🍋LemonCake
MCP server · USDC · x402-compatible · agent payments

Pay-per-call USDC for any HTTP API.

Give your AI agent a wallet. Your Claude / Cursor / Cline calls Tavily, ElevenLabs, gBizINFO — without you handing over API keys. Per-call billing in USDC, refunds on failure, capped spending.

Paste into any terminal. With no environment variables, it boots in Demo Mode — real Wikipedia / FX / httpbin, no signup, no card.

Try in browser sandbox →How it works
MIT licensedMCP 1.10+Node 20+Listed on GlamaDemo Mode (no auth)x402-compatible

↑ live capture · this is what `npx -y pay-per-call-mcp` actually outputs

Live demo

Try it on this page — no install, no signup

The widget below hits the same Wikipedia / FX / httpbin upstreams that npx -y pay-per-call-mcp uses in Demo Mode. Same response shape, same x402-compatible receipt, $0 charged. If this convinces you the call shape is right, install the MCP server and your agent gets the same JSON back.

Wikipedia search via opensearch API. Hits real en.wikipedia.org · same response as call_service(serviceId="demo_search") from npx -y pay-per-call-mcp.

This widget hits the same upstream as the published MCP server — no signup, no Pay Token, $0 charged. Switch to a real service ($0.005/call typical) by setting LEMON_CAKE_PAY_TOKEN after creating an account.

The friction we kill

Why this exists

Stop juggling API keys.

Your agent shouldn't need 12 different SaaS dashboards. One Pay Token covers Tavily, Serper, ElevenLabs, gBizINFO, Hunter.io — the upstream secret stays with us.

Stop manual signups.

Every new API needs an email, a card, a quota tier. With pay-per-call, your agent calls a service for $0.005 and gets the result. No relationship to set up.

Stop overspending.

KYA (Know-Your-Agent) limits cap your agent's spend per session, per day, per service. Issue a token with a $5 ceiling and walk away.

How it works

30-second walkthrough

  1. 01

    Run the MCP server (no signup)

    Add this to claude_desktop_config.json (or your Cursor / Cline equivalent):
    {
  "mcpServers": {
    "pay-per-call": {
      "command": "npx",
      "args": ["-y", "pay-per-call-mcp"]
    }
  }
}

    No env vars = Demo Mode. Boot the Inspector and call demo_search to hit real Wikipedia results.

  2. 02

    Ask Claude to use it

    Open Claude Desktop and type:

    "Search Wikipedia for ‘Model Context Protocol’ via pay-per-call-mcp and summarise."

    Claude picks call_service, fires demo_search, returns the summary. No API key required.

  3. 03

    Top up to unlock paid services

    Add LEMON_CAKE_PAY_TOKEN to the env block above and your agent can call Tavily, Serper, Hunter.io, the NTA invoice API, gBizINFO, and more — billed in USDC, $0.005/call typical, 10% platform margin.

    Create a free account →

Try without typing

Pre-written prompts

The MCP server ships with 6 ready-to-fire prompts. They show up in the Glama Inspector / Claude Desktop / Cursor prompt picker. Click one and the agent runs the full demo flow.

🎮explore-demo

setup → list_services → demo_search → demo_fx, no auth needed

🛍discover-marketplace

List approved services and recommend top 3 for an agent's use case

🇯🇵japan-tax-check

Validate 適格請求書発行事業者番号 against the NTA registry

💰spend-with-budget

check_balance → call_service → check_balance, see KYA caps in action

🔄real-vs-demo

Hit demo_search and a real Serper service with the same query

🏯japan-finance-bundle

gBizINFO + 国税庁 + e-Gov bundled Japan-corp research workflow

Cost

Transparent pricing

Per call

$0.005

typical price for search / API services

Platform margin

10%

we resell upstream APIs at +10% — that's the whole pricing

Minimum top-up

$5

USDC or JPYC. No subscription. No expiry.

Standards

x402-compatible interface

Settlement happens off-chain via your Pay Token, but the response shape mirrors the x402idiom. Write your agent's payment-handling logic once and ship it unchanged when on-chain auto-pay (gated on issue #4) lands.

✓Receipt on success

`x402Receipt` field with scheme / chain / asset / amount / recipient / paymentIntentId / settledAt — same parser works for on-chain x402.

✓402 challenge parser

Detects WWW-Authenticate: x402, X-402-* headers, and body.x402. Surfaced as `x402Challenge` with source attribution.

✓PAYMENT_PENDING retry

Async settlement returns retryAfterMs + retryContract; same idempotencyKey resumes without double-charge.

{
  "status": 200,
  "chargeId": "ch_abc123",
  "amountUsdc": "0.005",
  "x402Receipt": {
    "scheme":         "lemoncake-pay-token-v1",
    "x402Compatible": true,
    "asset":          "USDC",
    "amount":         "0.005",
    "recipient":      "serper",
    "paymentIntentId":"ch_abc123",
    "settledAt":      "2026-05-09T14:50:11.019Z"
  }
}

Demo Mode emits the same shape — write your handler against demo_search and ship unchanged.

Differentiator

Japanese tax & corporate APIs (built-in)

Most agent payment infrastructure ignores Japan. We don't. Native MCP tools for inbound JP business compliance:

  • ✓国税庁 適格請求書発行事業者番号 検証/ NTA invoice issuer verification
  • ✓gBizINFO 法人情報/ gBizINFO corporate registry
  • ✓e-Gov 法令検索/ e-Gov statutes search
  • ✓TRUSTDOCK eKYC/ TRUSTDOCK eKYC
  • ✓源泉徴収判定 + 計算/ Source-withholding ruling + calculation
  • ✓freee / Money Forward 仕訳出力/ freee / MF journal export

The japan-tax-check and japan-finance-bundle prompts wrap these into one-click flows.

Ship an agent that pays for itself.

Demo Mode runs in 30 seconds. Real services unlock with a $5 top-up. No subscription, MIT-licensed source.

Try in browser sandbox →Create free account