🍋 LemonCake — agent-payment-mcp

Let your AI agent pay for any API — capped, no account.

Give your agent a spend-capped prepaid wallet and it pays for paid APIs on its own. Discover → pay → pass through. No per-call key, no human in the loop, and it can't exceed your cap. First 3,000 calls free, then 3%. Seller gets 97%. LemonCake never holds your funds.

💰 No monthly fee. First 3,000 calls free (lifetime). Then 3% only when your API earns. See pricing →

⚡ 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, then ask:

"use lemon to translate 'Hello, agent payments' to Japanese"

Zero env vars. Zero signup. Zero credit card. Demo Mode activates automatically.

🎁 8 free demo tools (real APIs, no auth)

| Tool | What it does | Upstream | |---|---|---| | 🔍 demo_search | Search Wikipedia (5 results + URLs) | en.wikipedia.org | | 💱 demo_fx | Live FX rates (160+ currencies) | open.er-api.com | | 🌐 demo_translate | Translate 80+ languages | MyMemory | | 🌤 demo_weather | Current weather for any lat/lon | Open-Meteo | | 📍 demo_geocode | Place name → coordinates | OpenStreetMap Nominatim | | 🕐 demo_time | Current time + DST for any IANA timezone | worldtimeapi | | 📖 demo_dictionary | English definitions / synonyms | dictionaryapi.dev | | 🔁 demo_echo | HTTP echo (request inspector) | httpbin.org |

💳 How agents pay for APIs (x402 autonomous payment)

LemonCake speaks x402 — the HTTP 402 payment protocol for AI agents.

Agent → POST /g/<endpoint>
         ↓
  402 + accepts[] { pricePerCall, buyUrl, mintUrl }
         ↓
  Agent mints a Pay Token (off-session, capped wallet)
         ↓
  Bearer <jwt> → gateway → your API

1. Seller registers any HTTP API at lemoncake.xyz/app and sets a price per call
2. Buyer prepays via card → Pay Token (JWT) issued automatically
3. Agent passes Authorization: Bearer <token> — gateway verifies, meters, forwards
4. Budget exhausted → gateway returns 402 + accepts[] so agents can self-fund

🤖 Agent autonomous top-up (Agent Funding API)

For fully autonomous operation with no human per-session:

1. Issue a Buyer Key (bk_...) in the Pay Tokens pane at /app
2. Save a card once at /agent/fund
3. Agent uses bk_ to mint/top-up Pay Tokens off-session — hard-capped per your limits

Agent → POST /api/lc/agent/tokens (Bearer bk_...)
         → off-session card charge → Pay Token issued
         → Bearer <jwt> → gateway → pass through

Caps enforced server-side: per-mint / daily / monthly. Cannot overspend.

🏪 Publish your own API (for sellers)

Monetize any HTTP API or MCP server in minutes:

1. Sign in at lemoncake.xyz/app
2. Add API → paste your URL, set price per call
3. Share the buy link — buyers prepay with a card, Pay Token issued automatically
4. You keep 97%. LemonCake takes 3% once at checkout. Never holds funds (Stripe Connect Direct Charge).

// Your tool code is unchanged — LemonCake sits in front as a gateway
class MyTool extends MCPTool {
  // existing logic — no SDK required
}
// Route traffic through: https://lemoncake.xyz/g/<shortId>

🌍 Compliance — registration not required in 7 jurisdictions

Japan FSA Fintech Support Desk (2026-06) confirmed: no electronic payment means management registration required. LemonCake never holds funds (Stripe Connect Direct Charge, custody-free).

| Jurisdiction | Basis | |---|---| | 🇯🇵 Japan | FSA confirmed — registration not required | | 🇺🇸 USA | FinCEN 2019 §4.5 — non-custodial software ≠ MSB | | 🇪🇺 EU | MiCA — non-CASP | | 🇬🇧 UK | FCA — Tech Service Provider | | 🇸🇬 Singapore | MAS — DPT non-applicable | | 🇨🇦 Canada | FINTRAC — non-custodial exemption | | 🇨🇭 Switzerland | FINMA — non-financial intermediary |

Full posture: lemoncake.xyz/security

🔌 The LemonCake family

| Package | Use | |---|---| | agent-payment-mcp | Main MCP — x402 gateway + agent payment rail (this one) | | @lemon-cake/mcp-sdk | SDK to monetize your own MCP server | | xstocks-mcp | Buy tokenized US stocks on Solana | | alpaca-guard-mcp | Alpaca paper / live trading with hard USD cap | | tokenized-stock-mcp | Dinari dShares |

🛡 Security

• Server-side hard caps — per-mint / daily / monthly limits enforced on the server. Cannot be exceeded.
• Pay Token = JWT — signed HS256, verified on every gateway call. Not a blockchain asset.
• No private keys in the MCP server — Buyer Key (bk_) has hashed secret, PM reference only (no raw card data).
• Stripe Connect Direct Charge — funds go seller-direct. LemonCake never holds USDC or fiat.
• RLS on all DB tables, upstream_auth never returned in API responses.

Links

| | | |---|---| | Try demo | npx -y agent-payment-mcp or lemoncake.xyz/demo | | Seller dashboard | lemoncake.xyz/app | | Agent card setup | lemoncake.xyz/agent/fund | | Docs | lemoncake.xyz/docs | | Source | github.com/evidai/agent-payment-mcp | | MCP Registry | registry.modelcontextprotocol.io | | License | MIT |