Uniswap Swap Simulation

Simulate and analyze Uniswap swaps including price impact, slippage, optimal routing, and gas estimation. Use when the user asks about swap execution, routing, price impact, or MEV considerations.

Overview

This skill covers simulating Uniswap swaps, calculating price impact, and analyzing routing decisions.

Key Concepts

• Price Impact: The change in pool price caused by a swap. Larger swaps have higher impact.
• Slippage: Difference between expected and executed price, including price movement between submission and execution.
• Routing: Finding the optimal path across pools and protocols for best execution.

Simulating a Swap

Use the Quoter contract to simulate swaps without executing:

typescript

import { createPublicClient, http, encodeFunctionData } from "viem";

// QuoterV2 for v3 pools
const quote = await client.readContract({
  address: quoterV2Address,
  abi: quoterV2Abi,
  functionName: "quoteExactInputSingle",
  args: [
    {
      tokenIn,
      tokenOut,
      amountIn,
      fee,
      sqrtPriceLimitX96: 0n,
    },
  ],
});

// Returns: [amountOut, sqrtPriceX96After, initializedTicksCrossed, gasEstimate]

Price Impact Calculation

typescript

function calculatePriceImpact(
  amountIn: bigint,
  amountOut: bigint,
  marketPrice: number, // token1/token0
  decimals0: number,
  decimals1: number,
): number {
  const executionPrice =
    Number(amountOut) / 10 ** decimals1 / (Number(amountIn) / 10 ** decimals0);
  return Math.abs(1 - executionPrice / marketPrice);
}

Slippage Tolerance

• Stablecoin pairs: 0.01% - 0.05%
• Major pairs (ETH/USDC): 0.1% - 0.5%
• Volatile pairs: 0.5% - 1.0%
• Low liquidity: 1% - 5%

Calculate minimum amount out:

typescript

const minAmountOut = (amountOut * (10000n - BigInt(slippageBps))) / 10000n;

Multi-hop Routing

For tokens without direct pools, route through intermediary tokens:

typescript

// ETH -> USDC -> DAI (two hops)
const path = encodePacked(
  ["address", "uint24", "address", "uint24", "address"],
  [WETH, 3000, USDC, 100, DAI],
);

const quote = await client.readContract({
  address: quoterV2Address,
  abi: quoterV2Abi,
  functionName: "quoteExactInput",
  args: [path, amountIn],
});

Gas Estimation

Typical gas costs by swap complexity:

• Single hop: ~130,000 gas
• Two hops: ~200,000 gas
• Three hops: ~270,000 gas

Always add a 15-20% buffer to gas estimates.

MEV Considerations

When building swap tools:

• Recommend private RPCs (Flashbots Protect) for large swaps
• Warn users about sandwich attack risk for high-impact swaps
• Suggest using deadline parameters to limit exposure