Adjust slippage tolerance in Uniswap programatically

Question

I've been able to do swaps through Uniswap's peripheral smart contract Router 02 by calling any of the functions such as:

function swapTokensForExactTokens(
  uint amountOut,
  uint amountInMax,
  address[] calldata path,
  address to,
  uint deadline
) external returns (uint[] memory amounts);

However, none of these functions has any field referring to the slippage (amount the price moves in a trading pair between when a transaction is submitted and when it is executed), and I don't know exactly at which stage the slippage is set before launching the swap transaction.

Is there any way to handle the slippage tolerance programatically when executing a swap transaction?

Answer 1

Yes, you can adjust it with that function.

The Uniswap router swap functions trade asset A for asset B, with slippage. Mostly they are of type "give A, get B, while either the amount of A or B remains static". So you for example have a swap "I want to pay x amount of A tokens and get as many B tokens as possible" or "I want to pay as few A tokens as possible and get x amount of B tokens".

In your case you are using a function which gives a minimum amount of tokenA and gets a certain numbers of tokenB out. So the amountOut is a static number which you define, and amountInMax is the maximum you are willing to input tokens A to get the static amount of tokens B.

So your slippage is defined by amountInMax.

Answer 2

You need to set the slippage when you set the route:

The Route entity represents one or more ordered Uniswap pairs with a fully specified path from input token to output token.

after stuying uniswap-sdk-core-repo

 import JSBI from 'jsbi'
 import { CurrencyAmount, TradeType, Percent } from "@uniswap/sdk-core";
 import { AlphaRouter } from "@uniswap/smart-order-router";

 // goerli chainId=5
 const router = new AlphaRouter({ chainId: 5, provider: web3Provider });


// maximum percentage of slippage to fulfill the order
  const perSlippage = new Percent(slippageAmount, 100);
  const wei = ethers.utils.parseUnits(inputAmount.toString(), decimalsOfToken0);
  const currencyAmount = CurrencyAmount.fromRawAmount(token0, JSBI.BigInt(wei));

 //building the route
  const route = await router.route(currencyAmount, UNI, TradeType.EXACT_INPUT, {
    recipient: walletAddress,
    slippageTolerance: perSlippage,
    deadline: enterDeadline,
  });