BIP39 Mnemonic Generator and Validator
Generate and validate BIP39 mnemonic seed phrases of 12 to 24 words, with crypto-strong randomness and full checksum checking. Free, in your browser.
For a wallet holding real value, generate your seed phrase offline on a trusted, air-gapped device. This runs client-side and nothing is uploaded, but a browser is not a hardware wallet. Use this for development, testing and learning.
Pick a length and click Generate to create a fresh BIP39 phrase.
Editable — paste a known entropy and the phrase it defines appears above.
Paste a phrase above — extra spaces, line breaks and capitalization are fine.
🔒 Phrases are generated and checked entirely in your browser with a cryptographically-strong RNG (WebCrypto). Nothing is ever uploaded.
What a BIP39 mnemonic is
A BIP39 mnemonic is a human-readable seed phrase — 12, 15, 18, 21, or 24 words drawn from a fixed 2048-word wordlist — English by default, with nine other languages to pick from — that encodes the random entropy behind a crypto wallet. The tool turns 128 to 256 bits of entropy into words and appends a short SHA-256 checksum, so a single mistyped or reordered word makes the phrase fail validation. Every extra three words add 32 bits of entropy: 12 words carry 128 bits and 24 words carry 256 bits.
Generate and validate phrases locally
Pick a length and click Generate to produce a fresh phrase using the audited @scure/bip39 library and your browser's cryptographically-strong random number generator (WebCrypto) — never Math.random. Paste any phrase into the validator to confirm its words, length, and checksum are correct and to read the raw entropy in hex. Everything runs client-side and nothing is ever uploaded. Still, a browser tab is not an air-gapped hardware wallet: for a wallet that will hold real value, generate your seed offline on a trusted device. Use this tool for development, testing, and learning.
Frequently asked questions
Is it safe to generate a real wallet seed here?
Treat it as a developer and learning tool, not a hardware wallet. Generation runs entirely in your browser with a cryptographically-strong RNG and nothing is uploaded, but a general-purpose browser is not air-gapped. For funds of real value, generate your seed phrase offline on a trusted, dedicated device.
What is the difference between 12 and 24 words?
The word count sets the entropy: 12 words is 128 bits, 15 is 160, 18 is 192, 21 is 224, and 24 is 256 bits. More words mean a larger security margin, and 12 and 24 words are the most common choices.
Why does my phrase show as invalid?
A BIP39 phrase is invalid if any word is not in the wordlist you have selected, if the word count is not 12, 15, 18, 21, or 24, or if the built-in checksum does not match. The validator ignores extra spaces, line breaks, and capitalization, so those never cause a failure.