> ## 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-to: Use nanopayments with x402 > Add gas-free nanopayments alongside your existing x402 onchain payment flows Gateway Nanopayments integrates with existing x402 setups at every layer of the stack. It is **additive**: it introduces gas-free payments as a new option alongside standard onchain x402 payments, without replacing them. Sellers automatically accept both methods, and buyers choose whichever they have funded. ## Install the SDK ```shell theme={null} npm install @circle-fin/x402-batching ``` ## Integration paths Choose the guides that match your role in the x402 ecosystem. Add nanopayments to your x402 client so it can pay gas-free when servers support it Add gas-free nanopayments to your existing x402 server alongside your current payment flows Route Gateway payments alongside onchain payments in your facilitator service ### Seller (server-side) Add `BatchFacilitatorClient` and `GatewayEvmScheme` to your existing server. Your `402` responses then include both standard and Gateway payment options: ```ts theme={null} import { x402ResourceServer } from "@x402/express"; import { HTTPFacilitatorClient } from "@x402/core/server"; import { BatchFacilitatorClient, GatewayEvmScheme, } from "@circle-fin/x402-batching/server"; const server = new x402ResourceServer([ new HTTPFacilitatorClient({ url: "https://facilitator.example.com" }), new BatchFacilitatorClient(), ]); server.register("eip155:*", new GatewayEvmScheme()); await server.initialize(); ``` See [Full seller integration guide](/gateway-nanopayments/howtos/x402-seller). ### Buyer (client-side) Use `CompositeEvmScheme` to handle both Gateway and standard payments automatically. The client picks the right scheme based on what the server offers: ```ts theme={null} import { ExactEvmScheme } from "@x402/evm/exact/client"; import { CompositeEvmScheme, BatchEvmScheme, } from "@circle-fin/x402-batching/client"; const composite = new CompositeEvmScheme( new BatchEvmScheme(signer), new ExactEvmScheme(signer), ); client.register("eip155:*", composite); ``` See [Full buyer integration guide](/gateway-nanopayments/howtos/x402-buyer). ### Facilitator Use `isBatchPayment()` to route Gateway payments to `BatchFacilitatorClient` while your existing handler covers standard payments: ```ts theme={null} import { BatchFacilitatorClient, isBatchPayment, } from "@circle-fin/x402-batching/server"; const gatewayClient = new BatchFacilitatorClient(); async function handleSettle(payload, requirements) { if (isBatchPayment(requirements)) { return gatewayClient.settle(payload, requirements); } return existingOnChainHandler.settle(payload, requirements); } ``` See [Full facilitator integration guide](/gateway-nanopayments/howtos/facilitator-integration). ## How routing works When both payment methods are available, routing is automatic at every layer: | Layer | What happens | | - | - | | Server | The `402` response lists both standard and Gateway options in the `accepts` array. | | Client | `CompositeEvmScheme` checks each option's `extra.name`. If `"GatewayWalletBatched"` is present, it uses `BatchEvmScheme`. Otherwise it uses `ExactEvmScheme`. | | Facilitator | `isBatchPayment()` checks the same `extra.name` field and routes [verify](/api-reference/gateway-nanopayments/verify-x402payment)/[settle](/api-reference/gateway-nanopayments/settle-x402payment) calls to either Gateway or the existing onchain handler. | No manual routing code is needed in sellers or buyers. The SDK handles it based on the payment requirements.