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BIP-39 Seed Phrase — Offline Working Sheet
Print this and follow it on paper. Do not write your words on this sheet if you plan to keep it anywhere insecure.
Pre-flight safety checklist
When using this for a real wallet, this computer will be disconnected from the internet (Wi-Fi off / airplane mode / ethernet unplugged) and will stay disconnected for the rest of that session.
I will write my final phrase down by hand on paper (or stamp it in metal) — never type, save, screenshot, photograph, email, or cloud-sync it anywhere.
I am in a private location where no one can see my screen, my dice/coin rolls, or what I write down.
Generating each word's 11 bits of randomness
Every word is a number from 0 to 2047. You need 11 of them for a 12-word phrase, or 23 for a 24-word phrase. The calculator works out the final word for you.
Method A — Coin flips or 11 dice (simplest, no bias, no rerolls)
Flip a fair coin 11 times for one word — or roll one die 11 times, or throw
11 dice at once and read them left to right in an order you fixed before throwing.
Write down Heads = 1, Tails = 0 (with dice, odd = 1, even = 0),
in the order you flipped or rolled.
You now have an 11-digit binary number, e.g. 01011010110.
Look that binary number up in the word reference table.
Repeat for every word.
Method B — Dice (5 six-sided dice per word)
Roll 5 dice. Subtract 1 from each face, so each die reads 0–5.
Combine them as a base-6 number: (d1 × 1296) + (d2 × 216) + (d3 × 36) + (d4 × 6) + d5
The result is somewhere in 0–7775.
If the result is 2048 or higher, discard it and reroll all 5 dice for that word. This happens just over 70% of the time — that is expected and correct, not an error. Do not try to "fix" a high number by subtracting or wrapping it; that would bias your entropy.
Once you have a number in 0–2047, look it up in the word reference table.
Repeat for every word.
The last word: the remaining bits
Your 11 or 23 words do not fill the phrase exactly. A few entropy bits are
left over, and the calculator will show you every word that could validly
finish the phrase — one row per possible value of those leftover bits.
Those bits are real entropy: generate them the same careful way, then use
the number as the row.
12-word phrase — 7 bits left over (rows 0–127)
Flip a coin 7 times. Heads = 1, Tails = 0, in order.
That 7-digit binary number is 0–127. Use it as the row number.
Dice alternative: 3 dice as a base-6 number
(d1 × 36) + (d2 × 6) + d3 gives 0–215.
Discard and reroll if it is 128 or higher (about 41% of rolls).
24-word phrase — 3 bits left over (rows 0–7)
Flip a coin 3 times. Heads = 1, Tails = 0, in order.
That 3-digit binary number is 0–7. Use it as the row number.
A single 8-sided die works too: roll it and subtract 1.
Never reduce a too-large roll with modulo, wrap it around, or simply
pick a row that looks good. Discard and reroll.
Roll tally
Tick off each word as you generate it. Write the numbers here if you must, never the finished phrase.
Free, independently created tool, provided as-is with no warranty and no liability.
Not affiliated with any wallet manufacturer, exchange, or the Bitcoin Improvement Proposals project.
Verify results independently before relying on this for anything of real value.
bip39toolbox.com
BIP-39 Offline Toolbox
Checksum calculator, phrase verifier, missing-word recovery and entropy converter —
all running locally in your browser, on words you generated yourself.
And why you can check it rather than trust it:
zero network requests, enforced by the browser ·
it refuses to run from a website ·
it re-proves its own arithmetic every time it loads ·
the whole source is one click away ·
nothing is stored but your light/dark preference ·
one button wipes every field, and an idle timer does it for you ·
the print sheet never contains your words.
Before you use this with a real wallet:
Disconnect from the internet (turn off Wi-Fi / airplane mode) before typing any real words into this page. Ideally run this on an offline or air-gapped computer.
This file makes zero network requests — the entire word list and all math are embedded below and run only in your browser. You can verify this yourself by opening the file in a text editor.
Never paste your words in a chat, an online tool, cloud storage, or any internet-connected app.
