Chain ID
Also known as: Blockchain Identifier, EVM Chain Code, Network ID
A unique identifier assigned to each blockchain network to prevent transaction replay across chains.
A Chain ID is a unique numerical identifier assigned to blockchain networks to distinguish them from each other. It’s essential for ensuring transaction security and preventing replay attacks—where the same signed transaction could be submitted to multiple chains. Chain IDs are particularly relevant in networks that are EVM-compatible, such as Ethereum, BSC, or Polygon. Developers use chain IDs in wallets, RPC configurations, and smart contracts to direct transactions to the correct network. Hard forks and testnets also use different Chain IDs to avoid cross-network confusion.