Randomness you can watch happen
When a wallet makes a seed for you, you have to trust that its random number generator did its job, and you have no way to check. Coins are different. You see every flip land. These tables turn those flips into BIP-39 words and passphrase characters.
A seed is only as strong as the randomness behind it. If a bug makes a wallet use predictable randomness instead of real randomness, you cannot tell from the outside. The screen still shows you twelve normal looking words. Making the randomness yourself removes that problem completely, and it costs you an afternoon.
The safest way to use this page is not to use it on a screen at all. Print it, or save it and open it on a computer with the internet switched off. Then looking up your words never touches a browser that is online. Section 04 explains why that is worth doing.
Use eleven coins of the same kind. Heads counts as 1 and tails counts as 0. Once you let them out, read them across from left to right, and that is your eleven digits.
If you would rather not depend on where they land, use eleven coins of different sizes instead, and decide before you start which size is which digit. Write that down. Then you can read them in the same order every time, however they scatter.
Put them in a box with a lid. The box needs to be big enough that the coins can tumble freely, not a tight tin where they only slide. Shake it hard, then let them out onto the floor or a table. Do not flip them and catch them in your hand. A caught coin tends to land the same side up that it started with, about 51 times in 100, because it wobbles in the air instead of spinning cleanly. Letting them bounce on the floor avoids that. If any are stacked or too close to read cleanly, put them back and shake again.
Eleven coins give you one of 2048 results, and there are exactly 2048 BIP-39 words. So one throw is one word. The order below comes from the BIP-39 standard itself, where a word’s position in the list is its number. This is not something we invented, and every wallet uses the same list.
The last word is the one you cannot pick freely. Part of it is a check code that has to match all the words before it, so your wallet works it out for you. For a 24 word seed, flip the first 23 words and your wallet will offer 8 possible last words, so flip 3 more coins to choose between them. For a 12 word seed, flip the first 11 words and your wallet will offer 128 endings, so flip 7 more coins to pick one.
Only the first four letters are shown bright, and those are the only ones you punch on the steel plate. No two words in the list start with the same four letters, so four is always enough to tell them apart. 103 of the words are only three letters long, and those have nothing dimmed because the whole word is already short enough.
Words are shown in capitals to match the way an ImpactPlate is marked. The official BIP-39 list is lowercase, but that never causes a problem. Hardware wallets have you pick words from a list instead of typing them, and phone and desktop wallets change what you type to lowercase anyway.
Six coins give you one of 64 results, and this alphabet has exactly 64 characters, so every throw makes one character and no flips are wasted. Twenty-two is stronger than 12 BIP-39 words. Even someone who already had your seed words could not guess a passphrase that long.
When you are done, glance at what you got. If there is no digit and no symbol, flip a few more characters and append or replace until there is at least one of each, or reroll the whole thing. At 22 characters you will almost never need to. Do not force a scheme like “first character must be a digit.” That costs entropy and clarity for a problem that length already solves.
The alphabet leaves out 0, O, o, 1, l and I, so nothing in it can be mistaken for something else. A few pairs still look similar, like 5 and S, 2 and Z, or 8 and B. Check that whatever you write or stamp it with makes those clearly different before you commit to anything permanent.
ImpactPlate is for your seed words. We do not make a passphrase plate for now, and your passphrase should not go on the same piece of metal as your seed anyway. Keeping both halves of the secret in one place defeats the point of having a passphrase at all. Store it somewhere separate.
Wherever you store it, note that this alphabet uses both capital and small letters. Most metal stamp sets only have capitals, and in that case they usually provide an underscore so you can differentiate between them.
Check what your device accepts before you start. Coldcard and Ledger both take up to 100 characters. Trezor stops at 50. Also write down the wallet fingerprint that your passphrase produces. A wrong passphrase does not show an error, it just opens a different empty wallet, so the fingerprint is a quick way to check you typed it right.
The obvious thing to add here is a box where you type your eleven flips and get the word back. We are not going to add one. Here is why, so you know it was a decision and not something we forgot.
A search box gets you used to typing seed words into a browser, and that habit is the real danger. Maybe not on this page, but on the next site that looks like this one and is run by someone you cannot identify. Anything you type into a web page can be read by browser add-ons, saved by form history, and left behind in crash files long after you close the tab.
Typing is not the only way to give something away. A page can also watch where your mouse goes, what you hover over, and what text you select. If you highlight each word as you find it, that trail is every bit as revealing as typing the words in. You do not have to type anything for a page to learn what you were looking at.
We also cannot prove to you that any of this is safe. A page that behaves perfectly today could be changed tomorrow by anyone who can update the site, and you would have no way of knowing. Asking you to trust a promise is worse than simply not building the thing that needs trusting.
So the table just sits there. There is no search box and no place to type your flips or words. That is the point. The trade off is a little more looking, and the words are grouped so that looking is not hard.