Choose your Chain ID

Choose Chain ID for your L2

Choose a Chain ID that uniquely identifies your chain. It will be used to set up MetaMask later.

98989897

Check that the Chain ID it not taken already using https://chainlist.org/?testnets=true.

MetaMask uses ChainList to suggest chain details such as name and currency, and will complain if you use an existing Chain ID. So make sure to choose a new unique Chain ID.

If you will deploy your chain for public use, then add your chain to ChainList as well.