PayGate MCP

Monetization gateway for Model Context Protocol servers. Put any MCP server behind a pay-per-call toll that AI agents can settle autonomously — no signup, no API keys, no human in the loop.

Live endpoint: https://paygate-mcp.rendercriativo.workers.dev/mcp

What it does

An agent calls a tool. If the tool is monetized, PayGate answers with an x402 v2 payment challenge instead of the result. The agent signs a USDC transfer authorization, retries, and gets its answer. Settlement happens on Base; the developer never touches payment code.

agent ──tools/call──▶ PayGate ──▶ 402 challenge (price, asset, payTo)
agent ──signed payload──▶ PayGate ──verify──▶ facilitator
                          PayGate ──▶ developer's MCP server ──▶ result
                          PayGate ──settle──▶ facilitator ──▶ USDC on Base
agent ◀── result + settlement receipt

Payment is verified before the tool runs and settled after it returns. If the tool fails or returns an error, nothing is charged.

Related MCP server: payclaw

For agents

Discovery is free. Ask PayGate what is for sale:

curl -X POST https://paygate-mcp.rendercriativo.workers.dev/mcp \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call",
       "params":{"name":"list_registered_servers","arguments":{}}}'

Calling a monetized tool without payment returns a spec-compliant challenge — a tool result with isError: true whose structuredContent holds the PaymentRequired object:

{
  "x402Version": 2,
  "error": "Payment required: calculate_fator_r custa $0.02 USDC.",
  "resource": { "url": "mcp://tool/calculate_fator_r", "mimeType": "application/json" },
  "accepts": [{
    "scheme": "exact",
    "network": "eip155:8453",
    "amount": "20000",                                     // 6-decimal USDC units
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "payTo": "0x82e3...999e",
    "maxTimeoutSeconds": 120,
    "extra": { "name": "USD Coin", "version": "2" }        // EIP-712 domain
  }]
}

Sign an EIP-3009 TransferWithAuthorization using exactly the domain in extra, then retry the call with the payment attached under params._meta["x402/payment"]. The settlement receipt comes back in _meta["x402/payment-response"].

The USDC EIP-712 domain name is "USD Coin" on Base mainnet and "USDC" on Base Sepolia. Using the wrong one makes every signature fail verification.

A working reference client is in scripts/pay-test.mjs:

PRIVATE_KEY=0x... node scripts/pay-test.mjs

The paying wallet needs USDC on Base — but no ETH: gas is covered by the facilitator.

Both x402 transports are supported. HTTP clients can use the base64 PAYMENT-REQUIRED / PAYMENT-SIGNATURE / PAYMENT-RESPONSE headers instead of the MCP _meta binding.

For developers who want to get paid

Register your existing MCP server and PayGate proxies it, charging per call:

curl -X POST https://paygate-mcp.rendercriativo.workers.dev/api/register \
  -H 'Content-Type: application/json' \
  -d '{"name":"Your Service",
       "target_server_url":"https://your-mcp-server.example.com/mcp",
       "wallet_address":"0xYourWallet"}'

You get back an API key and a proxy URL at /mcp/<devId>. Set per-tool prices via PUT /api/me/tools, check earnings at GET /api/me/earnings. Your server stays unchanged — PayGate forwards initialize, tools/list, resources/list and prompts/list for free, and charges only on tools/call.

Health and diagnostics

GET /health/x402 reports whether the payment rail is actually able to charge:

{
  "network": "eip155:8453",
  "facilitator": { "url": "...", "reachable": true, "authenticated": true },
  "ready_to_charge": true,
  "diagnosis": "Pronto para cobrar."
}

Configuration

Runtime values live in wrangler.jsonc (vars) and Cloudflare secrets.

Base Sepolia needs no credentials: the public facilitator at https://x402.org/facilitator settles testnet USDC for free — the cheapest way to try the whole flow.

Layout

src/
├── index.ts                 routes, health, discovery documents
├── x402/
│   ├── config.ts            network registry (CAIP-2, USDC assets, EIP-712 domains)
│   ├── protocol.ts          v2 structures, MCP + HTTP transport bindings
│   └── facilitator.ts       /verify and /settle, CDP JWT auth (EdDSA and ES256)
├── api/
│   ├── proxy.ts             the paid path: challenge → verify → execute → settle
│   ├── mcp-server.ts        PayGate's own MCP server (catalogue)
│   ├── register.ts          developer onboarding
│   ├── dev-management.ts    profile, pricing, earnings
│   └── discovery.ts         server card and UCP manifest
└── db/schema.ts             developers, tools, transactions, payment proofs

Development

npm install
npx wrangler dev      # local
npx wrangler deploy   # production

Built on Cloudflare Workers, Hono, and D1.

License

MIT