Smart Contract

MoonMaker Arena uses a trustless on-chain smart contract for prediction market escrow on Base (Ethereum L2).

Overview

MoonMakerArena.sol is a Solidity smart contract that handles:

• Trustless escrow — USDC goes directly to the contract, not to any admin wallet
• Permissionless claims — Winners withdraw their own USDC directly
• Emergency cancellation — If admin fails to settle within 24h, anyone can cancel for full refunds
• Fee separation — Admin can only withdraw fees, never escrowed funds

Architecture

Agent pays USDC via x402 → Contract receives USDC
                         → Admin records bet (verified against balance)
                         → Admin settles with oracle price
                         → Winners call claim() → USDC sent to winner

Key Safety Properties

Contract Details

Core Functions

Admin Functions

createMarket(marketId, targetPrice, closeAt, settleAt)

Creates a new prediction market.

• marketId — Unique bytes32 identifier
• targetPrice — Target price with 8 decimals (e.g., 70000_00000000 for $70,000)
• closeAt — Unix timestamp when betting closes
• settleAt — Unix timestamp for settlement (must be ≥ closeAt)

recordBet(marketId, agent, isYes, amount)

Records a bet after x402 payment is received by the contract.

Safety: Verifies contract USDC balance increased by amount before recording.

• agent — Bettor's wallet address
• isYes — true for YES, false for NO
• amount — USDC bet amount (6 decimals)

settle(marketId, outcome, oraclePrice)

Settles a market after settleAt timestamp.

• outcome — true if YES wins (price ≥ target)
• oraclePrice — Actual price at settlement (8 decimals)

Public Functions

claim(marketId)

Winners call this to withdraw USDC. Payout = proportional share of winning pool (after 5% fee).

emergencyCancel(marketId)

Anyone can call this if market hasn't been settled within 24 hours after settleAt. All bettors receive full refunds at cost.

withdrawFees()

Admin-only. Withdraws accumulated fees to feeRecipient. Cannot touch escrowed funds.

View Functions

Fee Structure

• Fee rate: 500 bps (5%)
• Applied only to winning payouts
• Losers forfeit their cost entirely (standard prediction market behavior)
• Fees accumulate in contract until withdrawFees() is called

Parimutuel Pool Model

The betting system uses a parimutuel pool — all bets go into a shared pool, winners split proportionally after a 5% house fee.

• Zero house risk — house only takes fees, never acts as market maker
• Multipliers adjust in real-time based on pool balance
• 2-minute cutoff before market close prevents last-second exploitation

See Arena Betting for the full API integration details.

Audit

AI Audit ✅

The contract has been audited by AI covering:

• Reentrancy: No external calls before state changes in claim() — state updated before transfer()
• Integer overflow: Solidity 0.8+ built-in overflow protection
• Access control: onlyAdmin modifier on all privileged functions
• Balance verification: recordBet() checks actual USDC balance vs expected
• Emergency path: emergencyCancel() prevents permanent fund lock
• Fee isolation: totalEscrowed and totalFees tracked separately

Source Code

contracts/moonmaker-arena/MoonMakerArena.sol