The eth_chainId method returns the current network/chain ID, which is crucial for signing replay-protected transactions as introduced in EIP-155. This simple yet essential method helps ensure transactions are executed on the intended network and prevents transaction replay attacks.

Use Cases

Verifying the current network connection in wallets and DApps
Implementing transaction replay protection
Building network-specific logic in multichain applications
Cross-chain application development and switching
Transaction signing validation
Network detection for user interfaces
Automated network switching in web3 applications

Method Details

This is a straightforward query method that returns the chain ID of the connected network in hexadecimal format. It requires no parameters and is extremely lightweight.

Parameters:

Parameters is empty

Returns:

resultstring

The chain ID in hexadecimal format

Response Example

{
	"jsonrpc": "2.0",
	"id": 1,
	"result": "0x1" // Represents Ethereum Mainnet (Chain ID: 1)
}

Common Chain IDs

0x1 (1): Ethereum Mainnet
0x5 (5): Goerli Testnet
0xAA36A7 (11155111): Sepolia Testnet
0x89 (137): Polygon Mainnet
0xA (10): Optimism
0xA4B1 (42161): Arbitrum One
0x38 (56): BNB Smart Chain
0xA86A (43114): Avalanche C-Chain

Understanding EIP-155

EIP-155 introduced replay protection by including the chain ID in transaction signatures. Prior to this improvement, a transaction signed for one network could potentially be replayed on another network or fork. The eth_chainId method is essential for implementing this protection, as it allows applications to get the correct chain ID value to include in transaction signatures.

eth_chainId