viem

TypeScript interface for Ethereum and EVM-compatible chains. Provides low-level primitives for blockchain interaction with end-to-end type safety, minimal abstraction overhead, and tree-shakeable modules. The default client library for wagmi.

What You Probably Got Wrong

AI agents trained before 2024 confuse viem with ethers.js patterns. These are the critical differences.

• viem uses native bigint, not BigNumber -- There is no BigNumber class. All wei values are bigint. Use 100n literal syntax or BigInt("100"). Never use ethers.BigNumber.from().
• Address type is `0x${string}`, not plain string -- viem enforces checksummed 0x-prefixed addresses at the type level. Use getAddress() to normalize.
• Clients are not providers -- viem has PublicClient (reads), WalletClient (writes), and TestClient (anvil). There is no Provider or Signer concept.
• Transports replace connection URLs -- You pass http(), webSocket(), or custom() transports to clients, not raw RPC URLs as strings.
• ABIs must be as const -- For type inference to work, ABI arrays must use as const assertion. Without it, you lose all parameter/return type safety.
• simulateContract before writeContract -- viem separates simulation from execution. Always simulate first to catch reverts before sending a transaction.
• No default chain -- Every client requires an explicit chain parameter. There is no implicit mainnet default.
• parseEther returns bigint, not a wrapper -- parseEther("1.0") returns 1000000000000000000n, a raw bigint.

Quick Start