Swap Integration

Swap Integration

Integrate Uniswap swaps into frontends, backends, and smart contracts.

Prerequisites

This skill assumes familiarity with viem basics (client setup, account management, contract interactions, transaction signing). Install the uniswap-viem plugin for comprehensive viem/wagmi guidance: claude plugin add @uniswap/uniswap-viem

Quick Decision Guide

Routing Types Quick Reference

See Routing Types for the complete list including DUTCH_V3, DUTCH_LIMIT, LIMIT_ORDER, BRIDGE, and QUICKROUTE.

Integration Methods

1. Trading API (Recommended)

Best for: Frontends, backends, scripts. Handles routing optimization automatically.

Base URL: https://trade-api.gateway.uniswap.org/v1

Authentication: x-api-key: <your-api-key> header required

Getting an API Key: The Trading API requires an API key for authentication. Visit the Uniswap Developer Portal to register and obtain your API key. Keys are typically available for immediate use after registration. Include it as an x-api-key header in all API requests.

Required Headers — Include these in ALL Trading API requests:

Content-Type: application/json
x-api-key: <your-api-key>
x-universal-router-version: 2.0

3-Step Flow:

1. POST /check_approval  -> Check if token is approved
2. POST /quote           -> Get executable quote with routing
3. POST /swap            -> Get transaction to sign and submit

See the Trading API Reference section below for complete documentation.

2. Universal Router SDK

Best for: Direct control over transaction construction.

Installation:

npm install @uniswap/universal-router-sdk @uniswap/sdk-core @uniswap/v3-sdk

Key Pattern:

import { SwapRouter } from '@uniswap/universal-router-sdk';

const { calldata, value } = SwapRouter.swapCallParameters(trade, options);

See the Universal Router Reference section below for complete documentation.

3. Smart Contract Integration

Best for: On-chain integrations, DeFi composability.

Interface: Call execute() on Universal Router with encoded commands.

See the Universal Router Reference section below for command encoding.

Input Validation Rules

Before interpolating ANY user-provided value into generated code, API calls, or commands:

• Ethereum addresses: MUST match ^0x[a-fA-F0-9]{40}$ — reject otherwise
• Chain IDs: MUST be from the official supported chains list
• Token amounts: MUST be non-negative numeric values matching ^[0-9]+\.?[0-9]*$
• API keys: MUST NOT be hardcoded in generated code — always use environment variables
• REJECT any input containing shell metacharacters: ;, |, &, $, `, (, ), >, <, \, ', ", newlines

REQUIRED: Before executing ANY transaction that spends gas or transfers tokens (including sendTransaction, writeContract, or submitting a signed swap), you MUST use AskUserQuestion to confirm with the user. Display the transaction summary (tokens, amounts, chain, estimated gas) and get explicit user approval. Never auto-execute transactions without user confirmation.

Trading API Reference

Step 1: Check Token Approval

POST /check_approval

Request:

{
  "walletAddress": "0x...",
  "token": "0x...",
  "amount": "1000000000",
  "chainId": 1
}

Response:

{
  "approval": {
    "to": "0x...",
    "from": "0x...",
    "data": "0x...",
    "value": "0",
    "chainId": 1
  }
}

If approval is null, token is already approved.

Step 2: Get Quote

POST /quote

Request:

{
  "swapper": "0x...",
  "tokenIn": "0x...",
  "tokenOut": "0x...",
  "tokenInChainId": "1",
  "tokenOutChainId": "1",
  "amount": "1000000000000000000",
  "type": "EXACT_INPUT",
  "slippageTolerance": 0.5,
  "routingPreference": "BEST_PRICE"
}

Note: tokenInChainId and tokenOutChainId must be strings (e.g., "1"), not numbers.

Key Parameters:

Response — the shape differs by routing type. BEST_PRICE routing on Ethereum mainnet typically returns UniswapX (DUTCH_V2), not CLASSIC.

