Is it safe to type my seed phrase here?

The validation runs entirely in your browser using a local copy of the wordlist and the browser's built-in SHA-256. Nothing is sent over the network. That said, only ever do this on a trusted, malware-free device, and prefer an offline machine for a wallet that holds real funds.

What does the checksum actually verify?

BIP39 appends checksum bits derived from the SHA-256 hash of the entropy. The tool reverses the wordlist indices back into the entropy plus checksum bits, re-hashes the entropy, and confirms the checksum bits match. A wrong word or swapped order usually breaks it.

Why are only certain word counts allowed?

BIP39 phrases encode 128 to 256 bits of entropy in multiples of 32 bits, which produces exactly 12, 15, 18, 21, or 24 words. Any other count cannot be a valid BIP39 mnemonic, so the tool rejects it before checking the checksum.

A valid checksum means my phrase is correct, right?

It means the phrase is a structurally valid BIP39 mnemonic. It does not prove it is your phrase or that it controls a particular wallet. Many different valid phrases exist; the checksum only catches typos and ordering mistakes, not the wrong-but-valid phrase.

How many words could pass by chance?

The checksum is one bit per three words, so a random 12-word phrase of valid words has about a 1 in 16 chance of passing the checksum, and a 24-word phrase about 1 in 256. The check is a strong typo filter, not a guarantee of authenticity.

BIP39 Mnemonic Checksum Validator

A single mistyped or swapped word makes a recovery phrase useless. This validator checks every word against the official BIP39 wordlist and then verifies the checksum bits — all in your browser, so the phrase never leaves your device.

How it works

BIP39 packs entropy and a checksum into the word indices:

each word → its index (0-2047) → 11 bits
all bits   = entropy bits (ENT) + checksum bits (CS)
ENT        = words × 11 − CS,   where CS = ENT / 32

checksum   = first CS bits of SHA-256(entropy bytes)
phrase is valid if those bits equal the trailing CS bits of the phrase

So a 12-word phrase carries 128 entropy bits and 4 checksum bits; a 24-word phrase carries 256 entropy bits and 8 checksum bits. The SHA-256 step uses the browser’s native crypto, with no library and no network call.

Example and tips

If a phrase has 11 valid words and one not in the wordlist, the tool points at the offending word so you can fix the transcription. If all words are valid but two were swapped, the word check passes yet the checksum almost always fails, catching the ordering error. For any wallet holding real value, run this on an offline device and treat a passing result as “no typo detected,” not as proof the phrase is the right one.