Test this tool first with throwaway/fake words and cross-check the result against another independent offline tool before trusting it with a real seed.
When you're done, close this tab and clear your browser history for this page if the computer isn't fully offline.
Opens the whole source in a separate window, so you can see for yourself that there
is no network call in it. This is for reading, not verifying — a tampered
file would show you its tampered code just as happily. Checking the hash is what
proves the file is genuine.
⌛
Running self-test…
Re-proving the checksum math in your browser.
File integrity self-check
SHA-256 of this page as loaded: computing…
Verifying this file wasn't tampered with, if it was given to you by a third person
and not downloaded directly from bip39toolbox.com
Did someone give you this file? If it reached you as an email attachment, a chat
message, a USB stick or a shared folder — anything other than you going to
bip39toolbox.com and downloading it yourself — then check
it before you type a real seed phrase into it. A single altered character could silently
hand your phrase to someone else.
For the best security, download it yourself from
bip39toolbox.com. That is the recommended way to get this
file, and it is the one case where an extra check is least likely to be needed. A copy
that passed through someone else's hands is where it matters most.
Opens the step-by-step instructions in a separate window. Everything runs on this machine;
nothing is sent anywhere.
Verifying this file wasn't tampered with
A single altered character in this file could silently hand your seed phrase to
someone else. Checking the hash is how you catch that — but only if you
check it the right way.
Where the hash comes from. The authoritative hash for this file is published at
bip39toolbox.com/hash — deliberately on a different page
from the download itself. Navigate to that address yourself. Do not follow a link that
arrived alongside the file.
Every copy is worth checking, including one downloaded from that site. If you are
obtaining this file for the first time, downloading it from the official site is better
provenance than accepting a copy from someone else — but it is not a substitute for
the check, and it is the weaker of the two cases:
Downloaded from the site, checked against that site's hash. Catches a corrupted
transfer or a swapped mirror. It cannot catch a compromised host: whoever replaced the
download could replace the published hash too.
Received some other way — email, USB, a friend — and checked against the
hash on the site you went to yourself. The strong case. An attacker would have to
compromise both channels to stay hidden.
1. Compute this file's hash yourself
You need a terminal open in the folder where this file is saved. If you
have never done that, here is how:
You'll get a 64-character hexadecimal string. That is this exact file's fingerprint:
change one byte anywhere in it and the fingerprint changes completely.
2. Compare it against a hash that arrived separately
The comparison is only meaningful if the hash reached you through a
different channel than the file did. If the file came as an email
attachment, get the hash by text message, phone call, printed note, or from a
separate website you navigated to yourself.
Why this matters: if the hash sits right next to the file — same
email, same download page, same chat message — then anyone who could
tamper with the file could just as easily edit the hash printed beside it to
match their modified version. The two would agree perfectly and you'd have
verified nothing. Two channels means an attacker has to compromise both to
stay hidden, which is a far higher bar than compromising one.
Sixty-four characters is more than the eye reliably checks — and anyone who
tampered with the file would make the first and last few match on purpose. Have the
computer compare instead, pasting in the hash that reached you separately:
macOSecho "PASTE_THE_HASH_YOU_RECEIVED bip39_checksum_calculator.html" | shasum -a 256 -c
macOS and Linux print bip39_checksum_calculator.html: OK;
Windows prints True. Any other result is a mismatch.
3. If you pass this file on to someone else
The same rule applies in reverse, and it is your responsibility to follow it:
send the file and its hash through two different channels, never the same
one. Emailing someone the file with the hash pasted underneath gives them
no protection at all. Send the file however is convenient, then send the hash
a different way — a text, a call, in person, on paper.
If the hashes don't match, stop. Do not enter a real seed phrase into
this file. A mismatch means the file is not the one that was published —
it may have been corrupted in transit, or it may have been deliberately
modified. Either way, treat it as untrusted until you have resolved exactly
why the two values differ.
Save a copy of this file
This copy will not match the published hash. Your browser cannot read its own
file off the disk, so the button below rebuilds the page from what is currently in
memory. That rebuild is a faithful, working calculator, but it is not byte-for-byte
identical to the original — whitespace and attribute order shift — so its
SHA-256 comes out different.
