Playground

Paid MCP/API calls in 30 seconds.

Mint a sandbox Pay Token, send one metered call, and see the seller ledger update. No account, card, or crypto wallet required.

Budget left

$0.20

Calls left

Seller share

97%

Mint Pay Token

$0.20 cap, 20 calls, expires in 1 hour.

Run metered call

Gateway verifies the token before forwarding.

Live event log

Gateway checks

$0 real funds

Sandbox ready

Demo endpoint is priced at $0.01 per call.

Pay Token issued

Click mint to create a bounded credential.

Gateway verified

Run a metered call to verify the token.

Seller ledger updated

Revenue appears here after a successful call.

Cap enforced

When the budget runs out, the gateway refuses with 402.

Seller ledger

Usage and revenue

Revenue

$0.00

Calls

Fee

Net

$0.00

Run a call to create the first ledger row.

Use it from code

Same call, three ways

curl -s -X POST https://www.lemoncake.xyz/g/{shortId} \
  -H "Authorization: Bearer $LC_PAY_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"ping":1}'

In production, the buyer pays by card and the agent receives a spend-capped Pay Token.

Ready to make your own endpoint paid?

One command scaffolds a paid MCP server — sandbox now, production with one env var. First 3,000 lifetime calls are free, then LemonCake takes 3%.

Docs Open dashboard →

How this playground works

The playground runs the same three-step flow a real AI agent uses to pay for an API with LemonCake: it mints a spend-capped Pay Token (a prepaid-card-like credential with a hard budget, expiry, and endpoint scope), pays $0.01 per call through the live x402 gateway, and stops with HTTP 402 the moment the budget runs out. Everything is sandboxed — no login, no card, no crypto wallet — but the gateway checks are the production code path.

Step 1

Mint a sandbox Pay Token

One click issues a spend-capped sandbox credential. The cap, expiry, and scope are baked into the token itself — the agent holds no wallet and no API key.

Step 2

Run a metered call

Fire a $0.01 paid call. The gateway verifies the token, reserves the charge atomically, forwards the request, and settles — each check appears in the live event log.

Step 3

Hit the cap, get a 402

Keep calling until the budget drains. The gateway blocks the next call with HTTP 402 (cap_enforced) before it reaches the seller's API; the ledger shows usage and 97% seller revenue per call.

Frequently asked questions

What is the LemonCake Playground?

A free sandbox that demonstrates AI-agent payments end to end: it mints a spend-capped Pay Token, runs a metered $0.01 API call through the live LemonCake x402 gateway, and shows the seller ledger updating in real time. There is no login, no credit card, and no crypto wallet — sandbox tokens mirror production behavior without moving real funds.

What is a Pay Token?

A Pay Token is a spend-limited payment credential a buyer hands to an AI agent — like a prepaid card with a hard budget cap, expiry, and endpoint scope baked in. The gateway verifies it on every call and rejects anything over the cap with HTTP 402, so a runaway agent can never overspend.

Is real money involved in this demo?

No. The playground uses sandbox Pay Tokens that behave exactly like production ones — budget checks, metering, and 402 enforcement all run on the real gateway — but no card is charged and no funds move.

What happens when the Pay Token budget runs out?

The gateway returns HTTP 402 Payment Required and blocks the call before it reaches the seller's API. The demo shows this as the cap_enforced event: the agent simply stops, with no surprise bills on either side.

How do I make my own API or MCP server paid?

Paste your endpoint URL in the LemonCake dashboard (no code changes), or scaffold a new paid MCP server with npx create-lemon-mcp. Set a per-call price — sub-cent from $0.005 works — and share the buy link. Your first 3,000 calls are free, then LemonCake takes 3% and sellers keep 97%, paid out via Stripe.

Does the demo work with MCP clients like Claude?

Yes. The playground's "Use it from code" panel gives you the same call as curl, as an MCP server config you can paste into any MCP client, and as an SDK snippet. LemonCake is drop-in middleware for any MCP server and works with any MCP SDK.

Ready to charge for your own endpoint? Paste your URL in the dashboard or scaffold a paid MCP server with npx create-lemon-mcp. First 3,000 calls free, then 3% — see pricing and how LemonCake works.