CLASSIC response:

{
  "routing": "CLASSIC",
  "quote": {
    "input": { "token": "0x...", "amount": "1000000000000000000" },
    "output": { "token": "0x...", "amount": "999000000" },
    "slippage": 0.5,
    "route": [],
    "gasFee": "5000000000000000",
    "gasFeeUSD": "0.01",
    "gasUseEstimate": "150000"
  },
  "permitData": null
}

UniswapX (DUTCH_V2/V3/PRIORITY) response — different quote shape, no quote.output:

{
  "routing": "DUTCH_V2",
  "quote": {
    "orderInfo": {
      "reactor": "0x...",
      "swapper": "0x...",
      "nonce": "...",
      "deadline": 1772031054,
      "cosigner": "0x...",
      "input": {
        "token": "0x...",
        "startAmount": "1000000000000000000",
        "endAmount": "1000000000000000000"
      },
      "outputs": [
        {
          "token": "0x...",
          "startAmount": "999000000",
          "endAmount": "994000000",
          "recipient": "0x..."
        }
      ],
      "chainId": 1
    },
    "encodedOrder": "0x...",
    "orderHash": "0x..."
  },
  "permitData": { "domain": {}, "types": {}, "values": {} }
}

UniswapX output amount: Use quote.orderInfo.outputs[0].startAmount for the best-case fill amount. The endAmount is the floor after full auction decay. There is no quote.output.amount on UniswapX responses — accessing it will throw at runtime.

Display tip: For CLASSIC routes, use gasFeeUSD (a string with the USD value) for gas cost display. Do not manually convert gasFee (wei) using a hardcoded ETH price — this leads to wildly inaccurate estimates (e.g., ~$87 instead of ~$0.01). UniswapX routes are gasless for the swapper.

See QuoteResponse TypeScript Types for compile-time type safety across routing types.

Step 3: Execute Swap

POST /swap

Request - Spread the quote response directly into the body:

// CORRECT: Spread the quote response, strip null fields
const quoteResponse = await fetchQuote(params);

// Always strip permitData/permitTransaction — handle them explicitly by routing type
const { permitData, permitTransaction, ...cleanQuote } = quoteResponse;
const swapRequest: Record<string, unknown> = { ...cleanQuote };

const isUniswapX =
  quoteResponse.routing === 'DUTCH_V2' ||
  quoteResponse.routing === 'DUTCH_V3' ||
  quoteResponse.routing === 'PRIORITY';

if (isUniswapX) {
  // UniswapX: signature only — permitData must NOT go to /swap
  if (permit2Signature) swapRequest.signature = permit2Signature;
} else {
  // CLASSIC: both signature and permitData, or neither
  if (permit2Signature && permitData && typeof permitData === 'object') {
    swapRequest.signature = permit2Signature;
    swapRequest.permitData = permitData;
  }
}

Critical: Do NOT wrap the quote in {quote: quoteResponse}. The API expects the quote response fields spread into the request body.

Permit2 Rules (CLASSIC routes):

• signature and permitData must BOTH be present, or BOTH be absent
• Never set permitData: null — omit the field entirely
• The quote response often includes permitData: null — strip this before sending

UniswapX Routes (DUTCH_V2/V3/PRIORITY): permitData is used locally to sign the order but must be excluded from the /swap body. See Signing vs. Submission Flow.

Response (ready-to-sign transaction):

{
  "swap": {
    "to": "0x...",
    "from": "0x...",
    "data": "0x...",
    "value": "0",
    "chainId": 1,
    "gasLimit": "250000"
  }
}

Response Validation - Always validate before broadcasting:

function validateSwapResponse(response: SwapResponse): void {
  if (!response.swap?.data || response.swap.data === '' || response.swap.data === '0x') {
    throw new Error('swap.data is empty - quote may have expired');
  }
  if (!isAddress(response.swap.to) || !isAddress(response.swap.from)) {
    throw new Error('Invalid address in swap response');
  }
}

Supported Chains

See the official supported chains list for the current set of chains and their IDs.

Routing Types

UniswapX availability: UniswapX V2 orders are supported on Ethereum (1), Arbitrum (42161), Base (8453), and Unichain (130). The auction mechanism varies by chain — see UniswapX Auction Types below.

