What the validator checks
- Word count — BIP39 allows 12, 15, 18, 21 or 24 words.
- Wordlist — every word must be in the official English list of 2048 words. Unknown words are listed by position with close matches.
- Checksum — the words are turned back into bits, the entropy is hashed with SHA-256, and the result must match the checksum bits carried by the last word.
If the count or a word is wrong, the checksum is not evaluated, because it cannot be computed meaningfully.
Valid is not the same as safe
A valid mnemonic is simply well-formed. It does not tell you whether the phrase is the one you wrote down, whether anyone else has seen it, or whether a wallet uses a passphrase on top of it. A single wrong word can still produce a valid-looking phrase roughly one time in sixteen for 12 words (one time in 256 for 24 words).
Common reasons a phrase fails
- A misspelled word, such as
abandn. BIP39 words are unique in their first four letters, so the suggestion is usually right. - Swapped words. Order matters; swapping two words almost always breaks the checksum.
- A missing or extra word, giving an invalid count such as 11 or 13.
- A different wordlist or standard. Some wallets use other word lists or non-BIP39 schemes (for example Electrum seeds), which will not validate here.
How your input is handled
The text box is not part of a form, so it cannot be submitted into a URL. The input is not saved to storage, not logged, and not included in any analytics — this site has none. Validation runs only when you press the button, and the box is cleared when you leave the page. Clearing resets the page; like any web page, it cannot guarantee the browser has erased every copy from memory.