🍋 LemonCake

The billing, budget & identity layer for software for agents. Private Beta · Open core

Monetize any MCP/API in minutes, and let AI agents pay for it safely — each agent gets a spend-capped identity (budget, usage, pause/revoke). Buyers pay by card; no crypto wallet. First 3,000 calls free (lifetime). Then 3% only when your API earns.

![License: MIT (SDK)-green.svg)](LICENSE) ![Open core](#-open-core) ![MCP Compatible](https://modelcontextprotocol.io) ![x402 native](https://x402.org) ![npm: agent-payment-mcp](https://www.npmjs.com/package/agent-payment-mcp) ![FSA-confirmed](https://lemoncake.xyz/security) ![Glama score](https://glama.ai/mcp/servers/evidai/lemon-cake)

🚀 Get started · 💲 Pricing · 📚 Docs · 🌐 Live

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<sub>☝️ A real AI agent buys API calls by itself ($0.01 each), stops at its cap, and the API owner earns — no human, no crypto. · <a href="https://github.com/evidai/agent-unleashed">demo source</a></sub>

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🚀 Get started

Monetizing an MCP/API? Start here — one command:

npx create-lemon-mcp my-paid-mcp     # a paid MCP server, running in sandbox now
# then add a Seller Key in /app and set LEMONCAKE_SELLER_KEY → it charges for real (no code change)

Pick your path:

| I want to… | Do this | |---|---| | Monetize my MCP/API (sellers) | npx create-lemon-mcp → add a Seller Key in /app to go live | | Add billing to a server I already have | @lemon-cake/mcp-sdk — wrap a tool with lc.charge(), or route through the gateway (no code) | | Let an agent pay for paid APIs (buyers) | npx -y agent-payment-mcp — 8 free demo tools, no signup |

<details> <summary>Buyer-side MCP — try in 30 seconds</summary>

npx -y agent-payment-mcp

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

Ask your agent to run list_demos / call_demo. To call paid APIs, set LC_PAY_TOKEN (get one at lemoncake.xyz/app).

</details>

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What is LemonCake?

LemonCake is an x402 payment rail for monetizing MCP servers and HTTP APIs. Sellers register an endpoint and set a price per call. Buyers prepay by card and receive a spend-capped Pay Token. Agents call the gateway with that token, and LemonCake verifies, meters, forwards, and records usage.

sequenceDiagram
    participant A as 🤖 AI Agent
    participant G as 🍋 LemonCake Gateway
    participant API as Your API
    A->>G: POST /g/:id (no token)
    G-->>A: 402 + accepts[] (price, mintUrl)
    A->>G: mint Pay Token (off-session, capped)
    A->>G: Bearer :jwt
    G->>API: forward (upstream key hidden)
    API-->>A: 200 + result
    Note over A,G: budget exhausted → 402 → agent self-funds → continues

Sellers register any HTTP API and set a price per call. Buyers / agents prepay with a card → Pay Token issued automatically → agent calls the API within budget. Budget exhausted → 402 challenge → agent self-funds → continues. No humans.

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🧱 Open core

| Layer | Status | Where | |---|---|---| | Buyer-side MCP (agent-payment-mcp) | ✅ MIT | npm, src | | Seller SDK (@lemon-cake/mcp-sdk) | ✅ MIT | npm, src | | Starter templates | ✅ MIT | examples/ | | Docs site | ✅ Public | lemoncake.xyz/docs | | Gateway + billing engine | 🔒 Hosted | lemoncake.xyz | | Dashboard (analytics, usage ledger) | 🔒 Hosted | lemoncake.xyz/app |

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💳 How payment works

For buyers (human or agent)

Open a buy link (lemoncake.xyz/buy/<shortId>)
Pay with a card → Pay Token (JWT) issued automatically
Pass Authorization: Bearer <token> to the gateway
Gateway verifies, meters, forwards to the real API
Budget exhausted → 402 challenge returned with payment instructions

For agents (fully autonomous)

Issue a Buyer Key (bk_...) at /app → Pay Tokens pane
Save a card once at /agent/fund
Agent calls POST /api/lc/agent/tokens (Bearer bk_) → off-session card charge → JWT
Agent uses JWT to call gateway — hard-capped, no human in the loop

// MCP config for agent with pre-issued Pay Token
{
  "mcpServers": {
    "lemon": {
      "command": "npx",
      "args": ["-y", "agent-payment-mcp"],
      "env": {
        "LC_PAY_TOKEN": "<jwt from Pay Token>"
      }
    }
  }
}

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🏗 Publish your API on LemonCake (sellers)

Monetize any HTTP API or MCP server:

Sign in at lemoncake.xyz/app
Add API — paste your URL, set price per call (e.g. $0.01)
Share the buy link, or issue a Seller Key (sk_live_…) to charge from your own server
You keep 97%. LemonCake takes 3% (Stripe Connect Direct Charge). Never holds funds.

