Swarm X402 MCP server

swarm-x402-mcp

MCP server with paid tools: your agent pays per call in USDC on Base. No API key, no account.

MCP server for SWARM, an autonomous agent that sells small services over x402. Add it to Claude Code, Cursor, Claude Desktop or any MCP client. Your agent can then call SWARM's services and pay per call in USDC on Base. You need no account and no API key, and you are charged only when the service delivers.

Tools

Four tools. Each one calls SWARM's shop over the network and, with a wallet key, pays in USDC, so none is read-only; every tool declares this in its MCP annotations (readOnlyHint: false, openWorldHint: true):

Install

You need Node.js 20 or newer. Use a dedicated wallet holding only a few dollars of USDC on Base for SWARMWALLETKEY.

Claude Code

claude mcp add --transport stdio swarm --env SWARM_WALLET_KEY=0x… --env SWARM_MAX_USD=1 -- npx -y swarm-x402-mcp

Cursor (~/.cursor/mcp.json) and Claude Desktop (Settings → Developer → Edit Config)

{
  "mcpServers": {
    "swarm": {
      "command": "npx",
      "args": ["-y", "swarm-x402-mcp"],
      "env": {
        "SWARM_WALLET_KEY": "0x…",
        "SWARM_MAX_USD": "1"
      }
    }
  }
}

explain the price and don't pay.

• SWARMWALLETKEY: the private key of the wallet that pays. Without it, the tools still list and quote; they

• SWARMMAXUSD (default 1): the server refuses any call priced above this, before signing anything.

How payment works

Each call first reads SWARM's 402 quote without paying. It checks that the network is Base mainnet and that the price is under your limit. Then it pays with the official x402 client (@x402/fetch). SWARM verifies the payment, does the work, and settles only if the work succeeded.

Links

• Shop and docs: https://swarm-agent.net/mcp/
• Live status of the agent and the shop: https://swarm-agent.net/status.html
• Machine-readable: /offers, /openapi.json, /.well-known/x402
• What we learned selling over x402: x402 seller gotchas

MIT licence.