BIP-39 Mnemonic Phrase Generator

A crypto wallet’s seed phrase looks like twelve or twenty-four ordinary words, but the ordering encodes both randomness and a checksum, and getting either wrong produces a phrase that looks fine and restores nothing. BIP-39 Mnemonic Phrase Generator builds one the way the specification defines it: real entropy from crypto.getRandomValues, a SHA-256 checksum appended to it, the combined bits sliced into 11-bit chunks, and each chunk mapped onto the official 2048-word list.

It exists for testing, not for holding funds: trying a wallet library against a known phrase, teaching someone what a seed phrase actually is before they trust one, or generating throwaway test fixtures for an app that consumes them. Pick a word count, and a phrase is ready immediately.

Getting Your First Phrase Generated

1. Choose an Entropy Strength — 12 words for 128 bits, up to 24 words for 256 bits. A phrase appears the moment you land on the page.
2. Click Reveal to un-blur the grid, or leave it hidden and click Copy anyway — copying works without ever showing the words on screen.
3. Click Generate New Phrase for a fresh one at the same word count.

How the Math Behind the Checksum Works

For a strength of ENT bits, the checksum is the first ENT/32 bits of SHA-256(entropy) — 4 bits for a 12-word phrase, 8 bits for a 24-word one. Appending that to the entropy and slicing the result into 11-bit groups is what keeps a mistyped or corrupted word from silently passing as valid elsewhere: change one bit and the checksum almost never still matches. This implementation was checked against the reference BIP-39 test vectors during development, including the well-known all-zero case that must produce “abandon” repeated eleven times followed by about, and it matches exactly.

When Not to Use This for a Real Wallet

“For learning, testing and development only. Never fund a wallet with a phrase generated in a browser tab” is printed on the tool itself, not buried in a footnote, because the failure mode here is expensive. A browser tab can be closed, crashed, or run on a compromised machine, and none of that is something a hardware wallet or an offline generator has to worry about. Nothing typed or generated here is transmitted anywhere, but “never transmitted” is not the same guarantee as “generated on a device that has never touched the internet,” which is what real funds deserve.