BIP39 seed phrase checker
Never type a seed phrase that holds real money into any website, including this one. Anyone who sees those words owns the coins. Use this page with practice phrases, or save it and open it on a computer that's offline.
Practice phrases are for learning. Make the phrase for real money on your own wallet or hardware device.
Last word calculator
Typed 11 or 23 words? Only some words can come last, because the last word carries the checksum. They're listed below the checker when you enter 11, 14, 17, 20 or 23 words.
How the checksum works
Each word stands for 11 bits. A 12-word phrase is 132 bits: 128 bits of random entropy plus a 4-bit checksum taken from the SHA-256 hash of that entropy. That's why about 1 in 16 random 12-word lists is valid, and why a typo usually gets caught.
The 2,048 English words come from the official BIP39 list. They're built into this page, so nothing is loaded or sent while you type. The page's security policy blocks all network requests from its code.