Ajo

Join a savings circle with Face ID. No wallet, no treasurer, one passkey.

Ajo is an ajo/esusu rotating savings circle on Monad. A contract holds the pot, members sign in with a passkey through Mera, and every circle gets its own key.

Live ↗ · Verify it yourself ↗

Built for the Monad Metropolis hackathon (Track 02, Consumer Products & Payments).

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The problem

• The treasurer. In a traditional ajo one person holds everyone's cash. If they stall, spend it or disappear, every payout waits.
• The missed round. One member who stops paying delays the whole group, and nobody has a way to cover the gap.
• The wallet wall. Most people who would join a circle have never installed a crypto wallet.

What Ajo is

Each round every member pays the same amount, and one member collects the pot, in join order, until everyone has had a turn.

JOIN → PAY → CLOSE ROUND → COLLECT → GET COLLATERAL BACK

1. Join. Open an invite link, sign in with a passkey. Mera turns the passkey into a wallet, and the app locks one extra contribution as collateral.
2. Pay. Each member pays once per round, inside the round window. The contract rejects late and double payments.
3. Close round. Anyone can close a round once everyone has paid or the window ends. If someone missed it, their collateral covers the gap.
4. Collect. The member whose turn it is receives the pot.
5. Finish. When the last round closes, leftover collateral is withdrawable.

One passkey makes one 24-word recovery phrase (button: "Back up my keys"). Index 0 is the main wallet and each circle uses its own key, so the same phrase opens every account in MetaMask or Rabby.

Verify it yourself in 60 seconds

No wallet and no key needed. You need Foundry. Expected results below came from runs made before they were written here.

git clone https://github.com/yonkoo11/ajo-circle && cd ajo-circle/contracts
forge install foundry-rs/forge-std --no-git
forge test                     # → 11 passed; 0 failed; 0 skipped
cast chain-id --rpc-url https://testnet-rpc.monad.xyz   # → 10143
cast call 0xd2cad31A080b0daE98d9d6427e500B50bCb92774 "getCircle(uint256)" 4 \
  --rpc-url https://testnet-rpc.monad.xyz
# → contribution 1000000 (0xf4240), size 2, roundSeconds 240, round 2 (finished), 2 members

The tests cover a full cycle, a defaulting member, a repeat defaulter, late payment, double payment, an outsider paying, closing early, joining twice or after start, early collateral withdrawal and a re-entrant token. The chain read shows a two-member circle that ran every round to the end. It does not prove anything about a real group, real money or mainnet.

What's real, and what we deliberately did not claim

Capability	Status
Circle contract	Real. 11 of 11 tests pass; deployed on Monad testnet.
Two-member circle, start to finish	Real. Circle 4 ran two rounds and its final balances matched the expected payouts.
Passkey sign-up and create circle on the live site	Real. Done in desktop Chrome with a passkey saved to Google Password Manager.
Gas for new wallets	Real on testnet. A faucet endpoint sends 0.1 MON per new wallet.
Second person joining through the invite link in the UI	Real, in scripted headless Chrome with virtual passkeys: circle 6 and circle 8 each ran join, pay and close round with two users. Not yet done by two people on two phones.
Returning-user sign-in on the live site	Real in the same scripted run ("Unlock with Face ID"). Not yet tried on a real phone.
Token	Testnet uses a mock token with an open mint. Mainnet AUSD exists on Monad (6 decimals) but this app has not run against it.
Mainnet	Not deployed.
Yield on the idle pot	Not built.
Independent security audit	None. Do not put real savings in it.
Real savings groups using it	None yet.

Project layout

contracts/
  src/AjoCircle.sol      # the circle: create, join, pay, close round, collateral
  test/                  # 11 tests, mock token, a re-entrant token
  script/                # deploy and two-member run scripts
app/
  src/wallet.ts          # Mera passkey sign-in, key per circle, recovery phrase, signing
  src/App.tsx            # screens: welcome, create, join, circle, recovery
  api/drip.js            # testnet gas faucet for new wallets

Run it locally

cd app && npm install      # install
cp .env.example .env.local  # the deployed testnet contract addresses
npm run build              # type-check and bundle the site
npm run dev                # start it at localhost

Passkeys need a secure origin, so use localhost or the live site. Desktop Chrome needs the passkey saved to Google Password Manager, or sign-in fails with a clear message.

Tech stack

• Contract: Solidity, Foundry · App: Vite, React, TypeScript, viem · Passkeys: @category-labs/mera · Chain: Monad testnet (10143) · Site: Vercel

License

MIT, see LICENSE.