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BIP39 Mnemonic Generator - Online 12/24 Words

Generator Security BIP39 mnemonic seed wallet
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Cryptographically Secure

BIP39 Mnemonic Generator

Generate cryptographically secure BIP39 mnemonic phrases with 12 or 24 words. All computation happens locally in your browser — nothing is ever sent to any server.

Security Strength
Very Strong
Click "Generate New" to create your first mnemonic
Important Security Reminders
  • Never share your mnemonic phrase with anyone — it grants full access to your wallet.
  • Store your mnemonic offline (paper, metal backup) in a secure location.
  • This tool runs entirely in your browser. No data is transmitted or stored.
  • For maximum security, use this tool on an air-gapped (offline) device.
  • Consider using a hardware wallet for storing significant crypto assets.

Frequently Asked Questions

Everything you need to know about BIP39 mnemonic phrases

BIP39 (Bitcoin Improvement Proposal 39) defines a standard method for generating human-readable mnemonic phrases from random entropy. These phrases serve as a backup for cryptocurrency wallets — allowing you to recover your private keys and funds if your device is lost or damaged. The standard uses a carefully selected list of 2,048 English words, where each word represents 11 bits of data.
A 12-word mnemonic encodes 128 bits of entropy (plus 4 bits of checksum), providing 2128 possible combinations — already computationally infeasible to brute-force with current technology. A 24-word mnemonic encodes 256 bits of entropy (plus 8 bits of checksum), offering 2256 combinations. While 24 words provide even stronger theoretical security, 12 words are considered more than sufficient for everyday use and are easier to back up.
Yes. This tool uses the Web Crypto API (crypto.getRandomValues) — the same cryptographically secure random number generator used by modern browsers for security-critical operations. All computation happens locally on your device; your mnemonic is never transmitted to any server. For maximum security, you can download this page and run it offline, or use it on an air-gapped computer.
Most major wallets support BIP39 mnemonics, including hardware wallets (Ledger, Trezor), software wallets (MetaMask, Trust Wallet, Exodus, Electrum), and mobile wallets. The BIP39 standard is widely adopted across the cryptocurrency ecosystem. Always verify that your specific wallet supports BIP39 before importing.
Best practices include: writing the phrase on paper and storing it in a fireproof safe; using metal backup solutions (stamped steel plates) for fire and water resistance; storing multiple copies in geographically separate secure locations; never storing it digitally (no photos, cloud storage, or password managers); and never sharing it with anyone. Consider using a passphrase ("25th word") for additional security.
2,048 = 211, meaning each word encodes exactly 11 bits of data. This makes the encoding mathematically elegant: for a 12-word mnemonic, 12 × 11 = 132 bits total (128 bits entropy + 4 bits checksum). The word list was carefully chosen to include distinct, easily distinguishable words with no ambiguous spellings across different English dialects.
The checksum is a short digest derived from the entropy using SHA-256. It's appended to the entropy before splitting into 11-bit word indices. For 12-word mnemonics, the checksum is 4 bits (entropy_length / 32); for 24-word mnemonics, it's 8 bits. The checksum allows wallets to detect typing errors when recovering from a mnemonic — if the checksum doesn't match, the phrase is invalid.
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