MiniDex - Stablecoin Mini DEX

A minimal, gas-efficient decentralized exchange for stablecoin swaps on Base Chain Mainnet.

Overview

MiniDex is a single-pool AMM designed exclusively for USDC/USDT swaps with near-zero slippage. The design prioritizes simplicity, readability, and correctness over feature richness.

Key Features

• Single Pool: USDC/USDT only
• Near-Zero Slippage: Optimized stable-swap curve
• Fixed Swap Fee: 0.0000015 ETH per swap
• Minimal Design: No governance, no upgrades, no pause logic
• Gas Efficient: Optimized for low transaction costs

Contract Addresses (Base Mainnet)

Contract	Address
USDC	0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913
USDT	0xfde4C96c8593536E31F229EA8f37b2ADa2699bb2
StablePool	0x47f4b9bDbaa5e1fB2fC4cCac446610456B406BCC

AMM Math Explanation

The Stable-Swap Invariant

MiniDex uses a simplified stable-swap formula optimized for stablecoin pairs. The approach combines two AMM models:

1. Constant-Sum (x + y = k)

• Perfect for pegged assets
• Zero slippage at all trade sizes
• Problem: Can be fully drained in one direction

2. Constant-Product (x * y = k)

• Used by Uniswap V2
• Provides infinite liquidity depth
• Problem: High slippage for stablecoin swaps

Our Hybrid Approach

We use an amplified weighted average of both models:

amountOut = (A * constantSumOut + constantProductOut) / (A + 1)

Where:

• A = 100 (amplification coefficient)
• constantSumOut = amountIn (1:1 exchange)
• constantProductOut = amountIn * reserveOut / (reserveIn + amountIn)

Effect: With A=100, approximately 99% of the output follows constant-sum behavior (1:1), while 1% follows constant-product for safety at extreme imbalances.

Mathematical Properties

For a balanced pool with 100,000 USDC and 100,000 USDT:

Swap Size	Slippage
$100	< 0.01%
$1,000	< 0.1%
$10,000	< 1%

Decimal Handling

Both USDC and USDT use 6 decimals. Internally, we normalize to 18 decimals for calculations:

uint256 normalizedAmount = rawAmount * 10^(18 - tokenDecimals)

Frontend

The frontend is a simple web interface for interacting with the DEX.

Running the Frontend

# Install dependencies
cd frontend
npm install

# Start development server
npm run dev

The frontend will be available at http://localhost:5173

Features

• Connect wallet (MetaMask, etc.)
• Swap USDC ↔ USDT
• Add/Remove liquidity
• View pool reserves
• Real-time price calculations

Integration Guide

JavaScript/TypeScript

import { ethers } from 'ethers';

const POOL_ADDRESS = '0x47f4b9bDbaa5e1fB2fC4cCac446610456B406BCC';
const SWAP_FEE = ethers.parseEther('0.0000015');

// Swap USDC to USDT
async function swap(signer, amountIn, minAmountOut) {
  const pool = new ethers.Contract(POOL_ADDRESS, POOL_ABI, signer);
  
  // Approve USDC first
  await usdc.approve(POOL_ADDRESS, amountIn);
  
  // Execute swap
  const tx = await pool.swap(
    USDC_ADDRESS,
    amountIn,
    minAmountOut,
    { value: SWAP_FEE }
  );
  
  return tx;
}

Reading Pool State

// Get reserves
const [reserveUSDC, reserveUSDT] = await pool.getReserves();

// Get expected output
const amountOut = await pool.getAmountOut(USDC_ADDRESS, amountIn);

Security Considerations

Implemented Protections

1. Reentrancy Safety: State updated before external calls
2. Slippage Protection: minAmountOut parameter on swaps
3. Safe ERC20: Handles non-standard tokens (USDT)
4. Input Validation: All inputs validated with clear revert messages
5. No Upgrades: Immutable contract, no proxy pattern
6. No Admin Functions: Cannot be rugged by owner

Known Limitations

1. No Oracle: Assumes 1:1 peg, vulnerable to depeg events
2. Single Pool: No routing, only USDC/USDT
3. Fixed Fee: Cannot adjust fee without redeployment
4. No Flash Loans: Not implemented

Gas Estimates

Operation	Estimated Gas
swap	~80,000 - 100,000
addLiquidity	~120,000 - 150,000
removeLiquidity	~100,000 - 130,000

Project Structure

miniDex/
├── src/
│   ├── StablePool.sol      # Main AMM contract
│   ├── LPToken.sol         # LP token (ERC20)
│   └── interfaces/
│       ├── IERC20.sol      # ERC20 interface
│       └── IStablePool.sol # Pool interface
├── frontend/               # Web frontend
│   ├── index.html
│   ├── src/
│   │   └── app.js
│   └── package.json
├── foundry.toml            # Foundry config
└── README.md               # This file

License

MIT License