viem

<objective> Build blockchain interactions using viem for Ethereum clients, transactions, signing, and smart contract interactions. Viem is the modern replacement for ethers.js with better TypeScript support. </objective>

<mcp_first> CRITICAL: Always fetch viem documentation before implementing.

MCPSearch({ query: "select:mcp__plugin_devtools_context7__query-docs" })

// Client patterns
mcp__context7__query_docs({
  context7CompatibleLibraryID: "/wevm/viem",
  topic: "createPublicClient createWalletClient"
})

// Contract interactions
mcp__context7__query_docs({
  context7CompatibleLibraryID: "/wevm/viem",
  topic: "readContract writeContract simulateContract"
})

// Signing
mcp__context7__query_docs({
  context7CompatibleLibraryID: "/wevm/viem",
  topic: "signMessage signTypedData EIP-712"
})

// Encoding
mcp__context7__query_docs({
  context7CompatibleLibraryID: "/wevm/viem",
  topic: "encodeFunctionData decodeFunctionResult encodeAbiParameters"
})

</mcp_first>

<quick_start> Create clients:

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

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

const walletClient = createWalletClient({
  chain: mainnet,
  transport: http(),
  account: privateKeyToAccount("0x..."),
});

Read contract:

const balance = await publicClient.readContract({
  address: "0x...",
  abi: erc20Abi,
  functionName: "balanceOf",
  args: [userAddress],
});

Write contract:

const hash = await walletClient.writeContract({
  address: "0x...",
  abi: erc20Abi,
  functionName: "transfer",
  args: [recipient, amount],
});

const receipt = await publicClient.waitForTransactionReceipt({ hash });

</quick_start>

<client_types> | Client | Purpose | Example Use | |--------|---------|-------------| | PublicClient | Reading blockchain data | getBlockNumber(), readContract() | | WalletClient | Transaction signing/sending | sendTransaction(), signMessage() | | TestClient | Testing and simulation | mine(), setBalance() | | BundlerClient | ERC-4337 User Operations | sendUserOperation() | </client_types>

<utilities> Unit conversions:

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

parseEther("1.5");           // 1500000000000000000n
formatEther(1500000000000000000n);  // "1.5"
parseUnits("100", 6);        // 100000000n (USDC)
formatUnits(100000000n, 6);  // "100"

Address utilities:

import { getAddress, isAddress } from "viem";

getAddress("0xabc...");  // Checksummed address
isAddress("0x...");      // Validates format

</utilities>

<constraints> Banned: SSRF protection for config-sourced URLs (they're developer-controlled)

Required:

• Lazy initialization for chain resolution
• Client caching by network name
• WebSocket cleanup on destroy/refresh
• Type-safe ABI interactions

</constraints>

<success_criteria>

• [ ] Context7 docs fetched for current API
• [ ] Uses lazy chain resolution
• [ ] Caches clients by network name
• [ ] Type-safe ABI interactions
• [ ] Proper error handling for blockchain ops

</success_criteria>