> ## 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 fee for a trade > Returns the fee associated with the trade ID provided in the path parameter. ## OpenAPI ````yaml openapi/stablefx.yaml get /v1/exchange/stablefx/fees/{tradeId} openapi: 3.1.0 info: title: StableFX API description: > The StableFX API provides endpoints for trading stablecoins. ## Authentication All API requests require authentication using an API key. ## Base URL The base URL for all API endpoints is: `https://api.circle.com/v1/exchange/stablefx` version: 1.0.0 servers: - url: https://api.circle.com description: StableFX API server security: - BearerAuth: [] tags: - name: Quotes description: Endpoints for creating and managing quotes - name: Trades description: Endpoints for creating and managing trades - name: Signatures description: Endpoints for retrieving presign typed data and registering signatures - name: Fees description: Endpoints for retrieving fees - name: Funding description: Endpoints for funding trades - name: Webhook Subscriptions description: Manage subscriptions to notifications - name: Settlement Advance description: Request, track, and repay settlement advances. paths: /v1/exchange/stablefx/fees/{tradeId}: get: tags: - Fees summary: Get fee for a trade description: >- Returns the fee associated with the trade ID provided in the path parameter. operationId: getTradeFee parameters: - in: path name: tradeId required: true description: The ID of the trade. schema: $ref: '#/components/schemas/Id' responses: '200': description: Fee retrieved successfully content: application/json: schema: $ref: '#/components/schemas/Fee' security: - BearerAuth: [] components: schemas: Id: type: string format: uuid description: System-generated unique identifier of the resource. example: c4d1da72-111e-4d52-bdbf-2e74a2d803d5 Fee: type: object description: The fee details for a trade properties: tradeId: $ref: '#/components/schemas/Id' fee: $ref: '#/components/schemas/CurrencyAmount' CurrencyAmount: type: object description: Currency and amount details for a foreign exchange transaction required: - currency properties: currency: $ref: '#/components/schemas/Currency' amount: $ref: '#/components/schemas/Amount' Currency: type: string description: Currency code enum: - USDC - EURC Amount: type: string pattern: ^\d+(?:\.\d{1,6})?$ description: Amount of currency, formatted as a string with up to six decimal places. example: '100.00' securitySchemes: BearerAuth: type: http scheme: bearer bearerFormat: PREFIX:ID:SECRET description: >- Circle's API Keys are formatted in the following structure "PREFIX:ID:SECRET". All three parts are requred to make a successful request. ````