> ## 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.

# CCTP Starknet contracts and interfaces

> Contracts for CCTP support on the Starknet blockchain

## Overview

Starknet CCTP contracts are written in Cairo and run on a non-EVM zk-rollup.
Transactions executed on Starknet are batched and proven using STARK proofs,
which are then posted to Ethereum L1. This design allows Starknet to inherit
Ethereum's security while offering higher throughput and lower fees.

To align with Starknet's architecture while keeping parity with EVM chains, CCTP
uses two contracts:

* `TokenMessengerMinterV2`: consolidates the responsibilities of
  `TokenMessengerV2` (burn + send) and `TokenMinterV2` (receive + mint).
* `MessageTransmitterV2`: provides the messaging layer that emits or receives
  attested messages and delivers them to `TokenMessengerMinterV2`.

This mirrors how other non-EVM deployments (for example, Solana) combine
messenger and minter logic while preserving behavior with the EVM equivalents.

For working end-to-end examples, see
[Transfer USDC between Starknet and Arc](/cctp/quickstarts/transfer-usdc-starknet-arc).

## Mainnet contract addresses

| Contract | [Domain](/cctp/cctp-supported-blockchains#cctp-supported-domains) | Address |
| :- | :- | :- |
| `TokenMessengerMinterV2` | 25 | [`0x07d421B9cA8aA32DF259965cDA8ACb93F7599F69209A41872AE84638B2A20F2a`](https://voyager.online/contract/0x07d421B9cA8aA32DF259965cDA8ACb93F7599F69209A41872AE84638B2A20F2a) |
| `MessageTransmitterV2` | 25 | [`0x02EBB5777B6dD8B26ea11D68Fdf1D2c85cD2099335328Be845a28c77A8AEf183`](https://voyager.online/contract/0x02EBB5777B6dD8B26ea11D68Fdf1D2c85cD2099335328Be845a28c77A8AEf183) |

## Testnet contract addresses

| Contract | [Domain](/cctp/cctp-supported-blockchains#cctp-supported-domains) | Address |
| :- | :- | :- |
| `TokenMessengerMinterV2` | 25 | [`0x04bDdE1E09a4B09a2F95d893D94a967b7717eB85A3f6dEcA8c080Ee01fBc3370`](https://sepolia.voyager.online/contract/0x04bDdE1E09a4B09a2F95d893D94a967b7717eB85A3f6dEcA8c080Ee01fBc3370) |
| `MessageTransmitterV2` | 25 | [`0x04db7926C64f1f32a840F3Fa95cB551f3801a3600Bae87aF87807A54DCE12Fe8`](https://sepolia.voyager.online/contract/0x04db7926C64f1f32a840F3Fa95cB551f3801a3600Bae87aF87807A54DCE12Fe8) |

## CCTP interface

* `TokenMessengerMinterV2`: initiates crosschain burns and mints tokens upon
  attested message receipt.
* `MessageTransmitterV2`: emits messages, verifies attestations, and routes
  verified messages to the recipient contract.

### TokenMessengerMinterV2 interface

The `TokenMessengerMinterV2` contract consolidates the roles of both
`TokenMessengerV2` and `TokenMinterV2` found on EVM chains. It handles USDC
burns, message emission, and token minting once crosschain messages are attested
by Circle's Iris service.

| Function | Description | Notes |
| :- | :- | :- |
| `deposit_for_burn` | Burns USDC and emits a crosschain message for minting on another domain. | Standard CCTP transfer initiation. |
| `deposit_for_burn_with_hook` | Same as `deposit_for_burn`, but attaches custom metadata (`hook_data`). | Used for programmable transfers. |
| `handle_receive_finalized_message` | Mints USDC upon receiving a fully finalized message. | Called by `MessageTransmitterV2`. |
| `handle_receive_unfinalized_message` | Processes partially finalized (“Fast Burn”) messages. | Enables faster crosschain transfers. |
| `message_body_version` | Returns supported message format version. | Used for compatibility checks. |
| `local_message_transmitter` | Returns the linked `MessageTransmitterV2` address. | Must match configured domain transmitter. |

### MessageTransmitterV2 interface

The `MessageTransmitterV2` contract provides the core messaging layer for CCTP
on Starknet. It is responsible for emitting, receiving, and validating
crosschain messages, enforcing attestation rules, and ensuring message
uniqueness.

| Function | Description | Notes |
| :- | :- | :- |
| `send_message` | Sends a crosschain message with specified domain, recipient, and message body. | Core function for outgoing CCTP messages. |
| `receive_message` | Validates a message and its attestation; delivers message body to the recipient. | Called by an offchain forwarding service with an attestation from Circle to complete the transfer. |
| `get_max_message_body_size` | Returns the maximum allowed message size. | Used by offchain components for validation. |
| `is_nonce_used` | Checks if a message nonce has been processed already. | Prevents message replay. |
| `get_local_domain` | Returns this contract's domain ID. | Expected to be 25 for Starknet. |
| `get_version` | Returns protocol version supported by this transmitter. | Used by Iris attestation service. |