> ## 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. # Create FX trade > Creates a cross-currency trade ## OpenAPI ````yaml openapi/cross-currency.yaml post /v1/exchange/trades openapi: 3.0.2 info: version: ${version} title: Cross-Currency API description: > The Circle Cross-Currency API allows you to exchange fiat for USDC and exchange USDC for EURC. servers: - url: https://api-sandbox.circle.com - url: https://api.circle.com security: [] tags: - name: Trades description: Execute currency exchange trades. - name: Payments description: Payment endpoints. - name: Settlements description: Settlement endpoints paths: /v1/exchange/trades: post: tags: - Trades summary: Create FX trade description: Creates a cross-currency trade operationId: createFxTrade requestBody: content: application/json: schema: $ref: '#/components/schemas/FxTradeRequest' responses: '200': description: Successfully created trade. headers: X-Request-Id: $ref: '#/components/headers/XRequestId' content: application/json: schema: $ref: '#/components/schemas/CreateFxTradeResponse' examples: response: value: data: id: b8627ae8-732b-4d25-b947-1df8f4007a29 from: amount: '3.14' currency: USDC to: amount: '3.14' currency: USDC status: pending createDate: '2020-04-10T02:13:30.000Z' updateDate: '2020-04-10T02:13:30.000Z' quoteId: b8627ae8-732b-4d25-b947-1df8f4007a29 source: type: wallet id: '12345' destination: type: wallet id: '12345' clientEntityId: a3f1b2c4-d5e6-7890-abcd-ef1234567890 '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/NotAuthorized' '404': $ref: '#/components/responses/NotFound' security: - bearerAuth: [] components: schemas: FxTradeRequest: type: object required: - idempotencyKey - quoteId properties: idempotencyKey: $ref: '#/components/schemas/IdempotencyKey' quoteId: $ref: '#/components/schemas/Id' CreateFxTradeResponse: title: CreateFxTradeResponse properties: data: type: object properties: id: $ref: '#/components/schemas/Id' from: $ref: '#/components/schemas/FxMoney' to: $ref: '#/components/schemas/FxMoney' status: $ref: '#/components/schemas/TradeStatus' createDate: $ref: '#/components/schemas/UtcTimestamp' updateDate: $ref: '#/components/schemas/UtcTimestamp' quoteId: $ref: '#/components/schemas/Id' source: $ref: '#/components/schemas/FxLocation' destination: $ref: '#/components/schemas/FxLocation' clientEntityId: $ref: '#/components/schemas/ClientEntityId' IdempotencyKey: type: string description: >- Universally unique identifier (UUID v4) idempotency key. This key is utilized to ensure exactly-once execution of mutating requests. format: uuid example: ba943ff1-ca16-49b2-ba55-1057e70ca5c7 Id: type: string description: Unique system generated identifier for the entity. format: uuid example: b8627ae8-732b-4d25-b947-1df8f4007a29 FxMoney: type: object required: - amount - currency properties: amount: description: Magnitude of the amount, in units of the currency, with a `.`. type: string example: '3.14' currency: $ref: '#/components/schemas/FxCurrency' TradeStatus: type: string description: Status of the trade. enum: - pending - confirmed - failed - complete - pending_settlement UtcTimestamp: type: string description: ISO-8601 UTC date/time format. example: '2020-04-10T02:13:30.000Z' FxLocation: description: > A location representing either a wallet or a fiat rail account (`wire` or `pix`). type: object required: - type - id properties: type: type: string description: > The location type. Use `wallet` for a sub-account wallet. Use `wire` or `pix` for a registered fiat rail account. enum: - wallet - wire - pix example: wallet id: type: string description: > The account identifier. For `wallet` locations this is a numeric account number; for fiat rail locations this is the UUID of the registered fiat account. example: '12345' ClientEntityId: type: string format: uuid description: >- Identifier of the client entity (sub-account) associated with this resource. example: a3f1b2c4-d5e6-7890-abcd-ef1234567890 FxCurrency: type: string enum: - USDC - EURC - MXN - BRL headers: XRequestId: description: >- Universally unique identifier (UUID v4) for the request. Helpful for identifying a request when communicating with Circle support. schema: type: string format: uuid example: 2adba88e-9d63-44bc-b975-9b6ae3440dde responses: BadRequest: description: The request cannot be processed due to a client error. headers: X-Request-Id: $ref: '#/components/headers/XRequestId' content: application/json: schema: type: object title: BadRequest required: - code - message properties: code: type: integer example: 400 message: type: string example: Something went wrong. example: code: 400 message: Bad request. examples: response: value: code: 400 message: Bad request. NotAuthorized: description: >- The request has not been applied because it lacks valid authentication credentials. headers: X-Request-Id: $ref: '#/components/headers/XRequestId' content: application/json: schema: type: object title: NotAuthorized required: - code - message properties: code: type: integer example: 400 message: type: string example: Something went wrong. example: code: 401 message: Malformed authorization. examples: response: value: code: 401 message: Malformed authorization. NotFound: description: The specified resource was not found. headers: X-Request-Id: $ref: '#/components/headers/XRequestId' content: application/json: schema: type: object title: NotFound required: - code - message properties: code: type: integer example: 400 message: type: string example: Something went wrong. example: code: 404 message: Not found. examples: response: value: code: 404 message: Not found. securitySchemes: bearerAuth: type: http scheme: bearer ````