> ## 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. # Modify an order > Changes the fee limit on a resting order. Only the fee changes; the order remains in `pending` status with its original size and side. Outside the lock window, the fee can move in either direction. During the lock window, the new value must be more competitive than the current value (lower for BURN orders, higher for MINT orders); a less competitive value returns error 137005. Setting `feeBps` to null converts the order to a market order. ## OpenAPI ````yaml openapi/match.yaml post /v1/match/orders/modify openapi: 3.1.0 info: title: Circle Match API description: > The Circle Match API provides endpoints for Circle Match, a periodic batch-auction venue that coordinates USDC burn demand with USDC mint demand for eligible Circle Mint customers. ## Authentication All REST endpoints require a Bearer token: ``` Authorization: Bearer ``` ## WebSocket Real-time auction state and account events are delivered over a persistent WebSocket connection at `wss://api.circle.com/v1/match/ws` (production) or `wss://api-sandbox.circle.com/v1/match/ws` (sandbox). Obtain a short-lived ticket with `POST /v1/match/ws/ticket`, then pass two `Sec-WebSocket-Protocol` values in the upgrade request: - `circle-match.v1` - `ticket.` — the ticket value, prefixed with `ticket.` After connection, subscribe to the `market` channel for public auction state or the `account` channel for private order and fill events. See the Circle Match WebSocket reference for the full protocol specification. ## Error codes | Code | HTTP | Description | |--------|------|-------------| | 136001 | 400 | Auction locked — cancellations and less-competitive fee changes not accepted | | 136002 | 400 | Auction settling — try again after settlement completes | | 137001 | 400 | Insufficient available balance | | 137002 | 400 | Invalid wallet | | 137003 | 400 | Wallet not found | | 137004 | 409 | Idempotency key reused with different parameters | | 137005 | 400 | Fee change not more competitive during lock window | | 137006 | 409 | Self-match violation — open order on opposite side of same auction | | 137007 | 400 | Invalid fiat account | | 137008 | 400 | Maximum orders per auction reached | | 137009 | 400 | Transaction limit exceeded | | 137010 | 400 | Entity not eligible for Circle Match | | 138001 | 400 | Withdrawal amount exceeds available balance | | 138002 | 400 | Withdrawal request invalid | | 138003 | 404 | No Circle Match account found for this entity | | 138004 | 400 | Invalid withdrawal destination | | 139001 | 400 | Circle Match wallet invalid | version: 1.0.0 servers: - url: https://api.circle.com description: Production - url: https://api-sandbox.circle.com description: Sandbox security: - BearerAuth: [] tags: - name: Account description: Account balance and activity summary - name: Orders description: Place, list, retrieve, cancel, and modify orders - name: Withdrawals description: Withdraw restricted mint-side USDC - name: WebSocket description: Obtain a WebSocket connection ticket paths: /v1/match/orders/modify: post: tags: - Orders summary: Modify an order description: >- Changes the fee limit on a resting order. Only the fee changes; the order remains in `pending` status with its original size and side. Outside the lock window, the fee can move in either direction. During the lock window, the new value must be more competitive than the current value (lower for BURN orders, higher for MINT orders); a less competitive value returns error 137005. Setting `feeBps` to null converts the order to a market order. operationId: modifyOrder requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/ModifyOrderRequest' example: auctionId: 42 orderId: 550e8400-e29b-41d4-a716-446655440000 feeBps: '3' responses: '200': description: Order modified content: application/json: schema: type: object required: - data properties: data: type: object required: - auctionId - orderId - status properties: auctionId: type: integer example: 42 orderId: type: string format: uuid example: 550e8400-e29b-41d4-a716-446655440000 status: type: string enum: - pending example: pending '400': description: >- Bad request. Error code: `137005` — during the lock window the new fee is less competitive than the current fee. content: application/json: schema: $ref: '#/components/schemas/Error' '401': description: Unauthorized content: application/json: schema: $ref: '#/components/schemas/Error' components: schemas: ModifyOrderRequest: type: object required: - auctionId - orderId properties: auctionId: type: integer description: Auction cycle that contains the order to modify example: 42 orderId: type: string format: uuid description: UUID of the order to modify example: 550e8400-e29b-41d4-a716-446655440000 feeBps: oneOf: - type: string - type: 'null' description: >- New fee limit in basis points. During the lock window the new value must be more competitive than the current value (lower for BURN, higher for MINT). Set to null to convert the order to a market order. example: '3' Error: type: object required: - code - message properties: code: type: integer description: Circle error code example: 137001 message: type: string description: Human-readable error description example: Insufficient available balance securitySchemes: BearerAuth: type: http scheme: bearer ````