Detect a user's network

It's important to keep track of the user's network chain ID because all RPC requests are submitted to the currently connected network.

Use the eth_chainId RPC method to detect the chain ID of the user's current network. Listen to the chainChanged provider event to detect when the user changes networks.

For example, the following code detects a user's network and when the user changes networks:

index.js

const chainId = await provider // Or window.ethereum if you don't support EIP-6963.
  .request({ method: "eth_chainId" });

provider // Or window.ethereum if you don't support EIP-6963.
  .on("chainChanged", handleChainChanged);

function handleChainChanged(chainId) {
  // We recommend reloading the page, unless you must do otherwise.
  window.location.reload();
}

Chain IDs

These are the chain IDs of the Ethereum networks that MetaMask supports by default. Consult chainid.network for more.

Hex	Decimal	Network
0x1	1	Ethereum main network (Mainnet)
0x5	5	Goerli test network
0xaa36a7	11155111	Sepolia test network
0xe704	59140	Linea Goerli test network
0x539	1337	Localhost test networks