swap

Swap Skill

Purpose

This skill enables Claude to help users swap tokens on decentralized exchanges across EVM-compatible networks.

Security Warnings

BEFORE ANY SWAP:

ALWAYS show the expected output amount and minimum received
ALWAYS explain slippage and its implications
ALWAYS check token approvals before swapping
WARN about potential price impact for large trades
RECOMMEND checking token contract legitimacy

Supported DEXs

DEX	Network	Router Address
PancakeSwap V2	BNB Chain	0x10ED43C718714eb63d5aA57B78B54704E256024E
PancakeSwap V3	BNB Chain	0x13f4EA83D0bd40E75C8222255bc855a974568Dd4
Uniswap V2	Ethereum	0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D
Uniswap V3	Ethereum	0xE592427A0AEce92De3Edee1F18E0157C05861564
QuickSwap	Polygon	0xa5E0829CaCEd8fFDD4De3c43696c57F7D7A678ff
SushiSwap	Multiple	Varies by network

Quick Start

Get Swap Quote (PancakeSwap V2)

import { createPublicClient, http, parseUnits, formatUnits } from 'viem'
import { bsc } from 'viem/chains'

const PANCAKE_ROUTER_ABI = [
  {
    name: 'getAmountsOut',
    type: 'function',
    inputs: [
      { name: 'amountIn', type: 'uint256' },
      { name: 'path', type: 'address[]' }
    ],
    outputs: [{ name: 'amounts', type: 'uint256[]' }]
  }
]

const publicClient = createPublicClient({
  chain: bsc,
  transport: http()
})

const PANCAKE_ROUTER = '0x10ED43C718714eb63d5aA57B78B54704E256024E'
const WBNB = '0xbb4CdB9CBd36B01bD1cBaEBF2De08d9173bc095c'
const USDT = '0x55d398326f99059fF775485246999027B3197955'

// Get quote: How much USDT for 1 BNB?
const amountIn = parseUnits('1', 18) // 1 BNB
const path = [WBNB, USDT] // Swap path

const amounts = await publicClient.readContract({
  address: PANCAKE_ROUTER,
  abi: PANCAKE_ROUTER_ABI,
  functionName: 'getAmountsOut',
  args: [amountIn, path]
})

console.log('Input:', formatUnits(amounts[0], 18), 'BNB')
console.log('Output:', formatUnits(amounts[1], 18), 'USDT')

Execute Swap (Exact Input)

import { createWalletClient, createPublicClient, http, parseUnits } from 'viem'
import { privateKeyToAccount } from 'viem/accounts'
import { bsc } from 'viem/chains'

const PANCAKE_ROUTER_ABI = [
  {
    name: 'swapExactTokensForTokens',
    type: 'function',
    inputs: [
      { name: 'amountIn', type: 'uint256' },
      { name: 'amountOutMin', type: 'uint256' },
      { name: 'path', type: 'address[]' },
      { name: 'to', type: 'address' },
      { name: 'deadline', type: 'uint256' }
    ],
    outputs: [{ name: 'amounts', type: 'uint256[]' }]
  },
  {
    name: 'swapExactETHForTokens',
    type: 'function',
    inputs: [
      { name: 'amountOutMin', type: 'uint256' },
      { name: 'path', type: 'address[]' },
      { name: 'to', type: 'address' },
      { name: 'deadline', type: 'uint256' }
    ],
    outputs: [{ name: 'amounts', type: 'uint256[]' }],
    stateMutability: 'payable'
  }
]

const account = privateKeyToAccount('0x...')
const PANCAKE_ROUTER = '0x10ED43C718714eb63d5aA57B78B54704E256024E'
const WBNB = '0xbb4CdB9CBd36B01bD1cBaEBF2De08d9173bc095c'
const USDT = '0x55d398326f99059fF775485246999027B3197955'

const walletClient = createWalletClient({
  account,
  chain: bsc,
  transport: http()
})

