What is the BIP 39 word list?

When a wallet shows you 12 or 24 words, it is not picking them at random from the dictionary. It is using a standard list called BIP 39 (Bitcoin Improvement Proposal 39). Most wallets, for bitcoin and many other networks, use it.

The list has 2,048 words. Each word stands for a number. Together, the words encode a big random number plus a small checksum, and that number is the starting point for all of your keys.

A few smart details:

• The first four letters are unique. In the English list, no two words share the same first four letters, so you can tell them apart even from a smudged note.
• The checksum catches some mistakes. If you type a wrong word, a wallet will often refuse the phrase. That does not catch every error, so write carefully.
• Order matters. The same words in a different order make a different wallet.

Knowing the list helps you spot fakes. If a “recovery tool” asks for your words, or a word you wrote down is not on the list, stop. And remember: the list is public, so the words alone are not the secret. Your exact words, in order, are.