Paid MCP Metering

paid-mcp-metering

Metered MCP tools, priced per call.

Discovery is free: POST /mcp speaks JSON-RPC 2.0 per the Model Context Protocol (initialize, tools/list, ping). Execution is metered: POST /v1/t/{tool} sits behind an x402 v2 paywall. An unpaid request gets HTTP 402 with payment requirements; a paid request carries a PAYMENT-SIGNATURE header and settles USDC through the facilitator before the tool runs.

Live deployment

Base URL: https://paid-mcp-metering.vercel.app

• GET /health — free, public
• POST /mcp — free discovery
• POST /v1/t/{tool} — metered; currently answers 503 settlement_not_configured because X402_PAY_TO is unset on the deployment (settlementConfigured:false in /health is the honest switch). No payment can be accepted until a receiving address is configured.

server.json declares this URL as the registry remote.

Tools

Tool	Price	What it returns
web_search	$0.001/call	Ranked live web results with source URLs
deep_research	$0.01/call	Multi-source research pass with a synthesized answer plus cited sources

Upstreams are Exa (primary) and Tavily (fallback). Every handler returns live upstream output or throws — there is no canned response.

Rails

x402 v2, USDC, EIP-155 network selected by X402_NETWORK (default Base Sepolia testnet, CAIP-2 eip155:84532). Facilitator defaults to https://x402.org/facilitator.

Env var	Purpose
X402_PAY_TO	Receiving address. Required for settlement; unset serves 402 requirements only
X402_NETWORK	CAIP-2 network id (default eip155:84532)
X402_FACILITATOR_URL	x402 facilitator endpoint
EXA_API_KEY / TAVILY_API_KEY	Search upstream credentials

Run

npm install
npm run build
npm start          # node dist/x402-server.js
npm test           # build + node --test dist/test-x402.js

Free discovery:

curl -s localhost:4021/mcp -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

Paid execution:

curl -s localhost:4021/v1/t/web_search -H 'Content-Type: application/json' \
  -d '{"query":"x402 protocol","max_results":3}'
# -> 402 with payment requirements; pay via an x402 client and retry with PAYMENT-SIGNATURE

Registry

server.json targets the official MCP Registry as io.github.dev55acc-ai/paid-mcp-metering. Tagging v* runs .github/workflows/publish-mcp.yml: tests, build, npm publish (when NPM_TOKEN is set), then registry publish authenticated by GitHub OIDC — no stored registry credential.

License

MIT