flowchart LR
  CL["Standard MCP client<br/>Claude Code, Inspector"] -->|stdio JSON-RPC| PX["Paying proxy<br/>holds the wallet, spend cap"]
  PX -->|Streamable HTTP + x402| SV["Paid MCP server<br/>gate in front of the handler"]
  SV -->|verify then settle| F[Facilitator]
  F -->|USDC| CA[(Catena sandbox account)]

  classDef pay stroke-width:2px
  class PX,SV pay

corepack enable
pnpm install
cp .env.example .env
# SELLER_PAY_TO_ADDRESS: your Catena sandbox account's base-sepolia USDC
#   deposit address, from app.catena.com
# BUYER_EVM_PRIVATE_KEY: a testnet wallet the proxy pays from. Fund it with
#   Base Sepolia USDC at https://faucet.circle.com (select Base Sepolia).
#   USDC only; no ETH is needed, transfers are gasless EIP-3009.

pnpm demo

curl -s http://localhost:4040/healthz

{"status":"ok","paidTool":"premium_market_signal","price":"$0.001"}

curl -si -X POST http://localhost:4040/mcp \
  -H 'content-type: application/json' \
  -H 'accept: application/json, text/event-stream' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"premium_market_signal","arguments":{"topic":"usdc"}}}' \
  | grep -i '^payment-required:' | tr -d '\r' | cut -d' ' -f2 | base64 -d

{"x402Version":2,"error":"Payment required","resource":{"url":"http://localhost:4040/mcp","description":"One invocation of the premium_market_signal MCP tool","mimeType":""},"accepts":[{"scheme":"exact","network":"eip155:84532","amount":"1000","asset":"0x036CbD53842c5426634e7929541eC2318f3dCF7e","payTo":"0x000000000000000000000000000000000000dEaD","maxTimeoutSeconds":300,"extra":{"name":"USDC","version":"2"}}]}

{
  "mcpServers": {
    "paid-market-signal": {
      "command": "pnpm",
      "args": ["--dir", "/path/to/x402-mcp-demo", "proxy"]
    }
  }
}