# Viem

> This skill should be used when the user asks about "viem", "viem client", "viem actions", "TypeScript Ethereum", "createPublicClient", "createWalletClient", "parseEther", "formatEther", "readContract", "writeContract", or mentions using viem for blockchain interactions. Use when this capability is needed.

- Skill: `tomevault-io/viem` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/viem`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/viem/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/viem

---


# Viem

## Overview

Viem is a TypeScript interface for Ethereum that provides low-level stateless primitives for interacting with the blockchain. It focuses on developer experience, stability, bundle size, and performance.

Key features:

- Automatic type safety and inference
- Tree-shakable lightweight modules
- Optimized encoding/parsing
- Composable APIs

## Core Concepts

| Concept        | Description                                                   |
| -------------- | ------------------------------------------------------------- |
| **Clients**    | `PublicClient`, `WalletClient`, `TestClient` - entry points   |
| **Transports** | Connection layer (`http`, `webSocket`, `custom`)              |
| **Actions**    | Operations like `getBlockNumber`, `sendTransaction`           |
| **Chains**     | Chain configurations (`mainnet`, `sepolia`, `arbitrum`, etc.) |

## Constants

Viem exports useful constants for common values:

```typescript
import { maxUint256, maxUint128, maxInt256, zeroAddress, zeroHash } from "viem";

// Max values for uint types
maxUint256; // 2n ** 256n - 1n
maxUint128; // 2n ** 128n - 1n

// Zero values
zeroAddress; // 0x0000000000000000000000000000000000000000
zeroHash; // 0x0000000000000000000000000000000000000000000000000000000000000000
```

## Utilities

### Unit Conversion

Convert between wei and human-readable values:

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

// ETH <-> Wei (18 decimals)
parseEther("1"); // 1000000000000000000n
formatEther(1000000000000000000n); // "1"

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

### ABI Utilities

Parse human-readable ABIs:

```typescript
import { parseAbi, parseAbiItem } from "viem";

const abi = parseAbi([
  "function balanceOf(address owner) view returns (uint256)",
  "function transfer(address to, uint256 amount) returns (bool)",
  "event Transfer(address indexed from, address indexed to, uint256 amount)",
]);

const item = parseAbiItem("function name() view returns (string)");
```

### Address Utilities

```typescript
import { getAddress, isAddress, isAddressEqual } from "viem";

// Checksum address
getAddress("0xabc..."); // "0xAbc..." (checksummed)

// Validation
isAddress("0x..."); // true/false
isAddressEqual("0xAbc...", "0xabc..."); // true (case-insensitive)
```

## Clients

### Public Client (Read Operations)

For querying blockchain state:

```typescript
import { createPublicClient, http } from "viem";
import { mainnet } from "viem/chains";

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

// Read operations
const blockNumber = await publicClient.getBlockNumber();
const balance = await publicClient.getBalance({ address: "0x..." });
const block = await publicClient.getBlock();
```

### Wallet Client (Write Operations)

For signing and sending transactions:

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

const account = privateKeyToAccount("0x...");

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

// Send transaction
const hash = await walletClient.sendTransaction({
  to: "0x...",
  value: parseEther("0.1"),
});
```

### Browser Wallet Client

For browser environments with injected wallets:

```typescript
import "viem/window";
import { createWalletClient, custom } from "viem";
import { mainnet } from "viem/chains";

const walletClient = createWalletClient({
  chain: mainnet,
  transport: custom(window.ethereum!),
});

// Request accounts
const [address] = await walletClient.requestAddresses();
```

### Extending Clients

Combine capabilities using `.extend()`:

```typescript
import { createWalletClient, http, publicActions } from "viem";
import { mainnet } from "viem/chains";

const client = createWalletClient({
  chain: mainnet,
  transport: http(),
}).extend(publicActions);

// Now supports both wallet and public actions
const balance = await client.getBalance({ address: "0x..." });
const hash = await client.sendTransaction({ to: "0x...", value: 1n });
```

## Contract Interactions

### Reading from Contracts

```typescript
import { createPublicClient, http } from "viem";
import { mainnet } from "viem/chains";

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

const abi = [
  {
    inputs: [{ name: "owner", type: "address" }],
    name: "balanceOf",
    outputs: [{ name: "", type: "uint256" }],
    stateMutability: "view",
    type: "function",
  },
] as const;

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

### Writing to Contracts

```typescript
const hash = await walletClient.writeContract({
  address: "0x...",
  abi,
  functionName: "transfer",
  args: ["0x...", parseUnits("100", 18)],
});
```

### Simulating Before Writing

Simulate a transaction before sending:

```typescript
const { request } = await publicClient.simulateContract({
  address: "0x...",
  abi,
  functionName: "transfer",
  args: ["0x...", parseUnits("100", 18)],
  account: "0x...",
});

const hash = await walletClient.writeContract(request);
```

## Account Types

### Local Accounts

For server-side or controlled environments:

```typescript
import { privateKeyToAccount, mnemonicToAccount } from "viem/accounts";

// From private key
const account = privateKeyToAccount("0x...");

// From mnemonic
const account = mnemonicToAccount("legal winner thank year wave sausage ...");
```

### JSON-RPC Accounts

For browser wallets:

```typescript
import "viem/window";

const [account] = await window.ethereum!.request({
  method: "eth_requestAccounts",
});
```

## Chain Configuration

### Built-in Chains

```typescript
import { mainnet, sepolia, arbitrum, optimism, polygon, base } from "viem/chains";

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

### Custom Chains

```typescript
import { defineChain } from "viem";

const customChain = defineChain({
  id: 123456,
  name: "My Chain",
  nativeCurrency: { name: "ETH", symbol: "ETH", decimals: 18 },
  rpcUrls: {
    default: { http: ["https://rpc.mychain.com"] },
  },
  blockExplorers: {
    default: { name: "Explorer", url: "https://explorer.mychain.com" },
  },
});
```

## Documentation

This skill provides a reference for common operations. For comprehensive documentation, fetch the full viem docs using context7 MCP:

```
Library ID: /wevm/viem
```

Use context7 to query specific topics:

- `clients` - Client types and configuration
- `actions` - Available actions (read, write, wallet)
- `accounts` - Local and JSON-RPC accounts
- `contract` - Contract interactions (`readContract`, `writeContract`)
- `abi` - ABI encoding/decoding utilities
- `chains` - Supported chains and custom chain configuration

### Fetching Documentation

To fetch viem documentation for a specific topic:

1. Resolve the library ID with `mcp__context7__resolve-library-id` (or use `/wevm/viem` directly)
2. Call `mcp__context7__get-library-docs` with the topic parameter

Example topics: `"getting started"`, `"wallet client"`, `"send transaction"`, `"read contract"`.

---
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<!-- tomevault:4.0:skill_md:2026-04-11 -->