Bip39-Standalone Or for pretty significant safety, you could "roll your own private" seed phrase with dice or maybe a calculator as offline approaches. The application of the wallet works by using a complete set of words taken from a vocabulary; at that every word is assigned to a specific variety. https://guidemysocial.com/story3903121/bip39-12-word-seed-phrase-list-the-fact-about-bip39-phrase-that-no-one-is-suggesting