Critical Implementation Notes

These are common pitfalls discovered during real-world Trading API integration. Follow these rules to avoid on-chain reverts and API errors.

1. Swap Request Body Format

The /swap endpoint expects the quote response spread into the request body, not wrapped in a quote field.

// WRONG - causes "quote does not match any of the allowed types"
const badRequest = {
  quote: quoteResponse, // Don't wrap!
  signature: '0x...',
};

// CORRECT - spread the quote response
const goodRequest = {
  ...quoteResponse,
  signature: '0x...', // Only if using Permit2
};

2. Null Field Handling

The API rejects permitData: null. Additionally, permitData handling differs by routing type — see Signing vs. Submission Flow for the full explanation.

function prepareSwapRequest(quoteResponse: QuoteResponse, signature?: string): object {
  // Always strip permitData and permitTransaction from the spread — handle them explicitly
  const { permitData, permitTransaction, ...cleanQuote } = quoteResponse;
  const request: Record<string, unknown> = { ...cleanQuote };

  // UniswapX (DUTCH_V2, DUTCH_V3, PRIORITY): permitData is for LOCAL signing only.
  // The /swap body must NOT include permitData — the order is encoded in
  // quote.encodedOrder. Only the signature is needed.
  const isUniswapX =
    quoteResponse.routing === 'DUTCH_V2' ||
    quoteResponse.routing === 'DUTCH_V3' ||
    quoteResponse.routing === 'PRIORITY';

  if (isUniswapX) {
    if (signature) request.signature = signature;
  } else {
    // CLASSIC: both signature and permitData required together, or both omitted.
    // The Universal Router contract needs permitData to verify the Permit2
    // authorization on-chain.
    if (signature && permitData && typeof permitData === 'object') {
      request.signature = signature;
      request.permitData = permitData;
    }
  }

  return request;
}

3. Permit2 Field Rules

The rules for signature and permitData in the /swap request body depend on the routing type:

CLASSIC routes:

UniswapX routes (DUTCH_V2/V3/PRIORITY):

4. Pre-Broadcast Validation

Always validate the swap response before sending to the blockchain:

import { isAddress, isHex } from 'viem';

function validateSwapBeforeBroadcast(swap: SwapTransaction): void {
  // 1. data must be non-empty hex
  if (!swap.data || swap.data === '' || swap.data === '0x') {
    throw new Error('swap.data is empty - this will revert on-chain. Re-fetch the quote.');
  }

  if (!isHex(swap.data)) {
    throw new Error('swap.data is not valid hex');
  }

  // 2. Addresses must be valid
  if (!isAddress(swap.to)) {
    throw new Error('swap.to is not a valid address');
  }

  if (!isAddress(swap.from)) {
    throw new Error('swap.from is not a valid address');
  }

  // 3. Value must be present (can be "0" for non-ETH swaps)
  if (swap.value === undefined || swap.value === null) {
    throw new Error('swap.value is missing');
  }
}

5. Browser Environment Setup

When using viem/wagmi in browser environments, you need Node.js polyfills:

Install buffer polyfill:

npm install buffer

Add to your entry file (before other imports):

// src/main.tsx or src/index.tsx
import { Buffer } from 'buffer';
globalThis.Buffer = Buffer;

// Then your other imports
import React from 'react';
import { WagmiProvider } from 'wagmi';
// ...

Vite configuration (vite.config.ts):

export default defineConfig({
  define: {
    global: 'globalThis',
  },
  optimizeDeps: {
    include: ['buffer'],
  },
  resolve: {
    alias: {
      buffer: 'buffer',
    },
  },
});

Without this setup, you'll see: ReferenceError: Buffer is not defined

CORS Proxy Configuration

The Trading API does not support browser CORS preflight requests — OPTIONS requests return 415 Unsupported Media Type. Direct fetch() calls from a browser will always fail. You must proxy API requests through your own server or dev server.

