All data (mnemonic, private key and public key) are generated by your browser.
This tool is made with the Bip39 Library and others open source libraries.
This tool is not a Wallet/Portfolio. It generates only the datas you need to import in any wallet you want (Metamask). It means we don't offer any services to store or manage credentials neither we are a Wallet Provider.
Do not save or store mnemonic, seed, address and private key on computer without a strong crittography tool (Save always in app like Keepass2Android or similar).
Working always in offline mode.
About Mnemonic generation: Do not use sentences from books, movies or song.
You could restore from any Mnemonic you already have. But it's not our core business.
With Mnemonic and Seed you could generate many address/private key pairs as you want. Account generated is always the number 1 or 0 (array)