viem-integration

---

name: viem-integration description: Integrate EVM blockchains using viem. Use when user says "read blockchain data", "send transaction", "interact with smart contract", "connect to Ethereum", "use viem", "use wagmi", "wallet integration", "viem setup", or mentions blockchain/EVM development with TypeScript. allowed-tools: Read, Write, Edit, Glob, Grep, Bash(npm:), Bash(npx:), WebFetch, Task(subagent_type:viem-integration-expert) model: opus license: MIT metadata: author: uniswap version: '1.0.0'

viem Integration

Integrate EVM blockchains using viem for TypeScript/JavaScript applications.

Quick Decision Guide

Building...	Use This
Node.js script/backend	viem with http transport
React/Next.js frontend	wagmi hooks (built on viem)
Real-time event monitoring	viem with webSocket transport
Browser wallet integration	wagmi or viem custom transport

Installation

# Core library
npm install viem

# For React apps, also install wagmi
npm install wagmi viem @tanstack/react-query

Core Concepts

Clients

viem uses two client types:

Client	Purpose	Example Use
PublicClient	Read-only operations	Get balances, read contracts, fetch logs
WalletClient	Write operations	Send transactions, sign messages

Transports

Transport	Use Case
http()	Standard RPC calls (most common)
webSocket()	Real-time event subscriptions
custom()	Browser wallets (window.ethereum)

Chains

viem includes 50+ chain definitions. Import from viem/chains:

import { mainnet, arbitrum, optimism, base, polygon } from 'viem/chains';

---

Input Validation Rules

Before interpolating ANY user-provided value into generated TypeScript code:

• Ethereum addresses: MUST match ^0x[a-fA-F0-9]{40}$ — use viem's isAddress() for validation
• Chain IDs: MUST be from viem's supported chain definitions
• Private keys: MUST NEVER be hardcoded — always use process.env.PRIVATE_KEY with runtime validation
• RPC URLs: MUST use https:// or wss:// protocols only
• ABI inputs: Validate types match expected Solidity types before encoding

Quick Start Examples

Read Balance

import { createPublicClient, http, formatEther } from 'viem';
import { mainnet } from 'viem/chains';

const client = createPublicClient({
  chain: mainnet,
  transport: http(),
});

const balance = await client.getBalance({
  address: '0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045',
});

console.log(`Balance: ${formatEther(balance)} ETH`);

Read Contract

import { createPublicClient, http, parseAbi } from 'viem';
import { mainnet } from 'viem/chains';

const client = createPublicClient({
  chain: mainnet,
  transport: http(),
});

const abi = parseAbi([
  'function balanceOf(address) view returns (uint256)',
  'function decimals() view returns (uint8)',
]);

const balance = await client.readContract({
  address: '0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48', // USDC
  abi,
  functionName: 'balanceOf',
  args: ['0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045'],
});

Send Transaction

import { createWalletClient, http, parseEther } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { mainnet } from 'viem/chains';

const account = privateKeyToAccount(process.env.PRIVATE_KEY as `0x${string}`);

const client = createWalletClient({
  account,
  chain: mainnet,
  transport: http(),
});

const hash = await client.sendTransaction({
  to: '0x...',
  value: parseEther('0.1'),
});

console.log(`Transaction hash: ${hash}`);

Write to Contract

import { createWalletClient, createPublicClient, http, parseAbi, parseUnits } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { mainnet } from 'viem/chains';

const account = privateKeyToAccount(process.env.PRIVATE_KEY as `0x${string}`);

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

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

const abi = parseAbi(['function transfer(address to, uint256 amount) returns (bool)']);

// Simulate first to catch errors
const { request } = await publicClient.simulateContract({
  address: '0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48',
  abi,
  functionName: 'transfer',
  args: ['0x...', parseUnits('100', 6)],
  account,
});

// Execute the transaction
const hash = await walletClient.writeContract(request);

// Wait for confirmation
const receipt = await publicClient.waitForTransactionReceipt({ hash });
console.log(`Confirmed in block ${receipt.blockNumber}`);

---

Reference Documentation

For deeper coverage of specific topics:

Topic	Reference File
Client setup, transports, chains	Clients & Transports
Reading blockchain data	Reading Data
Sending transactions	Writing Transactions
Private keys, HD wallets	Accounts & Keys
ABI handling, multicall	Contract Patterns
React/wagmi hooks	Wagmi React

---

Related Plugins

Once you're comfortable with viem basics, the uniswap-trading plugin provides comprehensive Uniswap swap integration:

• Uniswap Trading API integration
• Universal Router SDK usage
• Token swap implementations

Install it with: claude plugin add @uniswap/uniswap-trading

---

Common Utilities

Unit Conversion

import { parseEther, formatEther, parseUnits, formatUnits } from 'viem';

// ETH
parseEther('1.5'); // 1500000000000000000n (wei)
formatEther(1500000000000000000n); // "1.5"

// Tokens (e.g., USDC with 6 decimals)
parseUnits('100', 6); // 100000000n
formatUnits(100000000n, 6); // "100"

Address Utilities

import { getAddress, isAddress } from 'viem';

isAddress('0x...'); // true/false
getAddress('0x...'); // checksummed address

Hashing

import { keccak256, toHex } from 'viem';

keccak256(toHex('hello')); // 0x1c8aff950685c2ed4bc3174f3472287b56d9517b9c948127319a09a7a36deac8

---

Error Handling

viem throws typed errors that can be caught and handled:

import { ContractFunctionExecutionError, InsufficientFundsError } from 'viem'

try {
  await client.writeContract(...)
} catch (error) {
  if (error instanceof ContractFunctionExecutionError) {
    console.error('Contract call failed:', error.shortMessage)
  }
  if (error instanceof InsufficientFundsError) {
    console.error('Not enough ETH for gas')
  }
}

---

Resources

• viem Documentation
• wagmi Documentation
• viem GitHub
• wagmi GitHub