Vite dev proxy (merge into the same vite.config.ts used for the Buffer polyfill above):

export default defineConfig({
  server: {
    proxy: {
      '/api/uniswap': {
        target: 'https://trade-api.gateway.uniswap.org/v1',
        changeOrigin: true,
        rewrite: (path) => path.replace(/^\/api\/uniswap/, ''),
      },
    },
  },
});

Then use /api/uniswap/quote instead of the full URL in your frontend code.

Vercel production proxy (vercel.json):

{
  "rewrites": [
    {
      "source": "/api/uniswap/:path*",
      "destination": "https://trade-api.gateway.uniswap.org/v1/:path*"
    }
  ]
}

Cloudflare Pages (public/_redirects):

/api/uniswap/* https://trade-api.gateway.uniswap.org/v1/:splat 200

Next.js (next.config.js):

module.exports = {
  async rewrites() {
    return [
      {
        source: '/api/uniswap/:path*',
        destination: 'https://trade-api.gateway.uniswap.org/v1/:path*',
      },
    ];
  },
};

Without a proxy, you'll see: 415 Unsupported Media Type on preflight or CORS errors in the browser console.

6. Quote Freshness

• Quotes expire quickly (typically 30 seconds)
• Always re-fetch if the user takes time to review
• Use the deadline parameter to prevent stale execution
• If /swap returns empty data, the quote likely expired

7. QuoteResponse TypeScript Types

The quote response shape differs by routing type. Use a discriminated union on the routing field to get compile-time safety instead of casting to any:

type ClassicQuoteResponse = {
  routing: 'CLASSIC' | 'WRAP' | 'UNWRAP';
  quote: {
    input: { token: string; amount: string };
    output: { token: string; amount: string };
    slippage: number;
    route: unknown[];
    gasFee: string;
    gasFeeUSD: string;
    gasUseEstimate: string;
  };
  permitData: Record<string, unknown> | null;
};

type DutchOrderOutput = {
  token: string;
  startAmount: string;
  endAmount: string;
  recipient: string;
};

type UniswapXQuoteResponse = {
  routing: 'DUTCH_V2' | 'DUTCH_V3' | 'PRIORITY';
  quote: {
    orderInfo: {
      outputs: DutchOrderOutput[];
      input: { token: string; startAmount: string; endAmount: string };
      deadline: number;
      nonce: string;
    };
    encodedOrder: string;
    orderHash: string;
  };
  // EIP-712 typed data — sign locally, do NOT send to /swap
  permitData: Record<string, unknown> | null;
};

type QuoteResponse = ClassicQuoteResponse | UniswapXQuoteResponse;

// Type guard for routing-aware logic
function isUniswapXQuote(q: QuoteResponse): q is UniswapXQuoteResponse {
  return q.routing === 'DUTCH_V2' || q.routing === 'DUTCH_V3' || q.routing === 'PRIORITY';
}

// Reading the output amount by routing type
function getOutputAmount(q: QuoteResponse): string {
  if (isUniswapXQuote(q)) {
    const firstOutput = q.quote.orderInfo.outputs[0];
    if (!firstOutput) throw new Error('UniswapX quote has no outputs');
    // startAmount = best-case fill; endAmount = floor after auction decay
    return firstOutput.startAmount;
  }
  return q.quote.output.amount;
}

Universal Router Reference

The Universal Router is a unified interface for swapping across Uniswap v2, v3, and v4.

Core Function

function execute(
    bytes calldata commands,
    bytes[] calldata inputs,
    uint256 deadline
) external payable;

Command Encoding

Each command is a single byte:

Swap Commands

Token Operations

Permit2 Commands

SDK Usage

import { SwapRouter, UniswapTrade } from '@uniswap/universal-router-sdk'
import { TradeType } from '@uniswap/sdk-core'

// Build trade using v3-sdk or router-sdk
const trade = new RouterTrade({
  v3Routes: [...],
  tradeType: TradeType.EXACT_INPUT
})

// Get calldata for Universal Router
const { calldata, value } = SwapRouter.swapCallParameters(trade, {
  slippageTolerance: new Percent(50, 10000), // 0.5%
  recipient: walletAddress,
  deadline: Math.floor(Date.now() / 1000) + 1200 // 20 min
})

// Send transaction
const tx = await wallet.sendTransaction({
  to: UNIVERSAL_ROUTER_ADDRESS,
  data: calldata,
  value
})

Permit2 Integration

Permit2 enables signature-based token approvals instead of on-chain approve() calls.

