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Uniswap: Swap Tokens

The Simple Way
var uniswap = web3.UniswapV4();
var quote = await uniswap.Pricing.Quoter.QuoteExactInputQueryAsync(quoteParams);
var receipt = await uniswap.UniversalRouter.ExecuteRequestAndWaitForReceiptAsync(executeFunction);

Access Uniswap through web3.UniswapV4() — pool discovery, quoting, and routing are all built in.

Swapping tokens on Uniswap is the most common DeFi operation. Nethereum provides a complete Uniswap integration covering V2, V3, and V4 — including price quoting, slippage protection, and the Universal Router for executing swaps on-chain. This guide walks through the V4 flow (the latest and recommended version), with V3 and V2 patterns at the end.

dotnet add package Nethereum.Uniswap

Connect to Uniswap V4​

The UniswapV4() extension method on Web3 gives you access to the entire Uniswap V4 service hierarchy — pools, pricing, positions, and routing. It defaults to Mainnet addresses, but you can pass addresses for any supported network:

using Nethereum.Web3;
using Nethereum.Web3.Accounts;
using Nethereum.Uniswap.V4;

var web3 = new Web3(new Account("0xYOUR_PRIVATE_KEY"), "https://base-sepolia.drpc.org");

// Defaults to Mainnet contract addresses
var uniswap = web3.UniswapV4();

// Or specify a different network
var uniswap = web3.UniswapV4(UniswapV4Addresses.BaseSepolia);

The uniswap object exposes sub-services: uniswap.Pools for pool state, uniswap.Pricing for quotes and price calculations, uniswap.Positions for liquidity management, and uniswap.UniversalRouter for executing swaps.

Define a Pool​

A Uniswap V4 pool is identified by a PoolKey — the two currencies, fee tier, tick spacing, and an optional hooks contract. You need to know the pool you want to trade in:

using Nethereum.Uniswap.V4.Contracts.PoolManager.ContractDefinition;
using Nethereum.Util;

var eth = AddressUtil.ZERO_ADDRESS;  // Native ETH uses the zero address
var usdc = "0x91D1e0b9f6975655A381c79fd6f1D118D1c5b958";

var pool = new PoolKey
{
    Currency0 = eth,
    Currency1 = usdc,
    Fee = 500,           // 0.05% fee tier
    TickSpacing = 10,
    Hooks = AddressUtil.ZERO_ADDRESS  // No hooks
};

The Currency0 must be the lower address (sorted). Native ETH is always address(0), which sorts first. If you're not sure which pool exists for a pair, see the Pool Discovery section below.

Quote a Price​

Before swapping, get a quote to see how much output you'll receive. The quoter simulates the swap on-chain without executing it — no gas cost, no state change:

var v4Quoter = uniswap.Pricing.Quoter;

var pathKeys = V4PathEncoder.EncodeMultihopExactInPath(
    new List<PoolKey> { pool }, eth);

var amountIn = Web3.Convert.ToWei(0.001);

var quoteParams = new QuoteExactParams
{
    Path = pathKeys,
    ExactAmount = amountIn,
    ExactCurrency = eth
};

var quote = await v4Quoter.QuoteExactInputQueryAsync(quoteParams);
var quoteAmount = Web3.Convert.FromWei(quote.AmountOut, 6); // USDC has 6 decimals
Console.WriteLine($"0.001 ETH = {quoteAmount} USDC");

The V4PathEncoder handles encoding the swap path. For a single-hop swap (one pool), pass a list with one pool key. For multi-hop swaps, pass multiple pool keys — the router will execute them in sequence.

