Bip39 Checksum. Firstly you should store it SEPARATELY from the seed. Acquiring your seed along with your passphrase in exactly the same location defeats the purpose of using a passphrase to begin with. What constitutes a "very good wallet" is one that has obvious, simple to entry documentation on supported https://socialrator.com/story9940170/bip39-wallets-https-linktr-ee-bip39-getting-my-ian-coleman-bip39-to-work