Generate BIP39 mnemonic seed phrases (12–24 words) and validate existing ones against the standard wordlist and checksum. Runs entirely in your browser — never paste a real wallet's seed phrase into any website.
A failed check tells you why: which words aren't in the BIP39 wordlist and what they were probably meant to be, or that every word is real but the checksum doesn't match. Where a single word is misspelled, the checksum usually narrows the correction to one candidate — how that works.