Approval Target: Permit2 vs Legacy (Direct to Router)

There are two approval paths. Choose based on your integration type:

Permit2 flow (frontend with user signing):

1. User approves token to Permit2 contract (one-time)
2. Each swap: user signs an EIP-712 permit message
3. Universal Router uses the signature to transfer tokens via Permit2

Legacy flow (backend services, ERC-4337 smart accounts):

1. Approve token directly to the Universal Router address (one-time)
2. Each swap: no additional authorization needed
3. Simpler for automated systems that cannot sign EIP-712 messages

Use the Trading API's /check_approval endpoint — it returns the correct approval target based on the routing type.

How It Works

1. User approves Permit2 contract once (infinite approval)
2. For each swap, user signs a message authorizing the transfer
3. Universal Router uses signature to transfer tokens via Permit2

Two Modes

Integration Pattern

import { getContract, maxUint256, type Address } from 'viem';

const PERMIT2_ADDRESS = '0x000000000022D473030F116dDEE9F6B43aC78BA3' as const;

// Check if Permit2 approval exists
const allowance = await publicClient.readContract({
  address: PERMIT2_ADDRESS,
  abi: permit2Abi,
  functionName: 'allowance',
  args: [userAddress, tokenAddress, spenderAddress],
});

// If not approved, user must approve Permit2 first
if (allowance.amount < requiredAmount) {
  const hash = await walletClient.writeContract({
    address: tokenAddress,
    abi: erc20Abi,
    functionName: 'approve',
    args: [PERMIT2_ADDRESS, maxUint256],
  });
  await publicClient.waitForTransactionReceipt({ hash });
}

// Then sign permit for the swap
const permitSignature = await signPermit(...);

UniswapX Auction Types

UniswapX routes swaps through off-chain fillers who compete to execute orders at better prices than on-chain AMMs. The auction mechanism varies by chain.

Exclusive Dutch Auction (Ethereum)

• Starts with an RFQ (Request for Quote) phase where permissioned quoters compete
• Winning quoter receives exclusive filling rights for a set period
• If the exclusive filler doesn't execute, falls back to an open Dutch auction where the price decays each block
• Best for large swaps where MEV protection matters most

Trading API routing type: DUTCH_V2 or DUTCH_V3

Open Dutch Auction (Arbitrum)

• Direct open auction without an RFQ phase
• Fillers compete on-chain through a descending price mechanism
• Leverages Arbitrum's fast 0.25-second block times for rapid price discovery
• The Unimind algorithm sets auction parameters based on historical pair performance

Trading API routing type: DUTCH_V2

Priority Gas Auction (Base, Unichain)

• Fillers bid by submitting transactions with varying priority fees at a target block
• Highest priority fee wins the right to fill the order
• Exploits OP Stack's priority ordering mechanism
• Effective on chains where block builders respect priority ordering

Trading API routing type: PRIORITY

Key Properties (All Auction Types)

• Gasless for users — fillers pay gas fees, incorporated into final pricing
• No cost on failure — if a swap doesn't fill, the user pays nothing
• MEV protection — auction mechanics prevent frontrunning and sandwich attacks
• UniswapX V2 is currently supported on Ethereum (1), Arbitrum (42161), Base (8453), and Unichain (130)

For more detail, see the UniswapX Auction Types documentation.

UniswapX: Signing vs. Submission Flow

The permitData field in the quote response serves different purposes depending on the routing type. Conflating the two causes RequestValidationError on /swap.

