> ## 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. # Crosschain transfers > Move digital assets across blockchains with native burn-and-mint, permissionless lock-and-mint, and unified balances. **Use dedicated SDKs for crosschain transfers** [Bridge Kit](https://www.npmjs.com/package/@circle-fin/bridge-kit) and [Unified Balance Kit](https://www.npmjs.com/package/@circle-fin/unified-balance-kit) let you move USDC across blockchains without low-level protocol work. Both support multiple blockchains and wallet providers. ## What you can build Move digital assets across blockchains with tools designed for speed, capital efficiency, and composability: * **Protocol-level integration**: Build with [CCTP](/cctp), Circle's permissionless protocol that natively transfers USDC and EURC using burn-and-mint, and supports permissionless wrapping of third-party assets using lock-and-mint. * **Chain-free UX**: A single [Gateway](/gateway) balance that works seamlessly across chains, enabling instant access to liquidity and a simplified experience for users. * **Agentic commerce**: Use [Gateway Nanopayments](/gateway-nanopayments) to enable gas-free USDC payments down to \$0.000001, purpose-built for AI agents, usage-based billing, and high-frequency sub-cent transactions. ## Choose your approach Each product is designed for different crosschain use cases. Pick the approach that matches your application needs. Permissionless burn-and-mint for USDC and EURC, and permissionless wrapping of third-party assets, with fast and standard options. Unified USDC balance instantly accessible across supported chains. No manual bridging required. ## When to use each product Understanding which tool fits your use case helps you build the right crosschain experience: CCTP is best when you need fine-grained control over crosschain transfers or want to build custom composable flows. It's a permissionless protocol that natively transfers USDC and EURC through burn-and-mint, and supports permissionless wrapping of third-party assets through lock-and-mint. Use CCTP when you need to integrate crosschain transfers at the smart contract level, require Fast Transfer for speed-sensitive use cases, or want to trigger automated actions post-transfer using Hooks. Gateway is designed for applications where users need instant access to their USDC across multiple chains without manual bridging. It's perfect for multichain apps, DEXs with chain abstraction, or any platform where users should see and spend one unified balance regardless of which chain they're on. Gateway eliminates the need for liquidity management across chains. Gateway Nanopayments extends Gateway with batched settlement to enable gas-free USDC payments at sub-cent scale. Use it when your application involves AI agents paying for resources, per-request billing, machine-to-machine commerce, or any scenario where per-transaction gas costs would exceed the payment value. ## Dive deeper * Explore the [CCTP technical guide](/cctp/technical-guide) to understand Fast Transfer and Standard Transfer options. * Read the Gateway quickstarts ([EVM](/gateway/quickstarts/unified-balance-evm), [Solana](/gateway/quickstarts/unified-balance-solana)) to create and use a unified USDC balance. * Explore [Gateway Nanopayments](/gateway-nanopayments) to build agentic commerce with gas-free, sub-cent USDC payments. * Learn about [CCTP supported blockchains](/cctp/cctp-supported-blockchains) and [Gateway supported blockchains](/gateway/references/supported-blockchains).