---

⚡ Try in 30 seconds — no signup

Add to ~/Library/Application Support/Claude/claude_desktop_config.json (or Cursor / Cline):

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

Restart Claude Desktop, then ask:

"use lemon to search Wikipedia for AI agents"

Demo Mode runs against real Wikipedia, real FX rates, and real httpbin APIs. No credentials needed.

---

💳 Unlock paid services

To use Serper (Google search), Hunter.io, gBizINFO, and more:

1. Open lemoncake.xyz/start/v2
2. Sign in with Google (Privy creates an embedded wallet — keys stay on your device)
3. Get USDC via Apple Pay / Coinbase / JPY bank transfer (built in)
4. Sign one ERC-2612 permit — "up to $25/day, valid 90 days". One click. No gas.
5. Copy the LEMON_CAKE_PERMIT blob into your MCP config:

{
  "mcpServers": {
    "lemon": {
      "command": "npx",
      "args": ["-y", "agent-payment-mcp"],
      "env": {
        "LEMON_CAKE_PERMIT": "<paste the permit blob here>"
      }
    }
  }
}

After that, every API call settles directly from your wallet to the API provider with no signing prompts for 90 days. LemonCake never holds your USDC.

---

What is LemonCake?

LLM agents are getting powerful — but they still can't pay for things autonomously.

LemonCake solves this with ERC-2612 permits: a single 90-day signature that lets an AI agent spend up to a daily cap from your wallet, directly to API providers. The agent calls paid APIs through our MCP server, gets charged per call in USDC, and stops automatically when the daily cap is reached.

You                    Agent                  Paid API
 │                       │                        │
 ├─ sign one permit ──▶  │                        │
 │   $25/day, 90 days    │                        │
 │                       ├─ call_service ───────▶ │
 │                       │   uses LEMON_CAKE_PERMIT
 │                       │                        │
 │                       │  ◀─ response + receipt ┤
 │                       │     on-chain transferFrom

Budget exhausted? Hard stop until tomorrow. Permit expired? Re-sign in one click. No runaway agents, no stolen API keys, no platform middleman holding your USDC.

---

🔌 Family of MCP packages

Package	What it does
agent-payment-mcp	Main entry — pay-per-call any HTTP API in the LemonCake marketplace
xstocks-mcp	Buy tokenized US stocks (AAPLx, TSLAx, …) on Solana with USDC
alpaca-guard-mcp	Alpaca paper / live trading with hard daily USD cap
tokenized-stock-mcp	Buy Dinari dShares with USDC
polymarket-guard-mcp	Polymarket prediction markets with USDC
@lemon-cake/mcp-sdk	SDK for sellers to monetize their own MCP servers

---

🏗 Publish your API on LemonCake

Want to monetize your MCP server? Self-service registration at lemoncake.xyz/sellers:

• Enter your name, email, and Base wallet address
• Get a serviceId instantly
• Set your price per call (min $0.001)
• First 1,000 calls / month are free — Pattern 4 metering
• Above the free tier: $0.005/call default (you choose)
• USDC settles directly to your wallet — no platform middleman

Add billing in 3 lines:

import { withPayment } from "@lemon-cake/mcp-sdk";

server.tool("my_premium_tool", withPayment({ price: 0.01 }, async (args) => {
  return { content: [{ type: "text", text: "result" }] };
}));

---

✨ Features

For developers (buyers)

• ✅ Non-custodial — your USDC never leaves your wallet
• ✅ One signature — 90 days, hard daily cap, no gas
• ✅ Demo Mode — try without signup or credentials
• ✅ Apple Pay / Coinbase / JPY onramp built into /start/v2
• ✅ No JWT issuance, no API key juggling — drop the permit blob in, done

For API providers (sellers)

• ✅ Self-service registration at /sellers — no sales call
• ✅ USDC settles directly to your wallet — chargeback-impossible
• ✅ Free tier: 1,000 calls/month free per buyer (acquisition incentive)
• ✅ Stripe 60× cheaper — $0.005/call vs. $0.30+ Stripe minimum
• ✅ Global: no clearing-bank or KYC friction; works in any country

Infrastructure

• 🔧 Built on Base (USDC native, ~2-second blocks, $0.0001 gas)
• 🔧 Open-source MCP server (MIT license)
• 🔧 Audited (May 2026) — see security advisories
• 🔧 JP FSA registration not required — confirmed Q11 (2026-05-21)

---

🏗 Architecture

        ┌─────────────────────────────────────────────┐
        │  User wallet (Privy embedded / MetaMask)    │
        │                                             │
        │  ERC-2612 permit signature                  │
        │   ↳ spender = LemonCake marketplace addr    │
        │   ↳ value   = $25/day daily cap             │
        │   ↳ deadline= 90 days from now              │
        └────────────────────┬────────────────────────┘
                             │
                  LEMON_CAKE_PERMIT (one-time copy)
                             │
                             ▼
       ┌──────────────────────────────────────────────┐
       │  Claude / Cursor / Cline                     │
       │   ↳ MCP client                               │
       └────────────────────┬─────────────────────────┘
                             │  stdio
                             ▼
       ┌──────────────────────────────────────────────┐
       │  agent-payment-mcp (this repo)               │
       │   ↳ list_services()                          │
       │   ↳ call_service(serviceId, …)               │
       └────────────────────┬─────────────────────────┘
                             │  HTTPS
                             ▼
       ┌──────────────────────────────────────────────┐
       │  LemonCake charge API (Hono on Railway)      │
       │   ↳ POST /api/charges/permit                 │
       │   ↳ metering: 1000 free + $0.005/call paid   │
       └────────────────────┬─────────────────────────┘
                             │  permit() + transferFrom()
                             ▼
       ┌──────────────────────────────────────────────┐
       │  USDC contract on Base                       │
       │   ↳ user wallet ──→ provider wallet (direct) │
       └──────────────────────────────────────────────┘

LemonCake is the dotted middle box. It never holds USDC — every payment is a direct on-chain transferFrom(userWallet, providerWallet, amount).

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🌍 Why this is registration-exempt

The 2026-05-21 reply from Japan's FSA Fintech Support Desk (Q11) confirmed that a pure SDK distribution model where:

• LemonCake never touches user USDC
• LemonCake never operates the smart contract
• All payments settle directly user wallet → provider wallet

…does NOT require the "electronic payment means management" registration.

The same architecture is registration-exempt under 🇺🇸 FinCEN (2019 guidance §4.5), 🇪🇺 MiCA (non-CASP), 🇬🇧 FCA (Tech Service Provider), 🇸🇬 MAS (DPT non-applicable), 🇨🇦 FINTRAC, and 🇨🇭 FINMA. See lemoncake.xyz/security.

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🛡 Security

• On-chain hard cap — the daily cap is baked into the permit signature and enforced by the USDC contract itself. The MCP server cannot exceed it.
• No private keys in the MCP server — the permit blob is mathematically scope-limited.
• Auto-revoke on expiry — permits self-destruct after 90 days.
• Idempotency keys required on paid calls (no double-charges on retries).
• Audited May 2026 by @kleosr.

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📄 License

MIT.