Paddles In

The group chat assistant that gets the organizer paid back.

getpaddlesin.com · ▶ Watch the demo (under 3 min) · Try it on your phone · For judges · For AI reviewers

One friend books the court and pays for it, then spends the week asking everyone for $8. Paddles In does that job for them. A hold makes "I'm in" mean something, a late drop is the organizer's call, and the money comes back without anyone having to ask.

Try it (judges)

1. Open getpaddlesin.com/demo on a laptop and scan the code with your phone. You're the organizer.
2. Follow the steps on the page. Friends join in the group chat, then you switch to a player and tap I'm in.
3. Approve the hold on a computer (PayPal's sandbox checkout doesn't run on phones), signing in as the PayPal sandbox buyer shown on the /demo page and in JUDGES.md. That hold is real, in PayPal's sandbox.
4. Move the clock past the game and settle. You'll see the player charged only their share, and the organizer paid back.

No phone handy? /play runs the same game in one browser tab.

How it works

Drop out early and your hold is simply released. Drop out late and the organizer decides, privately, whether to charge you or cover it. Nobody's money is ever talked about in the group.

What we used, and why

	What it does here, in one sentence
PayPal holds	Saying "I'm in" puts a hold on your money, like a deposit, so your spot is real but nothing is spent yet.
PayPal partial capture	After the game, PayPal takes only your share and gives back the rest of the hold.
PayPal refunds	If someone took your spot after you were charged, the organizer can give your money back in one tap.
PayPal Payouts + Venmo	All the money collected goes back to the organizer's Venmo or PayPal in one payment.
PayPal webhooks	PayPal tells us when something changes, like a hold running out, so our records always match.
Claude (Anthropic)	Claude reads the group chat and works out what people mean, like "yeah I'm down" or "can Lee take my spot?".
Plain code for money	Claude never decides an amount or moves money. Fixed rules in our code do that.
Render	Render runs the website and keeps the database of games and players.
Render Workflows	Render Workflows does the jobs nobody should have to remember: reminders, renewing holds, and settling up after the game.
Sendblue	Sendblue lets the assistant send and receive real text messages.
Next.js	Next.js builds the game pages people open from the chat.

Proof from a real sandbox run

Game thu-6pm-7f1ff on 2026-11-13, court $64.00. Every id below is a real PayPal sandbox object.

Step	PayPal API	PayPal id	Detail
Hold placed	Orders v2 intent: AUTHORIZE	09E08340UY454690Y	Jo, $10.00 order
Hold authorized	/v2/checkout/orders/{id}/authorize	3LW67805SM430330M	Jo, $10.00 held
Share charged	/v2/payments/authorizations/{id}/capture (partial)	8B0352900S458142Y	Jo, $10.00 of $10.00 held

Verified webhooks received: CHECKOUT.ORDER.APPROVED (1), PAYMENT.AUTHORIZATION.CREATED (1), PAYMENT.CAPTURE.COMPLETED (1).

What's real: Claude reading every message, the game pages, any hold you approve with a sandbox buyer, and the payout. What's simulated: the other players in the demo and their holds (ids start with SIM-), so a game can fill in seconds.

For AI reviewers

The full technical brief is in docs/AI-REVIEWERS.md: what to read first, the message pipeline, every PayPal call with its idempotency key, the money invariants and how the system recovers. In short:

• Claude reads, code pays. Claude (claude-haiku-5-5, forced tool calls) only picks one of 14 fixed actions. Deterministic code in src/bot/assistant.ts sets every amount and makes every PayPal call.
• Eight PayPal operations: create order (AUTHORIZE), authorize, void, reauthorize, partial capture, refund, payout, and webhook verification. Every write sends a PayPal-Request-Id derived from the object it acts on.
• Safe to run twice. Settling claims the game row before charging, webhooks apply once, and Render Workflows finishes anything a restart cut off.
• Checked on every PR: typecheck, lint, unit tests and build in CI.

Run it yourself

cp .env.example .env      # PayPal sandbox keys, ANTHROPIC_API_KEY, DATABASE_URL
pnpm install
pnpm dev                  # http://localhost:3000/play

Webhooks, payouts, Sendblue, Render Workflows and deploy: docs/SETUP.md.

Credits

MIT licence. Built for the PayPal AI Hackathon 2026 with PayPal's developer sandbox, Claude (Anthropic), Next.js and Render; Claude Code helped write the code. Design patterns studied on Mobbin, then redrawn from scratch. Fonts: Figtree and Barlow Condensed (SIL Open Font License).