Generate BIP39 Mnemonic Phrases Online

About the BIP39 Mnemonic Generator

The BIP39 Mnemonic Generator creates BIP39-compliant mnemonic seed phrases — the human-readable backup format used by Bitcoin, Ethereum, and most modern cryptocurrency hardware and software wallets. Choose a word count (12, 18, or 24 words), generate a phrase from the official BIP39 word list, and optionally derive the corresponding seed bytes for testing wallet code and verifying your key derivation implementation.

How to Use

• Select the phrase length: 12 words (128-bit entropy), 18 words (192-bit), or 24 words (256-bit).
• Optionally enter a BIP39 passphrase (also called the "25th word"). Leave blank for a standard wallet with no extra passphrase.
• Click Generate. The tool produces a random mnemonic phrase using the official English BIP39 word list.
• The corresponding 512-bit seed (derived via PBKDF2-HMAC-SHA512) is displayed for development and testing use.
• Use Validate to check whether an existing mnemonic phrase is valid BIP39 (correct word count, all words from the word list, valid checksum).

How BIP39 Mnemonics Work

BIP39 converts cryptographic entropy into a sequence of English words:

• Entropy generation — A random sequence of 128, 192, or 256 bits is generated using a cryptographically secure random number generator.
• Checksum — The SHA-256 hash of the entropy is computed and the first N bits are appended as a checksum (where N = entropy_bits / 32). This is why mnemonics have a specific last word — it encodes the checksum.
• Encoding — The entropy + checksum bits are split into 11-bit groups. Each group maps to one word from the BIP39 word list (2,048 words total). 12 words encode 132 bits (128 + 4 checksum); 24 words encode 264 bits (256 + 8 checksum).
• Seed derivation — The mnemonic phrase (and optional passphrase) are passed through PBKDF2-HMAC-SHA512 with 2,048 iterations to produce a 512-bit seed. This seed is the root for BIP32 HD wallet key derivation.

12 vs 18 vs 24 Words

• 12 words (128-bit entropy) — 2¹²⁸ possible phrases. Sufficient for any practical security requirement — brute-forcing 128-bit entropy is computationally infeasible. The default for most software wallets (MetaMask, Trust Wallet).
• 18 words (192-bit entropy) — 2¹⁹² possible phrases. Rarely used; provides a wider margin between current and theoretical future attack capabilities.
• 24 words (256-bit entropy) — 2²⁵⁶ possible phrases. The standard for hardware wallets (Ledger, Trezor) and high-value storage. Preferred for long-term cold storage where the phrase is backed up physically.

The BIP39 Passphrase

BIP39 supports an optional passphrase (sometimes called the "25th word") that is combined with the mnemonic during seed derivation:

• A different passphrase produces a completely different seed and wallet — one mnemonic can access an unlimited number of distinct wallets.
• A passphrase adds an extra layer of security: an attacker who obtains the mnemonic cannot access funds without also knowing the passphrase.
• Losing the passphrase permanently loses access to the wallet, just as losing the mnemonic does. Store both securely and separately.
• An empty passphrase is a valid default — it produces the standard wallet that most tools create.

Security and Safe Use

• Never generate production seed phrases in an online tool. This generator is intended for development, testing, and learning how BIP39 works — not for securing real funds. Generate production mnemonics on a hardware wallet or air-gapped device.
• Never type or paste a real mnemonic into any website. A phrase for a funded wallet should never touch an internet-connected device. This tool is safe to use for test phrases with no funds.
• Back up physically. Mnemonic phrases should be written on paper or engraved on metal and stored in multiple secure locations. Screenshot or digital storage of a funded wallet seed phrase is a significant security risk.

Frequently Asked Questions

What is the BIP39 word list?

The BIP39 word list is a curated set of 2,048 English words selected for distinctiveness — each word is uniquely identifiable from its first 4 characters, words are easy to spell correctly, and similar-sounding words were excluded to reduce transcription errors. The list is standardised and identical across all BIP39-compatible wallets.

Are BIP39 mnemonics compatible across all wallets?

A BIP39 mnemonic generated by one wallet can be imported into any other BIP39-compatible wallet to recover the same keys. However, different wallets use different BIP32 derivation paths (e.g., MetaMask uses m/44'/60'/0'/0 for Ethereum; Ledger Live uses m/44'/60'/0' by default). If recovering a wallet in a different app, confirm the derivation path matches to access the same addresses.

What happens if I enter a wrong word in my mnemonic?

The BIP39 checksum will fail validation, and a correctly implemented wallet will reject the phrase. This protects against a single transcription error producing a valid but unintended phrase. If your phrase fails validation, check spelling against the official word list — most errors are single-letter differences from the correct word.

Can I generate a BIP39 mnemonic in code?

Yes. Python: the mnemonic package (pip install mnemonic) from Trezor provides the reference implementation. JavaScript: @scure/bip39 (formerly bip39 from bitcoinjs). Go: github.com/tyler-smith/go-bip39. All implement the same RFC-compatible PBKDF2 seed derivation and the same 2,048-word list.