🍋 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)

💳 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).

Full posture: lemoncake.xyz/security

🔌 The LemonCake family

🛡 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.

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