You can enter an existing BIP39 mnemonic, or generate a new random one. Typing your own twelve words will probably not work how you expect since the words require a particular structure (the last word contains a checksum).
For more info see the BIP39 spec.
Generate a random mnemonic, or enter your own below
Read more at the official BIP39 spec
Read more at the official BIP32 spec
See the demo at bip32.org
Read more at the official BIP44 spec
Read more at the official BIP49 spec
Read more at the official BIP85 spec
Entropy values should not include the BIP39 checksum. This is automatically added by the tool.
Entropy values must be sourced from a strong source of randomness. This means flipping a fair coin, rolling a fair dice, noise measurements, etc. Do NOT use phrases from books, lyrics from songs, your birthday or street address, keyboard mashing, or anything you think is random because chances are overwhelming it isn't random enough for the needs of this tool.
Do not store entropy.
Storing entropy (such as keeping a deck of cards in a specific shuffled order) is unreliable compared to storing a mnemonic. Instead of storing entropy, store the mnemonic generated from the entropy. Steganography may be beneficial when storing the mnemonic.
The random mnemonic generator on this page uses a cryptographically secure random number generator. The built-in random generator can generally be trusted more than your intuition about randomness. If cryptographic randomness isn't available in your browser, this page will show a warning, and the generate button will not work. In that case, you might use your entropy source.
You are not a good source of entropy.
Card entropy has been implemented assuming cards are replaced, not drawn one after another. A full deck with replacement generates 232 bits of entropy (21 words). A full deck without replacement generates 225 bits of entropy (21 words). Card entropy changed significantly from v0.4.3 to v0.5.0. The old version can be accessed at https://github.com/iancoleman/bip39/releases/tag/0.4.3 or https://web.archive.org/web/20201018232020/https://iancoleman.io/bip39/
What is PBKDF2 (Password-Based Key Derivation Function 2) ?
Please refer to this wikipedia article for more detail. Mail about PBKDF2 security here.
Wallet software that implement BIP39 only use 2048 iterations as a norm. Increasing this parameter will increase security against brute-force attacks, but you must store this new parameter. However, as long as you back up your BIP39 seed, you will not risk losing your fund. To access them with custom PBKDF2 iterations, use this file (or other) to compute your targeted BIP39 seed.
Using less than 2048 PBKDF2 iterations is insecure without strong optional BIP39 Passphrase.