Generate secure BIP39 mnemonic phrases (12-24 words) with optional passphrase, and derive the 512-bit seed.
Generate secure BIP39 mnemonic phrases (12-24 words) with optional passphrase, and derive the 512-bit seed. Generate secure BIP39 mnemonic phrases (12-24 words) with optional passphrase, and derive the 512-bit seed.
Mnemonic phrase
BIP32 seed (512-bit hex)
Entropy used (hex)
Background
What BIP39 is
BIP39 (Bitcoin Improvement Proposal 39) defines how a wallet can represent
its entropy as a human-readable mnemonic phrase. Instead of writing down a
long hexadecimal seed, a user writes 12 to 24 words drawn from a fixed
2048-word list (currently English, with many localized lists available). The
words are not random text: the last word contains a checksum derived from
SHA-256 of the entropy, so a mistyped phrase can be detected on the spot.
How a phrase maps to a seed
Generation starts with random entropy of 128 to 256 bits. The entropy is
hashed with SHA-256, and the first entropy bits / 32 bits of the digest are
appended as a checksum, making the total bit length a multiple of 11. Each
11-bit group indexes one word in the 2048-word list (2^11 = 2048). To derive
the 512-bit seed, the phrase is normalized with NFKD and fed to PBKDF2-HMAC-
SHA512 with the salt mnemonic + an optional passphrase, iterated 2048 times.
The same passphrase must be supplied to recover the wallet; a different
passphrase yields a completely different seed.
Using the generator
Pick how many words you want (12, 15, 18, 21, or 24). The generator draws
fresh entropy from the browser's cryptographically secure random source, so
every click produces a new, unpredictable phrase. If you add a passphrase,
the seed derivation changes accordingly -- remember it exactly, because it is
an essential part of the wallet secret. The seed is shown as 128 hex
characters (512 bits); it is the direct input to BIP32 hierarchical
deterministic wallet derivation.
Security guidance
A mnemonic phrase IS the wallet: anyone who possesses it controls the funds,
regardless of where it was generated. Keep it offline, never paste it into a
chat or email, and prefer writing it on paper over screenshots or cloud
notes. The 2048-word checksum protects against typos, not against theft.
Strong entropy (24 words = 256 bits) leaves no practical brute-force margin,
so the only realistic risk is how you store and transmit the phrase. This
generator runs fully in your browser: the phrase and seed never leave the
page. Clear the output and reload after use if you are on a shared machine.
Frequently asked questions
Is the checksum word really necessary?
Yes. Without it, a single typo could silently produce a different wallet. With BIP39, one wrong letter in the final word is caught by the SHA-256 checksum before you rely on the phrase.
Why do I need a passphrase on top of the words?
The passphrase acts as an extra factor mixed into the PBKDF2 salt. Even if someone reads your 12 words, they still need the passphrase to derive the seed. Losing it, however, means the wallet is unrecoverable.
Which word count should I choose?
12 words (128 bits) is the industry standard and safe for everyday wallets. Choose 24 words (256 bits) for extra margin against future threats or for high-value holdings. 15/18/21 exist for specific ecosystem requirements.
Can the same phrase generate multiple wallets?
No, the same phrase always derives the same seed (when the passphrase matches). Wallets that seem different are typically using different derivation paths or coins under BIP32/BIP44, not different seeds.
Is it safe to use an online generator?
This page runs entirely in your browser -- no phrase or seed is transmitted. Still, a compromised device or malicious browser extension can read anything on screen. For serious funds, generate on an air-gapped machine or a hardware wallet.
What is the seed used for?
The 512-bit seed is the root of a BIP32 hierarchical deterministic wallet. From it, wallets derive an infinite tree of private/public key pairs -- normally one per address or account -- using path-based derivation such as BIP44.