Execute the Swap​

Swaps go through the Universal Router, which batches multiple actions (swap, settle input, take output) into a single transaction. You build the actions with the V4 actions builder:

var universalRouter = uniswap.UniversalRouter;
var v4ActionBuilder = uniswap.GetUniversalRouterV4ActionsBuilder();

// 1. Add the swap action
v4ActionBuilder.AddCommand(new SwapExactIn
{
    CurrencyIn = eth,
    AmountIn = amountIn,
    AmountOutMinimum = quote.AmountOut * 95 / 100, // 5% slippage tolerance
    Path = pathKeys.MapToActionV4()
});

// 2. Settle the input currency (send ETH to the router)
v4ActionBuilder.AddCommand(new SettleAll
{
    Currency = eth,
    Amount = amountIn
});

// 3. Take the output currency (receive USDC)
v4ActionBuilder.AddCommand(new TakeAll
{
    Currency = usdc,
    MinAmount = 0
});

// Build and execute
var routerBuilder = new UniversalRouterBuilder();
routerBuilder.AddCommand(v4ActionBuilder.GetV4SwapCommand());

var executeFunction = routerBuilder.GetExecuteFunction(amountIn);
var receipt = await universalRouter.ExecuteRequestAndWaitForReceiptAsync(executeFunction);
Console.WriteLine($"Swap tx: {receipt.TransactionHash}");

The three actions form the standard swap pattern: swap (exchange tokens in the pool), settle (pay the input), take (collect the output). The AmountOutMinimum on the swap protects you from getting less than expected due to price movement — this is your slippage tolerance.

Slippage and Price Impact​

Slippage protection is critical in DeFi. Nethereum provides calculators for both slippage bounds and price impact monitoring:

var slippage = uniswap.Pricing.SlippageCalculator;

// For exact-input swaps: calculate the minimum acceptable output
var tolerance = new BigDecimal(0.5m); // 0.5% slippage
var minAmountOut = slippage.CalculateMinimumAmountOut(expectedAmountOut, tolerance);

// For exact-output swaps: calculate the maximum you're willing to pay
var maxAmountIn = slippage.CalculateMaximumAmountIn(expectedAmountIn, tolerance);

Price impact tells you how much your trade moves the pool price. Large trades in shallow pools can have significant impact:

var impactCalc = uniswap.Pricing.PriceImpactCalculator;

var priceImpact = impactCalc.CalculatePriceImpact(inputAmount, outputAmount, midPrice);
var level = impactCalc.ClassifyPriceImpact(priceImpact);
// Returns: Low (<1%), Medium (1-3%), High (3-5%), Critical (>5%)

var warning = impactCalc.GetPriceImpactWarning(level);

A swap with >5% price impact usually means you're trading too large for that pool's liquidity. Consider splitting the trade or finding a deeper pool.

Price Calculations​

You can calculate human-readable prices from the pool's raw sqrtPriceX96 value:

// Get the price of token0 in terms of token1 (adjusted for decimals)
var priceToken0InToken1 = uniswap.Pricing.PriceCalculator.CalculatePriceFromSqrtPriceX96(
    sqrtPriceX96,
    decimals0: 18,
    decimals1: 6);

// Inverse gives token1 price in terms of token0
var priceToken1InToken0 = priceToken0InToken1 == 0 ? 0 : 1 / priceToken0InToken1;
// e.g., priceToken0InToken1 = 3500 (1 ETH = 3500 USDC)

Tick math conversions are also available for working with price ranges:

var sqrtPriceX96 = uniswap.Math.Tick.GetSqrtRatioAtTick(tick);
var tick = uniswap.Math.Tick.GetTickAtSqrtRatio(sqrtPriceX96);

Discover Pools​

If you don't know which pools exist for a token pair, the pool cache can discover them from on-chain Initialize events:

var poolCache = uniswap.Pools.Cache;
var latestBlock = await web3.Eth.Blocks.GetBlockNumber.SendRequestAsync();
var startBlock = latestBlock.Value - 100_000;

var pools = await poolCache.FindPoolsForTokenAsync(
    token: usdc,
    fromBlockNumber: startBlock,
    toBlockNumber: latestBlock.Value);

foreach (var p in pools)
{
    Console.WriteLine($"Pool: {p.Currency0}/{p.Currency1}, Fee: {p.Fee}");
}

Discovered pools are automatically cached. You can also fetch and cache a specific pool directly:

var pool = await poolCache.GetOrFetchPoolAsync(
    currency0: eth, currency1: usdc, fee: 500, tickSpacing: 10);

Console.WriteLine($"Exists: {pool.Exists}, Tick: {pool.Tick}");

