> ## 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. # Get full TransferSpec by transferSpecHash > Retrieve the full TransferSpec for a given transferSpecHash. ## OpenAPI ````yaml openapi/gateway.yaml get /v1/transferSpec/{transferSpecHash} openapi: 3.0.3 info: title: Circle Gateway version: 1.0.0 description: > Circle Gateway allows you to create a chain-abstracted USDC balance and transfer it instantly to any supported destination chain. servers: - url: https://gateway-api-testnet.circle.com - url: https://gateway-api.circle.com security: [] tags: - name: Gateway description: >- Endpoints for getting a unified USDC balance and creating attestations for transfer - name: Gateway Batch description: Endpoints for batch processing of EIP-3009 authorizations - name: Webhook Subscriptions description: Manage webhook subscriptions for Gateway event notifications. paths: /v1/transferSpec/{transferSpecHash}: get: tags: - Gateway summary: Get full TransferSpec by transferSpecHash description: Retrieve the full TransferSpec for a given transferSpecHash. operationId: GetTransferSpec parameters: - name: transferSpecHash in: path required: true description: The keccak256 hash of the TransferSpec schema: $ref: '#/components/schemas/Bytes32' responses: '200': description: TransferSpec information content: application/json: schema: $ref: '#/components/schemas/TransferSpecResponse' '400': description: Invalid transferSpecHash format '404': description: TransferSpec not found '500': description: Internal server error components: schemas: Bytes32: type: string pattern: ^0x[a-fA-F0-9]{64}$ example: '0x1234567890123456789012345678901234567890123456789012345678901234' description: A 32-byte hex string. TransferSpecResponse: type: object description: Complete TransferSpec information properties: version: type: integer description: Version of the transfer spec (uint32). example: 1 sourceDomain: type: integer description: The domain of the wallet contract this transfer came from (uint32). example: 0 destinationDomain: type: integer description: >- The domain of the minter contract this transfer is valid for (uint32). example: 4 sourceContract: type: string description: >- The address of the wallet contract on the source domain (32-byte padded). example: '0x000000000000000000000000557777735b1dd18194f1b84256be2a3cdee6cb6f' destinationContract: type: string description: >- The address of the minter contract on the destination domain (32-byte padded). example: '0x000000000000000000000000552222279206cb0434128e0cae4558a25779c79f' sourceToken: type: string description: The token address on the source domain (32-byte padded). example: '0x0000000000000000000000001c7d4b196cb0c7b01d743fbc6116a902379c7238' destinationToken: type: string description: The token address on the destination domain (32-byte padded). example: '0x000000000000000000000000036cbd53842c5426634e7929541ec2318f3dcf7e' sourceDepositor: type: string description: >- The address to debit within the wallet contract on the source domain (32-byte padded). example: '0x0000000000000000000000002b45eF6A547A73eA248A1bCED808575c5a4839eE' destinationRecipient: type: string description: >- The address that should receive the funds on the destination domain (32-byte padded). example: 0x0000000000000000000000008BA1f109551bD432803012645Hac136c95e5431 sourceSigner: type: string description: The signer who signed for the transfer (32-byte padded). example: '0x000000000000000000000000742d35Cc6623C026c893b7c2FD85c4E4A0EF4321' destinationCaller: type: string description: >- The address of the caller who may use the attestation, 0 address if any caller (32-byte padded). example: '0x0000000000000000000000000000000000000000000000000000000000000000' value: type: string description: The amount to be transferred. example: '1000000' salt: type: string description: The salt value used in the transfer spec. example: '0x1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef' hookData: type: string description: Additional hook data for the transfer spec. example: 0x required: - version - sourceDomain - destinationDomain - sourceContract - destinationContract - sourceToken - destinationToken - sourceDepositor - destinationRecipient - sourceSigner - destinationCaller - value - salt - hookData ````