoin/SKILL.md (crosschain transfers via CCTP, USDC, EURC, and third-party assets); use-arc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-arc/SKILL.md (Arc chain config, contract deployment, USDC bridging — Arc docs: https://docs.arc.io/llms.txt); use-circle-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-circle-wallets/SKILL.md (choose wallet type); use-developer-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-developer-controlled-wallets/SKILL.md (custodial wallets for payouts and treasury); use-user-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-user-controlled-wallets/SKILL.md (embedded wallets with Web2 login); use-modular-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-modular-wallets/SKILL.md (smart contract wallets with passkeys and ERC-4337); use-gateway https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-gateway/SKILL.md (unified USDC balance, nanopayments); use-smart-contract-platform https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-smart-contract-platform/SKILL.md (deploy, interact, monitor contracts). Pair any skill with the Circle MCP server for live SDK signatures, contract addresses, and chain IDs: {"mcpServers":{"circle":{"url":"https://api.circle.com/v1/codegen/mcp"}}}.
> Read the product overview first. Each product has an overview explaining when and why to use it. Read it before quickstarts.
> Pick the right wallet type. Developer-controlled (you hold keys), user-controlled (end user holds keys via PIN/social login), or modular (smart contract wallets with passkeys). See https://developers.circle.com/wallets.md.
> Use CCTP V2 for crosschain transfers. CCTP natively transfers USDC and EURC via burn-and-mint, and supports permissionless wrapping of third-party assets via lock-and-mint. V1 is legacy; always use V2 unless V1 is specified or the chain requires it (Noble, Sui, and Aptos still require V1). Migration guide: https://developers.circle.com/cctp/migration-from-v1-to-v2.md.
> Use Bridge Kit for frontend bridging. Wraps CCTP with a simpler SDK for user-facing apps. Use CCTP directly for backend transfers.
> Gas Station vs Paymaster. Gas Station sponsors gas for Circle Wallet transactions. Paymaster lets users pay gas in USDC. Different use cases — read both overviews.
> Gateway Nanopayments for sub-cent payments. Gasless USDC micropayments down to $0.000001 via x402 and batched settlement. For pay-per-request APIs, AI agent payments, streaming.
> Look up USDC addresses per chain. Never hardcode — use https://developers.circle.com/stablecoins/usdc-contract-addresses.md.
> Prefer SDKs over raw API calls. Node.js and Python SDKs handle auth, retries, and errors.
> API key required. Bearer token in Authorization header. Testnet and mainnet use separate keys and may use different base URLs depending on the product.
> Set up webhooks when available. Most operations are async. Webhooks deliver transaction confirmations and state changes.
> When calling list endpoints, paginate using pageSize and pageAfter until no nextPageAfter cursor is returned—stopping at the first page silently misses records.
> Building an AI agent? Start with the Agent Stack—Circle CLI, agent wallets, and nanopayments built for autonomous use cases: https://developers.circle.com/agent-stack.md.

# Transfer USDC on testnet from Ethereum to Avalanche using CCTP V1

> Explore this script to transfer USDC on testnet between two EVM-compatible chains via CCTP V1

<Warning>
  **This is CCTP V1 version. For the latest version, see [CCTP](/cctp)**.
</Warning>

This guide demonstrates how to use the [viem](https://viem.sh/) framework and
the [CCTP V1 API](/cctp/v1/cctp-apis) in a simple script that enables a user to
transfer USDC from a wallet address on the **Ethereum Sepolia testnet** to
another wallet address on the **Avalanche Fuji testnet**.

To get started with CCTP V1, follow the example script provided
[on GitHub](https://github.com/circlefin/evm-cctp-contracts/blob/d1c24577fb627b08483dc42e4d8a37a810b369f7/docs/index.js).
The example uses
[web3.js](https://web3js.readthedocs.io/en/v1.8.1/getting-started.html) to
transfer USDC from a wallet address on Ethereum Sepolia testnet to another
wallet address on Avalanche Fuji testnet.

The script has five steps:

1. In this first step, you initiate a transfer of USDC from one blockchain to
   another, and specify the recipient wallet address on the destination chain.
   This step approves the Ethereum Sepolia **TokenMessenger** contract to
   withdraw USDC from the provided Ethereum Sepolia wallet address.

```javascript JavaScript theme={null}
const approveTx = await usdcEthContract.methods
  .approve(ETH_TOKEN_MESSENGER_CONTRACT_ADDRESS, amount)
  .send({ gas: approveTxGas });
```

2. In this second step, you facilitate a burn of the specified amount of USDC on
   the source chain. This step executes the `depositForBurn` function on the
   Ethereum Sepolia **TokenMessenger** contract deployed on
   [Sepolia testnet](https://sepolia.etherscan.io/address/0x9f3B8679c73C2Fef8b59B4f3444d4e156fb70AA5).

```javascript JavaScript theme={null}
const burnTx = await ethTokenMessengerContract.methods
  .depositForBurn(
    amount,
    AVAX_DESTINATION_DOMAIN,
    destinationAddressInBytes32,
    USDC_ETH_CONTRACT_ADDRESS,
  )
  .send();
```

3. In this third step, you make sure you have the correct message and hash it.
   This step extracts `messageBytes` emitted by the **MessageSent** event from
   `depositForBurn` transaction logs and hashes the retrieved `messageBytes`
   using the **keccak256** hashing algorithm.

```javascript JavaScript theme={null}
const transactionReceipt = await web3.eth.getTransactionReceipt(
  burnTx.transactionHash,
);
const eventTopic = web3.utils.keccak256("MessageSent(bytes)");
const log = transactionReceipt.logs.find((l) => l.topics[0] === eventTopic);
const messageBytes = web3.eth.abi.decodeParameters(["bytes"], log.data)[0];
const messageHash = web3.utils.keccak256(messageBytes);
```

4. In this fourth step, you request the attestation from Circle, which provides
   authorization to mint the specified amount of USDC on the destination chain.
   This step polls the attestation service to acquire the signature using the
   `messageHash` from the previous step.

<Note>
  **Rate Limit**

  The attestation service rate limit is 35 requests per second. If you exceed 35
  requests per second, the service blocks all API requests for the next 5 minutes
  and returns an HTTP 429 response.
</Note>

```javascript JavaScript theme={null}
let attestationResponse = { status: "pending" };
while (attestationResponse.status != "complete") {
  const response = await fetch(
    `https://iris-api-sandbox.circle.com/attestations/${messageHash}`,
  );
  attestationResponse = await response.json();
  await new Promise((r) => setTimeout(r, 2000));
}
```

5. In this final step, you enable USDC to be minted on the destination chain.
   This step calls the `receiveMessage` function on the Avalanche Fuji
   **MessageTransmitter** contract to receive USDC at the Avalanche Fuji wallet
   address.

```javascript JavaScript theme={null}
const receiveTx = await avaxMessageTransmitterContract.receiveMessage(
  receivingMessageBytes,
  signature,
);
```

You have successfully transferred USDC between two EVM-compatible chains using
CCTP V1 end-to-end.