CLASSIC flow — permitData goes to the server:

1. /quote returns permitData (EIP-712 typed data for the Permit2 allowance)
2. User signs permitData locally → produces signature
3. /swap body includes both signature and permitData — the Universal Router contract needs permitData to reconstruct and verify the Permit2 authorization on-chain

UniswapX flow (DUTCH_V2/V3/PRIORITY) — permitData stays local:

1. /quote returns permitData (EIP-712 typed data for the Dutch order)
2. User signs permitData locally → produces signature
3. /swap body includes only signature — the order is already fully encoded in quote.encodedOrder, which the off-chain filler system reads directly. Sending permitData to /swap causes a schema validation error.

Common mistake: The API error "quote" does not match any of the allowed types often points at the quote field, but the actual cause is permitData being present for a UniswapX route. Strip permitData before submitting — see the routing-aware prepareSwapRequest in Null Field Handling.

Direct Universal Router Integration (SDK)

For direct Universal Router integration without the Trading API, use the SDK's high-level API.

Installation

npm install @uniswap/universal-router-sdk @uniswap/router-sdk @uniswap/sdk-core @uniswap/v3-sdk viem

High-Level Approach (Recommended)

Use RouterTrade + SwapRouter.swapCallParameters() for automatic command building:

import { SwapRouter } from '@uniswap/universal-router-sdk';
import { Trade as RouterTrade } from '@uniswap/router-sdk';
import { TradeType, Percent } from '@uniswap/sdk-core';
import { Route as V3Route, Pool } from '@uniswap/v3-sdk';

// 1. Fetch pool data (required to construct routes)
// Using viem to read on-chain pool state:
const slot0 = await publicClient.readContract({
  address: poolAddress,
  abi: [
    {
      name: 'slot0',
      type: 'function',
      stateMutability: 'view',
      inputs: [],
      outputs: [
        { name: 'sqrtPriceX96', type: 'uint160' },
        { name: 'tick', type: 'int24' },
        { name: 'observationIndex', type: 'uint16' },
        { name: 'observationCardinality', type: 'uint16' },
        { name: 'observationCardinalityNext', type: 'uint16' },
        { name: 'feeProtocol', type: 'uint8' },
        { name: 'unlocked', type: 'bool' },
      ],
    },
  ],
  functionName: 'slot0',
});
const liquidity = await publicClient.readContract({
  address: poolAddress,
  abi: [
    {
      name: 'liquidity',
      type: 'function',
      stateMutability: 'view',
      inputs: [],
      outputs: [{ type: 'uint128' }],
    },
  ],
  functionName: 'liquidity',
});

const pool = new Pool(tokenIn, tokenOut, fee, slot0[0].toString(), liquidity.toString(), slot0[1]);

// 2. Build route and trade
const route = new V3Route([pool], tokenIn, tokenOut);
const trade = RouterTrade.createUncheckedTrade({
  route,
  inputAmount: amountIn,
  outputAmount: expectedOut,
  tradeType: TradeType.EXACT_INPUT,
});

// 3. Get calldata
const { calldata, value } = SwapRouter.swapCallParameters(trade, {
  slippageTolerance: new Percent(50, 10000), // 0.5%
  recipient: walletAddress,
  deadline: Math.floor(Date.now() / 1000) + 1800,
});

// 4. Execute with viem
const hash = await walletClient.sendTransaction({
  to: UNIVERSAL_ROUTER_ADDRESS,
  data: calldata,
  value: BigInt(value),
});

Low-Level Approach (Manual Commands)

For custom flows (fee collection, complex routing), use RoutePlanner directly:

import { RoutePlanner, CommandType, ROUTER_AS_RECIPIENT } from '@uniswap/universal-router-sdk';
import { encodeRouteToPath } from '@uniswap/v3-sdk';

// Special addresses
const MSG_SENDER = '0x0000000000000000000000000000000000000001';
const ADDRESS_THIS = '0x0000000000000000000000000000000000000002';

Example: V3 Swap with Manual Commands

import { RoutePlanner, CommandType } from '@uniswap/universal-router-sdk';
import { encodeRouteToPath, Route } from '@uniswap/v3-sdk';

async function swapV3Manual(route: Route, amountIn: bigint, amountOutMin: bigint) {
  const planner = new RoutePlanner();