// Swap BNB for USDT
const amountIn = parseUnits('0.1', 18) // 0.1 BNB
const amountOutMin = parseUnits('50', 18) // Minimum 50 USDT (with slippage)
const path = [WBNB, USDT]
const deadline = BigInt(Math.floor(Date.now() / 1000) + 60 * 20) // 20 minutes

const hash = await walletClient.writeContract({
  address: PANCAKE_ROUTER,
  abi: PANCAKE_ROUTER_ABI,
  functionName: 'swapExactETHForTokens',
  args: [amountOutMin, path, account.address, deadline],
  value: amountIn
})

console.log('Swap transaction:', hash)

Common Operations

1. Approve Token for Swap

Before swapping ERC20 tokens, you must approve the router:

import { createWalletClient, http, maxUint256 } from 'viem'
import { privateKeyToAccount } from 'viem/accounts'
import { bsc } from 'viem/chains'

const ERC20_ABI = [
  {
    name: 'approve',
    type: 'function',
    inputs: [
      { name: 'spender', type: 'address' },
      { name: 'amount', type: 'uint256' }
    ],
    outputs: [{ name: '', type: 'bool' }]
  },
  {
    name: 'allowance',
    type: 'function',
    inputs: [
      { name: 'owner', type: 'address' },
      { name: 'spender', type: 'address' }
    ],
    outputs: [{ name: '', type: 'uint256' }]
  }
]

const account = privateKeyToAccount('0x...')
const tokenAddress = '0x...' // Token to swap FROM
const routerAddress = '0x10ED43C718714eb63d5aA57B78B54704E256024E'

const publicClient = createPublicClient({
  chain: bsc,
  transport: http()
})

const walletClient = createWalletClient({
  account,
  chain: bsc,
  transport: http()
})

// Check current allowance
const allowance = await publicClient.readContract({
  address: tokenAddress,
  abi: ERC20_ABI,
  functionName: 'allowance',
  args: [account.address, routerAddress]
})

// If allowance is 0, approve
if (allowance === 0n) {
  const hash = await walletClient.writeContract({
    address: tokenAddress,
    abi: ERC20_ABI,
    functionName: 'approve',
    args: [routerAddress, maxUint256]
  })
  console.log('Approval tx:', hash)
}

2. Calculate Slippage

// Calculate minimum output with slippage tolerance
function calculateMinOutput(
  expectedOutput: bigint,
  slippagePercent: number
): bigint {
  const slippageBps = BigInt(Math.floor(slippagePercent * 100)) // Convert to basis points
  const minOutput = expectedOutput - (expectedOutput * slippageBps / 10000n)
  return minOutput
}

// Example: 1% slippage on 100 USDT expected
const expected = parseUnits('100', 18)
const minOutput = calculateMinOutput(expected, 1) // 1% slippage
console.log('Min output:', formatUnits(minOutput, 18)) // 99 USDT

3. Multi-Hop Swap (Token A → Token B → Token C)

// Sometimes direct pair doesn't exist, need to route through intermediate token
const CAKE = '0x0E09FaBB73Bd3Ade0a17ECC321fD13a19e81cE82'
const WBNB = '0xbb4CdB9CBd36B01bD1cBaEBF2De08d9173bc095c'
const USDT = '0x55d398326f99059fF775485246999027B3197955'

// Swap CAKE → USDT via WBNB
const multiHopPath = [CAKE, WBNB, USDT]

const amounts = await publicClient.readContract({
  address: PANCAKE_ROUTER,
  abi: PANCAKE_ROUTER_ABI,
  functionName: 'getAmountsOut',
  args: [parseUnits('10', 18), multiHopPath]
})

console.log('CAKE in:', formatUnits(amounts[0], 18))
console.log('WBNB intermediate:', formatUnits(amounts[1], 18))
console.log('USDT out:', formatUnits(amounts[2], 18))

4. Check Token Price

// Get token price in terms of another token
async function getTokenPrice(
  publicClient: any,
  routerAddress: string,
  tokenA: string,
  tokenB: string,
  decimalsA: number,
  decimalsB: number
): Promise<string> {
  const ROUTER_ABI = [{
    name: 'getAmountsOut',
    type: 'function',
    inputs: [
      { name: 'amountIn', type: 'uint256' },
      { name: 'path', type: 'address[]' }
    ],
    outputs: [{ name: 'amounts', type: 'uint256[]' }]
  }]

  const amountIn = parseUnits('1', decimalsA)

  try {
    const amounts = await publicClient.readContract({
      address: routerAddress,
      abi: ROUTER_ABI,
      functionName: 'getAmountsOut',
      args: [amountIn, [tokenA, tokenB]]
    })
    return formatUnits(amounts[1], decimalsB)
  } catch {
    return 'No liquidity'
  }
}

