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Circle Agent Stack for AI agents: USDC wallets, spend policies, transfers, and x402 nanopayments.
About
Circle Agent Stack for AI agents: USDC wallets, spend policies, transfers, and x402 nanopayments.
Security Report
The circle-agent-stack-mcp server is well-designed with strong input validation, proper authentication via environment variables, and appropriate permission scoping. The codebase demonstrates defensive programming practices with comprehensive Zod schemas, no hardcoded secrets, and comprehensive test coverage. Minor code quality observations around error handling do not materially impact security. Supply chain analysis found 4 known vulnerabilities in dependencies (0 critical, 3 high severity). Package verification found 1 issue.
7 files analyzed · 10 issues found
Security scores are indicators to help you make informed decisions, not guarantees. Always review permissions before connecting any MCP server.
Permissions Required
This plugin requests these system permissions. Most are normal for its category.
What You'll Need
Set these up before or after installing:
Environment variable: CIRCLE_API_KEY
How to Install
Add this to your MCP configuration file:
{
"mcpServers": {
"io-github-kinance-circle-agent-stack-mcp": {
"env": {
"CIRCLE_API_KEY": "your-circle-api-key-here"
},
"args": [
"-y",
"circle-agent-stack-mcp"
],
"command": "npx"
}
}
}Documentation
View on GitHubFrom the project's GitHub README.
circle-agent-stack-mcp
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
| Tool | What it does |
|---|---|
circle_wallet_create | Create an agent wallet (dev/hosted/smart) |
circle_wallet_list | List wallets with USDC balances |
circle_balance | Balance + last 10 txns for a wallet |
circle_policy_set | Set daily cap, x402 cap, allow/block lists |
circle_transfer_usdc | Send USDC to an on-chain address |
circle_x402_pay | Pay an x402-priced endpoint and return its response |
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_usdcbefore enabling automated payments - Start on
type="dev"wallets, not mainnet - Review the
allowlistbefore 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
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