  // Encode V3 path from route
  const path = encodeRouteToPath(route, false); // false = exactInput

  planner.addCommand(CommandType.V3_SWAP_EXACT_IN, [
    MSG_SENDER, // recipient
    amountIn, // amountIn
    amountOutMin, // amountOutMin
    path, // encoded path
    true, // payerIsUser
  ]);

  return executeRoute(planner);
}

Example: ETH to Token (Wrap + Swap)

async function swapEthToToken(route: Route, amountIn: bigint, amountOutMin: bigint) {
  const planner = new RoutePlanner();
  const path = encodeRouteToPath(route, false);

  // 1. Wrap ETH to WETH (keep in router)
  planner.addCommand(CommandType.WRAP_ETH, [ADDRESS_THIS, amountIn]);

  // 2. Swap WETH → Token (payerIsUser = false since using router's WETH)
  planner.addCommand(CommandType.V3_SWAP_EXACT_IN, [
    MSG_SENDER,
    amountIn,
    amountOutMin,
    path,
    false,
  ]);

  return executeRoute(planner, { value: amountIn });
}

Example: Token to ETH (Swap + Unwrap)

async function swapTokenToEth(route: Route, amountIn: bigint, amountOutMin: bigint) {
  const planner = new RoutePlanner();
  const path = encodeRouteToPath(route, false);

  // 1. Swap Token → WETH (output to router)
  planner.addCommand(CommandType.V3_SWAP_EXACT_IN, [
    ADDRESS_THIS,
    amountIn,
    amountOutMin,
    path,
    true,
  ]);

  // 2. Unwrap WETH to ETH
  planner.addCommand(CommandType.UNWRAP_WETH, [MSG_SENDER, amountOutMin]);

  return executeRoute(planner);
}

Example: Fee Collection with PAY_PORTION

async function swapWithFee(route: Route, amountIn: bigint, feeRecipient: Address, feeBips: number) {
  const planner = new RoutePlanner();
  const path = encodeRouteToPath(route, false);
  const outputToken = route.output.wrapped.address;

  // Swap to router (ADDRESS_THIS)
  planner.addCommand(CommandType.V3_SWAP_EXACT_IN, [ADDRESS_THIS, amountIn, 0n, path, true]);

  // Pay fee portion (e.g., 30 bips = 0.3%)
  planner.addCommand(CommandType.PAY_PORTION, [outputToken, feeRecipient, feeBips]);

  // Sweep remainder to user
  planner.addCommand(CommandType.SWEEP, [outputToken, MSG_SENDER, 0n]);

  return executeRoute(planner);
}

Execute Route Helper

import { UNIVERSAL_ROUTER_ADDRESS } from '@uniswap/universal-router-sdk';

const ROUTER_ABI = [
  {
    name: 'execute',
    type: 'function',
    stateMutability: 'payable',
    inputs: [
      { name: 'commands', type: 'bytes' },
      { name: 'inputs', type: 'bytes[]' },
      { name: 'deadline', type: 'uint256' },
    ],
    outputs: [],
  },
] as const;

async function executeRoute(planner: RoutePlanner, options?: { value?: bigint }) {
  const deadline = BigInt(Math.floor(Date.now() / 1000) + 1800);
  const routerAddress = UNIVERSAL_ROUTER_ADDRESS('2.0', 1); // version, chainId

  const { request } = await publicClient.simulateContract({
    address: routerAddress,
    abi: ROUTER_ABI,
    functionName: 'execute',
    args: [planner.commands, planner.inputs, deadline],
    account,
    value: options?.value ?? 0n,
  });

  return walletClient.writeContract(request);
}

Command Cheat Sheet

Fee Tiers

Common Integration Patterns

Frontend Swap Hook (React)

Note: Ensure you've set up the Buffer polyfill and CORS proxy (see Critical Implementation Notes). For wagmi v2 useWalletClient() pitfalls, see wagmi v2 Integration Pitfalls below.

import { isAddress, isHex } from 'viem';
import { useWalletClient } from 'wagmi';

