🍋 LemonCake — Billing & budgets for AI agents
by evidai
README.md
# 🍋 LemonCake — agent-payment-mcp
**Let your AI agent pay for any API — capped, no account.**
Give your agent a spend-capped Pay Token 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.
Want to monetize your own MCP server or API? Start at [lemoncake.xyz/app](https://lemoncake.xyz/app) or copy the [mcp-monetization-starter](../examples/mcp-monetization-starter).
[](https://www.npmjs.com/package/agent-payment-mcp)
[](https://www.npmjs.com/package/agent-payment-mcp)
[](https://glama.ai/mcp/servers/evidai/lemon-cake)
[](https://registry.modelcontextprotocol.io)
[](https://x402.org)
[](https://lemoncake.xyz/security)
[](https://lemoncake.xyz/pricing)
> 💰 **No monthly fee. First 3,000 calls free (lifetime). Then 3% only when your API earns.**
> [See pricing →](https://lemoncake.xyz/pricing)
---
## ⚡ Try in 30 seconds — no signup
Add to `~/Library/Application Support/Claude/claude_desktop_config.json` (or Cursor / Cline):
```json
{
"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](https://x402.org) — 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)
↓
Bearer <jwt> → gateway → your API
```
1. **Seller** registers any HTTP API at [lemoncake.xyz/app](https://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](https://lemoncake.xyz/app)
2. Save a card once at [/agent/fund](https://lemoncake.xyz/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](https://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).
```typescript
// 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](https://lemoncake.xyz/security)
---
## 🔌 The LemonCake family
| Package | Use |
|---|---|
| [`agent-payment-mcp`](https://www.npmjs.com/package/agent-payment-mcp) | **Main MCP** — x402 gateway + agent payment rail (this one) |
| [`@lemon-cake/mcp-sdk`](https://www.npmjs.com/package/@lemon-cake/mcp-sdk) | SDK to monetize your own MCP server |
| [`xstocks-mcp`](https://www.npmjs.com/package/xstocks-mcp) | Buy tokenized US stocks on Solana |
| [`alpaca-guard-mcp`](https://www.npmjs.com/package/alpaca-guard-mcp) | Alpaca paper / live trading with hard USD cap |
| [`tokenized-stock-mcp`](https://www.npmjs.com/package/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 customer funds.
- **RLS on all DB tables**, `upstream_auth` never returned in API responses.
---
## Links
| | |
|---|---|
| **Try demo** | `npx -y agent-payment-mcp` or [lemoncake.xyz/demo](https://lemoncake.xyz/demo) |
| **Seller dashboard** | [lemoncake.xyz/app](https://lemoncake.xyz/app) |
| **Agent card setup** | [lemoncake.xyz/agent/fund](https://lemoncake.xyz/agent/fund) |
| **Docs** | [lemoncake.xyz/docs](https://lemoncake.xyz/docs) |
| **Source** | [github.com/evidai/agent-payment-mcp](https://github.com/evidai/agent-payment-mcp) |
| **MCP Registry** | [registry.modelcontextprotocol.io](https://registry.modelcontextprotocol.io) |
| **License** | MIT |
TDQS
A4.7/5.0
Scored across 6 tools
Disambiguation5/5
Each tool has a clearly distinct role: setup guides onboarding, list_services discovers offerings, call_service executes paid calls, check_balance monitors funds, check_tax handles compliance, and get_service_stats provides marketplace analytics. There is no meaningful overlap or ambiguity between them.
Naming Consistency5/5
Tool names follow a consistent snake_case verb_noun pattern: list_services, call_service, check_balance, check_tax, get_service_stats. Even 'setup' fits as a single-word imperative without breaking the overall stylistic consistency.
Tool Count5/5
Six tools is a well-scoped count for a billing/proxy service: onboarding, discovery, execution, balance checking, tax compliance, and usage stats each earn their place. The server feels neither bloated nor thin.
Completeness4/5
The core lifecycle is well covered: discover services, call them, check balance, and verify tax obligations. Minor gaps exist, such as no explicit transaction-history or budget-configuration tool, but the daily cap and receipt fields mitigate these and the main workflows are complete.
Maintenance
ActivityInactive
ResponsivenessWithin a week