Is a tool to generate/verify/extract BIP39 seeds.
You could use it for many purposes in regards of BTC wallets.
You should use it offline (aka save the webpage in a html file and run it from a PC that is not connected to internet). In case your actual PC/browser is compromised.
Is a good tool
https://iancoleman.io/bip39/

I also recommend to bookmark this another amazing tool for LND aezeed wallets:
https://guggero.github.io/cryptography-toolkit/