agent-payment-mcp — AI Agent Payment MCP Server

Give your AI agent a wallet. Pay-per-call USDC micropayments for any HTTP API — directly from Claude Desktop, Cursor, Cline, or any MCP client. No human approval per call. Kill switch included.

Try in 30 seconds (Demo Mode — no signup)

{
  "mcpServers": {
    "pay-per-call": {
      "command": "npx",
      "args": ["-y", "agent-payment-mcp"]
    }
  }
}

Leave LEMON_CAKE_BUYER_JWT unset → Demo Mode activates automatically. Calls hit real Wikipedia, httpbin, and live FX rate APIs with no charges.

💡 Or click "Try in Browser" on Glama → leave both env fields empty → click Start Inspector.

What it does

agent-payment-mcp lets an AI agent discover, pay for, and call premium HTTP APIs using USDC — with no human approval per call.

Agent (Claude / Cursor / Cline)
  │
  ├─ list_services()          → browse LemonCake API marketplace
  ├─ call_service(serviceId)  → invoke paid API, USDC deducted automatically
  ├─ check_balance()          → current USDC balance + spend limits
  ├─ setup()                  → onboarding guide if credentials missing
  ├─ check_tax(regNum)        → 国税庁 invoice number validation (Japan)
  └─ get_service_stats()      → usage + revenue analytics

Safety mechanisms

• Kill switch — halts all charges instantly (atomic, one-call revocation)

• Spend caps — session/daily USD ceiling the agent cannot exceed

• Pay Token (JWT) — scoped, short-lived spend credential; no raw wallet key exposed to the agent

• Idempotency — idempotencyKey parameter makes retries safe; no double-charges

Live mode (real USDC)

1. Sign up at lemoncake.xyz

2. Top up with USDC (min $5) or JPYC

3. Copy your Buyer JWT from the dashboard

{
  "mcpServers": {
    "pay-per-call": {
      "command": "npx",
      "args": ["-y", "agent-payment-mcp"],
      "env": {
        "LEMON_CAKE_BUYER_JWT": "eyJhbGci..."
      }
    }
  }
}

Tools reference

setup

Returns onboarding instructions if credentials are missing.

Input: none
Output:

{ "status": "ok", "mode": "demo", "message": "Set LEMON_CAKE_BUYER_JWT to enable live payments." }

list_services

Browse the LemonCake API marketplace.

Input: { "limit": 20 }

Output:

{
  "services": [
    { "id": "serper", "name": "Serper — Google Search", "priceUsdc": "0.005" }
  ]
}

call_service

Invoke a paid API. USDC is deducted from your balance automatically.

Input:

{
  "serviceId": "serper",
  "path": "/search",
  "method": "POST",
  "body": { "q": "AI agent payments" },
  "idempotencyKey": "req-abc-001"
}

Output (success):

{
  "status": 200,
  "chargeId": "ch_abc123",
  "amountUsdc": "0.005",
  "response": { "organic": ["..."] },
  "x402Receipt": {
    "scheme": "lemoncake-pay-token-v1",
    "x402Compatible": true,
    "amount": "0.005",
    "asset": "USDC",
    "settledAt": "2026-05-09T14:50:11.019Z"
  }
}

Output (budget exceeded):

{ "error": "BUDGET_EXCEEDED", "remaining": "0.00", "limit": "5.00" }

check_balance

Returns current USDC balance and KYA tier limits.

Output:

{
  "balanceUsdc": "4.995",
  "kyaTier": "standard",
  "dailyLimitUsdc": "50.00",
  "sessionSpentUsdc": "0.005"
}

check_tax

Validates a Japanese qualified-invoice (適格請求書) registration number against the 国税庁 API.

Input: { "registrationNumber": "T1234567890123", "amountJpy": 10000 }

Output:

{ "valid": true, "businessName": "株式会社Example", "registrationDate": "2023-10-01" }

get_service_stats

Returns aggregated usage data for all services.

Output:

{
  "totalCalls": 142,
  "totalSpentUsdc": "0.71",
  "byService": [{ "serviceId": "serper", "calls": 80, "spentUsdc": "0.40" }]
}

Available services

Full marketplace: lemoncake.xyz/services

x402 compatibility (since v0.5.1)

This server speaks the x402 protocol. Agent code written for on-chain x402 works unmodified:

• call_service returns x402Receipt on every successful charge

• Upstream 402 challenges are parsed (WWW-Authenticate, X-402-* headers, body x402 field)

• PAYMENT_PENDING semantics with retryAfterMs + idempotencyKey for async settlement

Environment variables

Leave both JWT vars unset → Demo Mode (no charges, real demo APIs).

Tested MCP clients

For MCP server developers

Add pay-per-call billing to your own MCP server in 3 lines:

npm install @lemon-cake/mcp-sdk

import { createLemonCakeSDK } from "@lemon-cake/mcp-sdk";
const lc = createLemonCakeSDK({ sellerKey: process.env.LEMONCAKE_SELLER_KEY });

execute: lc.charge({ price: 0.05 })(async (args) => myHandler(args))

Demo Mode activates automatically when LEMONCAKE_SELLER_KEY is absent.

Sibling MCPs

Local development

git clone https://github.com/evidai/agent-payment-mcp.git
cd agent-payment-mcp/mcp-server
npm install && npm run build && npm start

License

MIT © LemonCake · contact@aievid.com