Find the Best Swap Path​

For large trades or exotic pairs, routing through an intermediate token (like WETH or DAI) can give better prices. The path finder evaluates all cached pools:

var pathFinder = uniswap.Pricing.QuotePricePathFinder;
var cachedPools = await poolCache.GetAllCachedPoolsAsync();

// Direct path only
var bestDirect = await pathFinder.FindBestDirectPathAsync(
    tokenIn: eth, tokenOut: usdc,
    amountIn: Web3.Convert.ToWei(1),
    candidatePools: cachedPools);

// Multi-hop through intermediate tokens
var bestPath = await pathFinder.FindBestPathAsync(
    tokenIn: usdc, tokenOut: weth,
    amountIn: Web3.Convert.ToWei(1000, UnitConversion.EthUnit.Mwei),
    intermediateTokens: new[] { dai, eth },
    candidatePools: cachedPools);

Console.WriteLine($"Best output: {Web3.Convert.FromWei(bestPath.AmountOut, 18)} WETH");
Console.WriteLine($"Hops: {bestPath.Path.Count}");

Token Approvals​

Before swapping ERC-20 tokens (not native ETH), the router needs approval to spend them. Nethereum's approval service handles checking and approving in one call:

await uniswap.Accounts.Approvals.CheckAndApproveIfNeededAsync(
    tokenAddress, owner, spender, requiredAmount);

You can also check approval status separately:

var status = await uniswap.Accounts.Approvals.CheckApprovalAsync(
    tokenAddress, owner, spender, requiredAmount);

if (!status.IsApproved)
{
    await uniswap.Accounts.Approvals.ApproveAsync(
        tokenAddress, spender, AccountApprovalService.GetMaxApprovalAmount());
}

Validate Balances​

Before executing a swap, verify the sender has enough tokens:

var balanceResult = await uniswap.Accounts.Balances.ValidateBalanceAsync(
    tokenAddress, owner, requiredAmount);

if (!balanceResult.HasSufficientBalance)
{
    Console.WriteLine($"Need {balanceResult.Deficit} more tokens");
}

V3 Swaps with Permit2​

For Uniswap V3, swaps use the same Universal Router but with Permit2 for gasless approvals. The flow is: approve Permit2 once, then sign off-chain permits for each swap:

// One-time: approve Permit2 to spend your WETH
var weth9Service = web3.Eth.ERC20.GetContractService(weth9);
await weth9Service.ApproveRequestAndWaitForReceiptAsync(permit2Address, IntType.MAX_INT256_VALUE);

// Per-swap: sign a Permit2 authorization
var permit = new PermitSingle
{
    Spender = universalRouterAddress,
    SigDeadline = 2000000000,
    Details = new PermitDetails
    {
        Amount = amountIn * 100000,
        Expiration = 0,
        Nonce = 0,
        Token = weth9
    }
};

var permitService = new Permit2Service(web3, permit2Address);
var signedPermit = await permitService.GetSinglePermitWithSignatureAsync(
    permit, new EthECKey(privateKey));

// Build the swap via Universal Router
var planner = new UniversalRouterBuilder();
planner.AddCommand(new Permit2PermitCommand
{
    Permit = signedPermit.PermitRequest,
    Signature = signedPermit.GetSignatureBytes()
});
planner.AddCommand(new V3SwapExactInCommand
{
    AmountIn = amountIn,
    AmountOutMinimum = quote.AmountOut - 10000,
    Path = path,
    Recipient = account.Address,
    FundsFromPermit2OrUniversalRouter = true
});

var receipt = await universalRouterService.ExecuteRequestAndWaitForReceiptAsync(
    planner.GetExecuteFunction(amountIn));

Error Handling​

Uniswap reverts with custom errors. The Universal Router service can decode them:

try
{
    var receipt = await universalRouter.ExecuteRequestAndWaitForReceiptAsync(executeFunction);
}
catch (SmartContractCustomErrorRevertException e)
{
    var error = universalRouterService.FindCustomErrorException(e);
    if (error != null)
    {
        Console.WriteLine($"Uniswap error: {error.Message}");
    }
}

Common errors: InsufficientOutputAmount (slippage too tight), InvalidPool (pool doesn't exist), Expired (deadline passed).

Next Steps​