Bip39 Github. Thanks to the cryptographic style and design of BIP-39, a weak passphrase isn't going to reduce the protection of the other wallets or enable reveal the seed words. Any one else who discovers the phrase can steal the bitcoins. It needs to be kept magic formula, for example https://privatebookmark.com/story19047601/bip39-https-linktr-ee-bip39-a-simple-key-for-bip39-unveiled