> ## 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. # How upfront fees work > Learn how CCTP collects upfront fees and completes Fast Transfer and Forwarding Service transfers. Paying fees upfront starts with requesting a signed fee quote from Circle, then submitting that quote with the burn in a single transaction on the source blockchain. Circle honors the quoted price, so the recipient receives the full transferred amount. For a full walkthrough, see [Transfer USDC with upfront fees](/cctp/howtos/transfer-usdc-with-upfront-fees). ## Transfer flow with upfront fees ```mermaid theme={null} sequenceDiagram actor User participant API as Quote API participant USDC as USDC token participant TMWF as TokenMessengerWithFees participant CCTP as TokenMessengerV2 participant Circle as Circle User->>API: Request fee quote API-->>User: Signed, time-bound quote User->>USDC: approve(TMWF, amount [+ fee]) User->>TMWF: depositForBurnWithFees (quote + fee) TMWF->>TMWF: Verify quote and collect fee TMWF->>CCTP: depositForBurn CCTP-->>Circle: Burn message emitted Circle-->>User: Full amount minted on destination ``` Request an [upfront fee quote](/cctp/concepts/upfront-fee-quotes) from the [Quote API](/api-reference/cctp/all/create-usdc-burn-quote) for the fees you want to pay upfront: the Forwarding Service fee, the Fast Transfer fee, or both. See [Paying the fee](#paying-the-fee) for the available fee tokens. Circle returns a signed, time-bound quote that prices each fee and includes a `signedQuote` blob. Approve [`TokenMessengerWithFees`](/cctp/references/contract-interfaces#tokenmessengerwithfees) to spend the USDC amount you're transferring, plus the quoted fee if you're paying it in USDC. The contract pulls the transfer amount for the burn and, if applicable, the fee amount. Call `depositForBurnWithFees` (or `depositForBurnWithHookAndFees`) on `TokenMessengerWithFees`, passing the signed quote along with the standard `depositForBurn` parameters, and pay the quoted fee amount: attach it as the transaction's native value, or rely on the USDC approval from the previous step. The contract verifies the quote, collects the fee, and then delegates to `TokenMessengerV2` to complete the CCTP burn. Circle attests the transfer with no fee deducted at mint, and the full amount is minted to the recipient. ## Paying the fee The token you selected on the quote request decides where the fee comes from: * **Native gas token** (default): attach the quoted amount as the transaction's native value. * **USDC**: request the quote with `feeToken` set to the USDC address, then approve `TokenMessengerWithFees` to spend the quoted fee before you submit. This fee approval is on top of the USDC you're transferring, so approve the transfer amount plus the quoted fee. ## Forwarding with upfront fees When a quote includes a `FORWARD` fee, the transfer is forwarded on the destination blockchain the same way as any other [Forwarding Service](/cctp/concepts/forwarding-service) transfer, except that the forwarding fee isn't deducted from the transferred amount. What changes is how you supply the hook data. Forwarding requires a valid `cctp-forward` hook in the submitted hook data. [`depositForBurnWithFees`](/cctp/references/contract-interfaces#depositforburnwithfees) builds this hook for you automatically, as long as you request the quote without passing `hookData`. For custom hook data, use [`depositForBurnWithHookAndFees`](/cctp/references/contract-interfaces#depositforburnwithhookandfees) and submit the same `hookData` you used to request the quote. For the hook structure, including how to append your own frame, see [Forwarding Service hook format](/cctp/concepts/forwarding-service#hook-format).