BIP-39 Mnemonic Tool

Features

• Generate 12 / 15 / 18 / 21 / 24 words (128–256 bits of entropy)
• Both official wordlists — English and Simplified Chinese — never mixed
• Word indices are shown so you can check a phrase word by word
• Validate checks the word count, the wordlist and the checksum
• Seed derivation via PBKDF2-HMAC-SHA512, 2048 rounds, 64 bytes
• The passphrase may be empty, and empty is kept distinct from any other
• Randomness comes from crypto.getRandomValues and can be injected for tests
• Copy a single row, or all of them

How to use

1. Pick Generate, Validate or To seed
2. Choose entropy bits and wordlist, or paste the phrase into the input
3. Results appear at once: entropy, indices, or the seed
4. Use the copy button on a row to take just that value

FAQ

Is it safe to type my mnemonic into a web page?

All computation happens locally in your browser; the page sends no requests and there is no server to receive anything. But the page itself came from the network and you cannot verify it was not altered — so do not paste the mnemonic of a wallet you actually use. This tool is for checking a phrase you were given, or generating expected values in tests.

What is the checksum, and why does one wrong word break it?

The last few bits of the phrase (4–8 of them) are a copy of the leading bits of SHA-256 over the entropy, so a transcription error shows up. If the word count and wordlist are fine but the last word is swapped, the phrase is no longer a valid encoding of any entropy — wallets reject it, or derive a private key entirely different from the one you expected.

What difference does a passphrase make?

The same mnemonic with different passphrases yields completely different seeds — that is BIP-39's extension mechanism (the "25th word"). An empty passphrase is a valid one, but it differs from every non-empty passphrase, and a lost passphrase means the seed can never be re-derived.

Does a Chinese mnemonic need spaces?

No. Every Chinese wordlist entry is a single character, so the tool splits it per character; English words must be separated by spaces.