> ## 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 an attestation > Retrieves the signed attestation for a USDC burn event on the source chain. ## OpenAPI ````yaml openapi/cctp.yaml get /v1/attestations/{messageHash} openapi: 3.0.2 info: version: '1.0' title: Cross-Chain Transfer Protocol (CCTP) description: > Circle's Cross-Chain Transfer Protocol enables you to build seamless user experiences for sending and transacting USDC natively across blockchains. CCTP endpoints enable advanced capabilities such as fetching attestations for faster-than-finality burn events, verifying public keys across versions, accessing transaction details, querying Fast Transfer allowances and fees, and initiating re-attestation processes. servers: - url: https://iris-api-sandbox.circle.com - url: https://iris-api.circle.com security: [] tags: - name: CCTP description: Cross-Chain Transfer Protocol endpoints - name: CCTP V1 (Legacy) description: Legacy Cross-Chain Transfer Protocol endpoints - name: Quotes description: Signed, time-bound fee quotes for USDC transfers paths: /v1/attestations/{messageHash}: get: tags: - CCTP V1 (Legacy) summary: Get an attestation description: >- Retrieves the signed attestation for a USDC burn event on the source chain. operationId: getAttestation parameters: - $ref: '#/components/parameters/MessageHashPath' responses: '200': description: >- Successfully retrieved either the signed attestation or the message is still pending block confirmations. content: application/json: schema: $ref: '#/components/schemas/GetAttestationV1Response' examples: complete: value: attestation: >- 0xdc485fb2f9a8f68c871f4ca7386dee9086ff9d4387756990c9c4b9280338325252866861f9495dce3128cd524d525c44e8e7b731dedd3098a618dcc19c45be1e1c status: complete pending confirmations: value: attestation: null status: pending_confirmations '404': $ref: '#/components/responses/NotFound' components: parameters: MessageHashPath: name: messageHash description: > Message hash for the message being bridged. This can be generated using the `keccak256` hash of the message bytes emitted by the `MessageSent` event. in: path required: true schema: type: string pattern: ^0x[a-fA-F0-9]{64}$ example: '0x912f22a13e9ccb979b621500f6952b2afd6e75be7eadaed93fc2625fe11c52a2' schemas: GetAttestationV1Response: title: GetAttestationSuccessResponse type: object description: Signed or pending attestation. required: - status properties: attestation: type: string description: > Signed attestation corresponding to the given `messageHash` parameter. This is null if the event has been seen but the attestation is still pending block confirmations. example: >- 0x6edd90f4a0ad0212fd9fbbd5058a25aa8ee10ce77e4fc143567bbe73fb6e164f384a3e14d350c8a4fc50b781177297e03c16b304e8d7656391df0f59a75a271f1b nullable: true status: $ref: '#/components/schemas/AttestationStatus' AttestationStatus: type: string description: >- Status of the attestation, whether it is signed or awaiting more block confirmations. enum: - complete - pending_confirmations XRequestId: type: string format: uuid description: >- A unique identifier, which can be helpful for identifying a request when communicating with Circle support. example: 2adba88e-9d63-44bc-b975-9b6ae3440dde responses: NotFound: content: application/json: schema: type: object title: NotFoundResponse required: - code - message properties: code: type: integer description: Code that corresponds to the error. message: type: string description: Message that describes the error. example: code: 404 message: Not found. description: Specified resource was not found. headers: X-Request-Id: $ref: '#/components/headers/XRequestId' headers: XRequestId: description: > Developer-provided header parameter or Circle-generated universally unique identifier (UUID v4). Useful for identifying a specific request when communicating with Circle Support. schema: $ref: '#/components/schemas/XRequestId' ````