// Example: Get BNB price in USDT
const price = await getTokenPrice(
  publicClient,
  PANCAKE_ROUTER,
  WBNB,
  USDT,
  18,
  18
)
console.log('1 BNB =', price, 'USDT')

Swap Workflow

When a user requests a swap, follow this workflow:

Step 1: Gather Information

Please provide:
1. Network (e.g., BNB Chain, Ethereum)
2. Token to swap FROM (name or address)
3. Token to swap TO (name or address)
4. Amount to swap
5. Slippage tolerance (default: 0.5%)

Step 2: Get Quote and Preview

🔄 Swap Preview
═══════════════════
Network: BNB Smart Chain
DEX: PancakeSwap V2

📥 Input:
   Token: BNB
   Amount: 1.0 BNB

📤 Output:
   Token: USDT
   Expected: 612.45 USDT
   Minimum (0.5% slippage): 609.38 USDT

💱 Rate: 1 BNB = 612.45 USDT
📊 Price Impact: 0.12%
⛽ Estimated Gas: ~0.001 BNB

⚠️ Slippage tolerance: 0.5%
   If price moves more than this, transaction will revert.

Proceed with swap? (yes/no)

Step 3: Check Approval (if needed)

🔐 Token Approval Required

The router needs permission to spend your BNB.
This is a one-time approval for this token.

Approve unlimited amount? (yes/no)
Or specify a specific amount:

Step 4: Execute and Confirm

✅ Swap Initiated!

Transaction Hash: 0x8a2f...b4c1
Status: Pending...

[Waiting for confirmation...]

✅ Swap Confirmed!
Block: 31234567
Input: 1.0 BNB
Output: 611.89 USDT
Gas Used: 152,000
Explorer: https://bscscan.com/tx/0x8a2f...b4c1

Slippage Guide

Slippage	Use Case
0.1-0.5%	Stable pairs (USDT/USDC), high liquidity
0.5-1%	Major tokens (BNB, ETH), normal market
1-3%	Smaller tokens, moderate volatility
3-5%	Low liquidity tokens, high volatility
5%+	Meme coins, very low liquidity (risky!)

Error Handling

Common Errors

Error	Cause	Solution
INSUFFICIENT_OUTPUT_AMOUNT	Price moved beyond slippage	Increase slippage or retry
TRANSFER_FAILED	Token transfer issue	Check approval, balance
EXPIRED	Transaction took too long	Retry with new deadline
K	Constant product invariant	Liquidity issue, try smaller amount

Example Error Handling

try {
  const hash = await walletClient.writeContract({
    address: PANCAKE_ROUTER,
    abi: PANCAKE_ROUTER_ABI,
    functionName: 'swapExactETHForTokens',
    args: [amountOutMin, path, account.address, deadline],
    value: amountIn
  })
  console.log('Swap successful:', hash)
} catch (error) {
  if (error.message.includes('INSUFFICIENT_OUTPUT_AMOUNT')) {
    console.log('Error: Price changed too much!')
    console.log('Solutions:')
    console.log('1. Increase slippage tolerance')
    console.log('2. Wait and try again')
    console.log('3. Reduce swap amount')
  } else if (error.message.includes('EXPIRED')) {
    console.log('Error: Transaction expired')
    console.log('Please try again with a fresh quote')
  } else {
    console.log('Swap failed:', error.message)
  }
}

Popular Token Pairs

BNB Smart Chain

BNB/USDT
BNB/BUSD
CAKE/BNB
ETH/BNB

Ethereum

ETH/USDC
ETH/USDT
WBTC/ETH
UNI/ETH

Best Practices

Always get fresh quotes - Prices change rapidly
Start with small amounts - Test the swap works
Use appropriate slippage - Too low fails, too high loses money
Check price impact - Large swaps can move the market
Verify token contracts - Avoid scam tokens
Consider timing - Gas fees vary, wait for lower fees

About this skill