Circle Agent Stack MCP is an MCP server for interfacing with Circle's Agent Stack. It encapsulates wallet management, USDC transfers, and x402 nanopayments as capabilities executable via tool calls, described in the material as "create a wallet, set spending policies, send USDC, and pay x402-priced endpoints—all from one tool call."
Purpose and main capabilities:
- Wallet management: Create a USDC wallet and set spending policies.
- Transfers: Send USDC.
- Payments: Pay x402-priced endpoints.
- Self-hosted paywall: http-server.ts wraps the same set of tools behind an x402 paywall, and agents call them by paying per use in USDC instead of using an API key; this is suitable for exposing Circle tools as a paid service.
- Local testing: The x402 flow can be tested using the toy demo server in examples/x402-demo-server.mjs.
Usage:
- The Circle CLI must first be installed and authenticated.
- v0.1 performs all operations by calling the Circle CLI, in order to keep authentication handling out of this repository and avoid rewriting the API client before the tool interface is validated.
Security considerations (explicitly given in the material):
- Circle API keys have spending authority, so be sure to set daily_cap_usdc before enabling automatic payments.
- Start with a type="dev" wallet, not mainnet.
- Review the allowlist before going to production.
- Do not commit CIRCLE_API_KEY.
Roadmap (listed in the material):
- circle_nanopayment_stream: for per-token billing streaming x402 payments.
- circle_skills_list / circle_skills_call: Circle Skills marketplace.
- Direct HTTP API mode (v0.2): remove the CLI dependency.
- Multi-chain: EURC, CCTP cross-chain transfers.
Limitations: v0.1 depends on the Circle CLI; v0.2 is planned to switch to direct HTTP via @circle-fin/circle-sdk. The material does not provide specific fees, pricing, supported platforms, and actual usage effect descriptions.
