Verifying Your Mnemonic Phrase

Ensure you can regenerate the same eth2 key pairs by restoring your validator_keys

Using the pre-built staking-deposit-cli executable,

cd $HOME/staking-deposit-cli 
./deposit existing-mnemonic --chain mainnet

When the pubkey in both keystore files are identical, this means your mnemonic phrase is veritably correct. Other fields will be different because of salting.