Scaffold a paid MCP in one command — sandbox by default, production with one env var:

npx create-lemon-mcp my-paid-mcp     # demo runs with no key
# then: set LEMONCAKE_SELLER_KEY=sk_live_… → it charges for real (no code change)

Add billing to any tool with the SDK (@lemon-cake/mcp-sdk v1, no crypto):

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

const lc = createLemonCakeSDK();   // reads LEMONCAKE_SELLER_KEY (demo without it)

server.tool("my_premium_tool", "desc", { q: z.string() },
  lc.charge({ price: 0.01 })(async ({ q }) => {
    return { content: [{ type: "text", text: "result" }] };
  }),
);

lc.charge wraps the handler: preflight (reserve) → run → settle (confirm on success, refund on failure). Or route existing traffic through https://lemoncake.xyz/g/<shortId> — no code changes required.

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🪪 Agent Identity

Give each AI agent its own spend-capped identity — so a fleet can pay for APIs without a shared card or runaway cost. Built on top of Pay Tokens; no balance pool, custody-free (an agent's "budget" is just the Pay Tokens bound to it).

Bind a Pay Token to an agent when issuing it (agentId) → spend is attributed to that agent.
Per-agent rollup — budget, spend, calls, last-used in the dashboard.
Kill switch — pause / resume / revoke an agent; bound tokens are rejected at the gateway instantly (AGENT_PAUSED / AGENT_REVOKED), even with budget remaining.
Server-authoritative — price is set on the endpoint; agents never carry a card or a seller key.

# manage agents (owner-authenticated)
POST /api/agents            # create  → { agent_id, ... }
POST /api/agents/:id/pause  # kill switch (also /resume, /revoke)
GET  /api/agents            # list + per-agent spend rollup

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✨ Features

For agents / buyers

✅ x402 native — 402 challenge returns accepts[] with price + mintUrl
✅ Hard-capped — per-mint / daily / monthly limits, server-enforced
✅ Off-session top-up — agent self-funds via Buyer Key (bk_...), no prompts
✅ Demo Mode — 8 free tools, try without any setup

For API providers / sellers

✅ 5-min go-live — npx create-lemon-mcp, or lc.charge() on any tool, or route through the gateway
✅ Custody-free — Stripe Connect Direct Charge, 97% goes directly to seller
✅ Usage ledger — every call recorded, revenue visible in dashboard
✅ Buy link — share one URL, buyers self-serve

For agent fleets / operators

✅ Per-agent identity — bind Pay Tokens to an agent, attribute spend
✅ Per-agent kill switch — pause / resume / revoke, enforced at the gateway
✅ Spend rollup — budget / spent / calls per agent
✅ No balance pool — custody-free; budget = the agent's bound Pay Tokens

Infrastructure

🔧 Stripe Connect Direct Charge (no custody)
🔧 x402 gateway with WWW-Authenticate: Lemoncake-Prepaid
🔧 EN / 日本語 / Español dashboard
🔧 JP FSA: registration not required (confirmed 2026-06)

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🏗 Architecture

┌─────────────────────────────────────────────────┐
│  Buyer / Agent                                  │
│   ↳ prepays via card OR Buyer Key (bk_...)      │
│   ↳ receives Pay Token (signed JWT)             │
└──────────────────────┬──────────────────────────┘
                       │  Authorization: Bearer <jwt>
                       ▼
┌─────────────────────────────────────────────────┐
│  LemonCake Gateway  /g/<shortId>                │
│   ↳ verify JWT signature                        │
│   ↳ check budget + calls + rate limit           │
│   ↳ decrement spend, write to ledger            │
└──────────────────────┬──────────────────────────┘
                       │  HTTPS + upstream_auth (hidden)
                       ▼
┌─────────────────────────────────────────────────┐
│  Your API / MCP server (unchanged)              │
└─────────────────────────────────────────────────┘

LemonCake is the middle box. It never holds funds — money flows Stripe → seller via Direct Charge.

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🌍 Compliance

Japan FSA Fintech Support Desk (2026-06) confirmed: no registration required. Custody-free design (Stripe Connect Direct Charge, no pooled balance).

| Jurisdiction | Basis | |---|---| | 🇯🇵 Japan | FSA — 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 |

See lemoncake.xyz/security

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🔌 Package family

| Package | What it does | |---|---| | agent-payment-mcp | Main entry — x402 gateway + agent payment rail | | @lemon-cake/mcp-sdk | Seller SDK — lc.charge() / lc.protect(), fiat, no crypto | | create-lemon-mcp | Scaffold a paid MCP server — sandbox→prod with one env var | | xstocks-mcp | Buy tokenized US stocks on Solana | | alpaca-guard-mcp | Alpaca paper / live trading with hard daily cap | | tokenized-stock-mcp | Dinari dShares |

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🛡 Security

Server-side hard caps — per-mint / daily / monthly, cannot be exceeded
Pay Token = signed JWT — HS256, verified on every gateway call
upstream_auth never exposed — seller's real API key hidden from buyers
RLS on all DB tables — Supabase row-level security enabled
Stripe Connect Direct Charge — LemonCake never holds funds

agent-payment-mcp