Circle Agent Stack

MCP server for Circle's Agent Stack. Create wallets, set spend policies, send USDC, and pay x402-priced endpoints — all from a tool call.

npx circle-agent-stack-mcp

Tools

Quickstart

You need the Circle CLI installed and authenticated:

npm install -g @circle-fin/circle-cli
circle login
export CIRCLE_API_KEY=your_key_here

Claude Desktop

{
  "mcpServers": {
    "circle": {
      "command": "npx",
      "args": ["-y", "circle-agent-stack-mcp"],
      "env": {
        "CIRCLE_API_KEY": "your_key_here"
      }
    }
  }
}

Claude Code

claude mcp add circle -- npx -y circle-agent-stack-mcp

Example

You: Create a dev wallet called eva-treasury, set a $5 daily cap and $0.10 x402 cap,
     then fetch today's BTC signal from the x402 endpoint at https://signals.example.co/btc

Claude:
→ circle_wallet_create("eva-treasury", type="dev")
  { wallet_id: "wal_abc123", address: "0x..." }

→ circle_policy_set("wal_abc123", daily_cap_usdc=5, x402_cap_usdc=0.10)
  { status: "applied" }

→ circle_x402_pay("wal_abc123", "https://signals.example.co/btc", max_price_usdc=0.10)
  { signal: "LONG", confidence: 0.72, price_paid_usdc: 0.05 }

Today's BTC signal: LONG (72% confidence). Paid $0.05.

Self-hosting with x402 paywall

http-server.ts wraps the same tools behind an x402 paywall — agents pay per call in USDC rather than using an API key. Useful if you want to expose Circle tooling as a paid service.

CIRCLE_PAYOUT_ADDRESS=0x... npm run start:http

To test the x402 flow locally, run the toy demo server in examples/x402-demo-server.mjs.

How it works

v0.1 shells out to the Circle CLI for all operations. This keeps auth handling out of this repo and avoids reimplementing the API client before the tool surface is validated. v0.2 will switch to direct HTTP via @circle-fin/circle-sdk.

Security

Your Circle API key has spend authority. Always:

• Set daily_cap_usdc before enabling automated payments
• Start on type="dev" wallets, not mainnet
• Review the allowlist before moving to production
• Don't commit CIRCLE_API_KEY

Roadmap

• circle_nanopayment_stream — streaming x402 payments for per-token billing
• circle_skills_list / circle_skills_call — Circle Skills marketplace
• Direct HTTP API mode (v0.2) — remove CLI dependency
• Multi-chain — EURC, CCTP cross-chain transfers

Related

• Circle Agent Stack docs
• x402 protocol
• Model Context Protocol