> ## 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.

# Wallet provider compatibility

CPN allows you to bring your own wallet provider when integrating with the
network. Circle Wallets is an option for your integration, but not a
requirement. When bringing your own wallet provider, you should make sure that
they support the features and signing methods that are required to interact with
CPN.

## Requirements

The following features and signing methods are required for a wallet provider to
be able to integrate with CPN:

* **Custodial wallet support:** The provider must be able to sign transactions
  for wallets without requiring user interaction.
* **EIP-712 signing:** The provider must support EIP-712 typed data. The
  resulting signature can be used in one of the following ways:
  * The signature can be verified by recovering the signer's address with the
    hash of the typed data (on behalf of an EOA).
  * The signature can be validated by the `isValidSignature` method defined in
    EIP-1271 with the hash of the typed data (on behalf of an SCA).

<Note>
  **Note:** USDC implements EIP-3009 with the EIP-7598 extension, enabling both
  EOAs and SCAs to authorize transfers via the EIP-3009 mechanism.
</Note>

* SCA wallet interface: When using an SCA wallet as the sender wallet, the
  wallet contract must implement the following two interfaces:
  * EIP-165 Standard Interface Detection: The SCA wallet must correctly
    implement the EIP-165 interface detection standard. The `supportsInterface`
    function must return `true` for the EIP-1271 interface ID.
  * EIP-1271 Standard Signature Validation for Contracts: The SCA wallet must
    correctly implement the EIP-1271 interface, which defines the
    `isValidSignature` function.

* **Solana signing:** The provider must support signing raw Solana transaction
  using `Ed25519`, without broadcasting them to the blockchain. The provider
  must also support
  [partial signing](https://solana.com/developers/cookbook/transactions/offline-transactions#partial-sign-transaction)
  of the transaction.

* **Solana memo field:** The provider must support a memo field for Solana
  transactions.

| Blockchain | Required signing methods |
| - | - |
| EVM | EIP-712 typed data signing |
| Solana | Solana transaction signing (partial signing) |

<Note>
  Arc is an EVM-compatible blockchain, so the EVM row applies. Your wallet
  provider must support EIP-712 typed data signing.

  Arc uses USDC as gas through its native paymaster. Operational wallets on Arc
  don't need to hold a separate native gas token (no ETH funding required).
</Note>