viem

Viem Skill

Version: Viem 2.x | Official Docs

Viem is the modern TypeScript interface for Ethereum. This skill ensures correct patterns for contract interactions, client setup, and type safety.

Quick Reference

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

Critical Patterns

1. Client Setup

Public Client (read-only operations):

const publicClient = createPublicClient({
  chain: mainnet,
  transport: http('https://eth-mainnet.g.alchemy.com/v2/YOUR_KEY'),
})

Wallet Client (write operations):

const account = privateKeyToAccount('0x...')
const walletClient = createWalletClient({
  account,
  chain: mainnet,
  transport: http('https://eth-mainnet.g.alchemy.com/v2/YOUR_KEY'),
})

2. ABI Type Safety (CRITICAL)

Always use as const for ABIs to get full type inference:

// ✅ CORRECT - Full type safety
const abi = [
  {
    name: 'balanceOf',
    type: 'function',
    stateMutability: 'view',
    inputs: [{ name: 'owner', type: 'address' }],
    outputs: [{ name: '', type: 'uint256' }],
  },
] as const

// ❌ WRONG - No type inference
const abi = [{ name: 'balanceOf', ... }] // Missing `as const`

3. Contract Read Pattern

const balance = await publicClient.readContract({
  address: '0x...', // Contract address
  abi,
  functionName: 'balanceOf',
  args: ['0x...'], // Args are fully typed when using `as const`
})

4. Contract Write Pattern (Simulate First!)

Always simulate before writing to catch errors early:

// Step 1: Simulate
const { request } = await publicClient.simulateContract({
  account,
  address: '0x...',
  abi,
  functionName: 'transfer',
  args: ['0x...', 1000000n], // Use BigInt for uint256
})

// Step 2: Execute
const hash = await walletClient.writeContract(request)

// Step 3: Wait for receipt
const receipt = await publicClient.waitForTransactionReceipt({ hash })

5. Event Watching

const unwatch = publicClient.watchContractEvent({
  address: '0x...',
  abi,
  eventName: 'Transfer',
  onLogs: (logs) => {
    for (const log of logs) {
      console.log(log.args.from, log.args.to, log.args.value)
    }
  },
})

// Clean up
unwatch()

6. Multicall for Batch Reads

const results = await publicClient.multicall({
  contracts: [
    { address: '0x...', abi, functionName: 'balanceOf', args: ['0x...'] },
    { address: '0x...', abi, functionName: 'totalSupply' },
  ],
})
// results[0].result, results[1].result

Common Mistakes

Mistake	Fix
Missing as const on ABI	Add as const for type inference
Using Number for amounts	Use BigInt literals: 1000000n
Writing without simulate	Always simulateContract first
Hardcoding gas	Let viem estimate, or use gas: await publicClient.estimateGas(...)
Not awaiting receipts	Use waitForTransactionReceipt for confirmation

Chain Configuration

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

// Custom chain
const customChain = {
  id: 123,
  name: 'My Chain',
  nativeCurrency: { name: 'ETH', symbol: 'ETH', decimals: 18 },
  rpcUrls: {
    default: { http: ['https://rpc.mychain.com'] },
  },
}

Error Handling

import { BaseError, ContractFunctionRevertedError } from 'viem'

try {
  await publicClient.simulateContract({ ... })
} catch (err) {
  if (err instanceof BaseError) {
    const revertError = err.walk(e => e instanceof ContractFunctionRevertedError)
    if (revertError instanceof ContractFunctionRevertedError) {
      const errorName = revertError.data?.errorName
      // Handle specific revert reason
    }
  }
}

References

For detailed patterns, see:

• references/contract-patterns.md - Advanced contract interaction patterns
• references/common-errors.md - Error handling and debugging guide
• Viem Documentation - Official docs
• Viem GitHub - Source and releases