Get Swap Quotes
Estimate fees and amounts with quoteSwap before executing a swap.
This guide shows how to quote before swapping and use quotes for fee estimation. Quotes use quoteSwap(), which works with read-only accounts as well as signing accounts.
Quote before swapping
You can preview fee and token amounts for the same parameters you would pass to swap() using quoteSwap():
const quote = await swapProtocol.quoteSwap({
tokenIn: '0xdAC17F958D2ee523a2206206994597C13D831ec7',
tokenOut: '0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2',
tokenInAmount: 1000000n
})
console.log('Estimated fee (account units):', quote.fee)
console.log('Tokens in (base units):', quote.tokenInAmount)
console.log('Tokens out (base units):', quote.tokenOutAmount)You can quote an exact-output style trade the same way by passing tokenOutAmount instead of tokenInAmount to quoteSwap():
const quote = await swapProtocol.quoteSwap({
tokenIn: '0xdAC17F958D2ee523a2206206994597C13D831ec7',
tokenOut: '0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2',
tokenOutAmount: 500000000000000000n
})
console.log('Estimated fee (account units):', quote.fee)
console.log('Required token in (base units):', quote.tokenInAmount)With an ERC‑4337 account, pass the optional second argument to preview the fee for a specific paymaster, sponsorship, or native-fee configuration:
const quote = await swapAA.quoteSwap({
tokenIn: '0xdAC17F958D2ee523a2206206994597C13D831ec7',
tokenOut: '0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2',
tokenInAmount: 1000000n
}, {
paymasterToken: {
address: '0xdAC17F958D2ee523a2206206994597C13D831ec7'
}
})Fee estimation
Read quote.fee in the account's fee units: native wei for a standard EVM account, token base units for token-paymaster fees, or zero for sponsorship. The quote excludes any separate input-token approval. quoteSwap() does not enforce swapMaxFee.
The following examples use a standard EVM account, so the cap is in wei:
const quote = await swapProtocol.quoteSwap({
tokenIn: '0xdAC17F958D2ee523a2206206994597C13D831ec7',
tokenOut: '0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2',
tokenInAmount: 1000000n
})
const maxFee = 200000000000000n
console.log('Quoted fee (wei):', quote.fee, 'cap:', maxFee)Compare the estimate with an exclusive cap and pass the same cap to swap(). Execution obtains a fresh fee quote and rejects a fee equal to or above swapMaxFee:
const maxFee = 200000000000000n
const quote = await swapProtocol.quoteSwap({
tokenIn: '0xdAC17F958D2ee523a2206206994597C13D831ec7',
tokenOut: '0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2',
tokenInAmount: 1000000n
})
if (quote.fee < maxFee) {
const result = await swapProtocol.swap({
tokenIn: '0xdAC17F958D2ee523a2206206994597C13D831ec7',
tokenOut: '0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2',
tokenInAmount: 1000000n
}, { swapMaxFee: maxFee })
console.log('Swap hash:', result.hash)
}On-chain conditions can change between quote and execution. The executed swap() may still differ slightly from the last quoteSwap() result.