BIP39 Checksum Checker

What the checker tells you

• Words that are not in the list, each with up to three likely corrections: words with the same first four letters, or words one or two letters away. In the English list the first four letters identify every word, so "abso" can only be "absorb".
• Whether the length is valid. BIP39 phrases have 12, 15, 18, 21 or 24 words. 20 or 33 words point to a SLIP-39 share, 25 words to a Monero phrase.
• Whether the checksum matches, once every word is known and the length is right.
• Whether the words are an Electrum seed. Electrum has its own format, in which an HMAC-SHA512 of the phrase starts with a version number; current Electrum versions make such phrases fail the BIP39 check on purpose.

How the BIP39 checksum works

A BIP39 phrase encodes a random number, the entropy, plus a few check bits. The wallet hashes the entropy with SHA-256 and appends the first ENT/32 bits of the hash, where ENT is the entropy length. The combined bits are cut into groups of 11, and each group picks one of the 2048 words, so the checksum always sits in the last word.

To check a phrase, the tool turns the words back into numbers, splits off the last ENT/32 bits, hashes the rest and compares. The same check runs when you restore a wallet, which is why a typo usually produces an "invalid mnemonic" error instead of an empty wallet. The method is defined in the BIP39 specification; this page uses the same @scure/bip39 library as the site's other tools.

When a phrase fails

Most failures come from writing the phrase down, not from the wallet. In order of likelihood:

1. A misspelled word. The checker flags it and suggests corrections; the full BIP39 word list lets you compare letter by letter.
2. A word misread as another valid word, such as wave and wage. Both are in the list, so only the checksum notices.
3. Two swapped words, often in a phrase copied in columns.
4. A phrase that is not BIP39: Electrum seeds, SLIP-39 shares, Monero phrases, or TON's 24-word format, which uses BIP39 words but its own check.

Our guide on how to fix seed phrase errors walks through each case, including how many combinations a missing word leaves.

Related tools

Building a phrase from dice or coin flips? The BIP39 last word calculator lists every word that completes it. To see the keys and addresses a test phrase produces, use the seed phrase to private key converter, and to create a random phrase, the BIP39 generator.