Bip39 seed phrase generator https://go.bubbl.us/ebe220/f17a?/Bookmarks Checksum generation: A checksum is produced from this entropy working with SHA-256 hashing, which allows verify the mnemonic's integrity later on. For words that only have three letters, there isn't any 4th letter. Such as with the word “add”, there isn't any much more letters https://www.sbnation.com/users/typhanhmdy