Ethereum: Getting error “Could not fetch chain ID. Is your RPC URL correct?” in metamask while trying to add Anvil running on wsl

Troubleshooting Ethereum Integration with Metamask and Anvil

As a developer building decentralized applications (dApps) on Ethereum, it’s not uncommon to encounter issues when integrating with third-party wallets like MetaMask and Anvil. Recently, I encountered an error message that has been plaguing many users: “Could not fetch chain ID. Is your RPC URL correct?” This problem is quite common in the context of running dApps on Windows Subsystem for Linux (WSL) or using a headless Metamask instance.

What’s happening under the hood?

The Ethereum blockchain uses a unique identifier called the chainID to identify each block chain. When you run your MetaMask or Anvil instance, it needs to be able to fetch this information from the Ethereum network. However, if the RPC URL (Remote Procedure Call) of your Metamask or Anvil instance is incorrect, it will fail to retrieve the blockchain’s ID.

Possible Causes:

• Incorrect RPC URL: Make sure that you’ve entered the correct RPC URL in both your MetaMask and Anvil instances.

• Network connectivity issues: Ensure that your WSL environment has a stable internet connection (you can test this by running curl -v to check network availability).

• Incorrect chain ID: It's possible that you've set the Ethereum mainnet chain ID incorrectly in your MetaMask or Anvil instance.

• WSL configuration issues: Sometimes, WSL configurations can cause issues with RPC URLs.

Troubleshooting steps:

• Check your Metamask and Anvil instances for errors: Ensure that both instances are running correctly and have no authentication issues (e.g., incorrect wallet addresses or keys).

• Verify the RPC URL in your MetaMask instance

  : Check theWallet Addresssection of your MetaMask instance to ensure it's set to the correct address.

• Test your WSL environment for network connectivity: Run a simple test likecurl -v to check if you can reach the Ethereum network.

• Update your chain ID: If you’ve changed the Ethereum mainnet chain ID, ensure that it’s set correctly in both your MetaMask and Anvil instances.

Solutions:

• Check your WSL configuration: Ensure that your WSL environment is configured to use the correct RPC URL for your Ethereum instance.

• Reset Metamask or Anvil instance: If you’re using a headless instance, try resetting it by deleting the metamask.conf file and restarting the process.

Conclusion:

To resolve the “Could not fetch chain ID” error in MetaMask with Anvil running on WSL, ensure that:

• Your Metamask and Anvil instances are running correctly.

• The RPC URL is correct for both instances.

• Network connectivity issues have been resolved (e.g., check your internet connection).

• You’ve verified the Ethereum mainnet chain ID.

By following these troubleshooting steps and solutions, you should be able to resolve this issue and get started with building your dApps on Ethereum.