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/