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.

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.

Variable	Purpose
X402_NETWORK	CAIP-2 network. eip155:8453 (Base mainnet, default) or eip155:84532 (Sepolia).
X402_FACILITATOR_URL	Facilitator base URL, no /verify suffix. Defaults per network.
PAYGATE_WALLET_ADDRESS	Wallet that receives payments.
CONTACT_EMAIL	Optional; omitted from the UCP manifest when empty.
CDP_API_KEY_ID / CDP_API_KEY_SECRET	Coinbase CDP credentials. Required for mainnet — it is the only facilitator that settles on Base.
UPSTREAM_AUTH_TOKEN	Token forwarded to the developer's MCP server.
STRIPE_SECRET_KEY	Optional, for the Stripe path on tools priced ≥ $0.50.

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