// In browser apps, use your CORS proxy path instead (see CORS Proxy Configuration)
// e.g., const API_URL = '/api/uniswap';
const API_URL = 'https://trade-api.gateway.uniswap.org/v1';

function useSwap() {
  const { data: walletClient } = useWalletClient();
  const [quoteResponse, setQuoteResponse] = useState(null);
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState(null);

  const getQuote = async (params) => {
    setLoading(true);
    setError(null);
    try {
      const response = await fetch(`${API_URL}/quote`, {
        method: 'POST',
        headers: {
          'Content-Type': 'application/json',
          'x-api-key': API_KEY,
          'x-universal-router-version': '2.0',
        },
        body: JSON.stringify(params),
      });
      const data = await response.json();
      if (!response.ok) throw new Error(data.detail || 'Quote failed');
      setQuoteResponse(data); // Store the FULL response, not just data.quote
    } catch (err) {
      setError(err.message);
    } finally {
      setLoading(false);
    }
  };

  const executeSwap = async (permit2Signature?: string) => {
    if (!quoteResponse) throw new Error('No quote available');

    // Strip null fields and spread quote response into body
    const { permitData, permitTransaction, ...cleanQuote } = quoteResponse;
    const swapRequest: Record<string, unknown> = { ...cleanQuote };

    // CRITICAL: permitData handling differs by routing type
    const isUniswapX =
      quoteResponse.routing === 'DUTCH_V2' ||
      quoteResponse.routing === 'DUTCH_V3' ||
      quoteResponse.routing === 'PRIORITY';

    if (isUniswapX) {
      // UniswapX: signature only — permitData must NOT be sent to /swap
      // (permitData is used locally to sign the order, not submitted to the API)
      if (permit2Signature) swapRequest.signature = permit2Signature;
    } else {
      // CLASSIC: both signature and permitData required together, or both omitted
      if (permit2Signature && permitData && typeof permitData === 'object') {
        swapRequest.signature = permit2Signature;
        swapRequest.permitData = permitData;
      }
    }

    const swapResponse = await fetch(`${API_URL}/swap`, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'x-api-key': API_KEY,
        'x-universal-router-version': '2.0',
      },
      body: JSON.stringify(swapRequest),
    });
    const data = await swapResponse.json();
    if (!swapResponse.ok) throw new Error(data.detail || 'Swap failed');

    // CRITICAL: Validate response before broadcasting
    if (!data.swap?.data || data.swap.data === '' || data.swap.data === '0x') {
      throw new Error('Empty swap data - quote may have expired. Please refresh.');
    }

    // Send transaction via wallet (walletClient from useWalletClient())
    if (!walletClient) throw new Error('Wallet not connected');
    const tx = await walletClient.sendTransaction(data.swap);
    return tx;
  };

  return { quote: quoteResponse?.quote, loading, error, getQuote, executeSwap };
}

wagmi v2 Integration Pitfalls

The useWalletClient() hook from wagmi v2 can return undefined even when the wallet is connected — it resolves asynchronously. This causes "wallet not connected" errors at swap time. Additionally, the returned client needs a chain for sendTransaction() to work.

Recommended pattern — use @wagmi/core action functions at swap time instead of hooks:

import { getWalletClient, getPublicClient, switchChain } from '@wagmi/core';
import type { Config } from 'wagmi';

async function executeSwapTransaction(
  config: Config,
  chainId: number,
  swapTx: { to: string; data: string; value: string }
) {
  // 1. Ensure the wallet is on the correct chain
  await switchChain(config, { chainId });

  // 2. Get wallet client with explicit chainId — avoids undefined and missing chain
  const walletClient = await getWalletClient(config, { chainId });

  // 3. Execute the swap
  const hash = await walletClient.sendTransaction({
    to: swapTx.to as `0x${string}`,
    data: swapTx.data as `0x${string}`,
    value: BigInt(swapTx.value || '0'),
  });

  // 4. Wait for confirmation
  const publicClient = getPublicClient(config, { chainId });
  if (!publicClient) throw new Error(`No public client configured for ch

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