Do not hand this copy to anyone else as the official file. They will check it
against the published hash, it will not match, and they will correctly conclude it was
altered. To pass the real file on, copy the actual file with Finder, File Explorer or
onto a USB stick — and send the hash by a separate channel.
This button is for one thing: keeping a spare for yourself on a machine where the file
manager is awkward to reach. The copy calculates correctly and re-runs its own load-time
self-test, so it is safe to use; it just cannot be vouched for.
BIP-39 Offline Toolbox
A seed phrase checksum calculator, verifier, missing-word recovery tool and entropy
converter in one HTML file — running entirely on your own machine, with the network off. No accounts, no server, no dependencies,
nothing to install. Free, and small enough to read in a text editor.
🔒 This calculator only runs when opened as a local file
You are viewing this page over the internet (),
and the calculator is switched off. That is deliberate: typing a real seed phrase into any
page served by a website means trusting the server, the connection and everyone in between.
Download the file and open it from your own disk, and there is nothing left to trust but
the file itself — which you can read.
Download the file with the button below
When using it for a real wallet, disconnect the device from the internet
Double-click the downloaded file — it opens in your browser from disk, not from a website
The calculator unlocks by itself once it sees it is running locally
What it does
Safety first
When you are working on a real wallet, the program runs offline, on your own
computer — not on a website, not on anyone's server. Disconnect the machine,
open the file from your disk, and nothing you type can leave the room.
Generate
Enter the 11 or 23 words you produced with your own dice or coins and it works out the last
word that completes the phrase — your 12th word, or your 24th. That final
word is not free: it carries the checksum, so only certain words fit. The tool lists every
one of them — 128 for a 12-word phrase, 8 for a 24-word one — for you to choose
between with your own dice. It never invents randomness; the entropy is yours.
Verify
Check a phrase you already have. If the checksum fails it does not just say "invalid":
it points at which word is most likely wrong, suggests near-misses, and spots two adjacent
words in the wrong order.
Recover a missing word
One word smudged or torn? Leave that box blank — anywhere in the phrase — and
it finds every word that fits the checksum. Type any fragment you can still read and it
usually narrows to one.
Convert either way
Raw entropy to phrase, or phrase back to entropy, as hex or binary, with every word's
index and 11-bit value shown. Useful for cross-checking this tool against another one.
Dice calculators — no maths
Three physical methods, each with a calculator: coin flips or 11 dice, five dice in
base-6, or a d6 plus three d10 rolls. Type the faces exactly as they landed and it works
out the index for you, showing every step so you can check it by hand if you want to.
Every accept rule is proved uniform by enumerating all possible rolls.
The full BIP-39 table
All 2048 words with their index and 11-bit binary, searchable by word, by number, or by
pasting an 11-digit binary string straight in. The same table the calculator itself uses,
not a separate copy that could drift.
Yours to keep
One file, 362 KB, nothing to install and nothing that ever needs updating. Download
it once and it keeps working — offline, on an air-gapped laptop, from a USB stick,
years from now, whether or not this site still exists.
Ten languages
All ten official BIP-39 word lists — English, Spanish, French, Italian, Portuguese,
Czech, Japanese, Korean and both Chinese. English always loads by default.
Why you can check it rather than trust it
Zero network requests. Not "few" — none. The file contains no
fetch, no XMLHttpRequest and no
WebSocket call anywhere, and a Content-Security-Policy of
default-src 'none' with no connect-src
blocks every outbound connection at the browser level regardless.
It refuses to run from a website. You are looking at that refusal right now.
It proves its own arithmetic on load. Both BIP-39 reference vectors are recomputed,
and its from-scratch SHA-256 is cross-checked against your browser's own implementation
across a spread of block boundaries. A mismatch locks the tool rather than warning you.
You can read the code without leaving the page. A button opens the whole source in
a window — search it for fetch yourself.
Nothing is stored. No cookies, no trackers, no server logs, no counters,
nothing in local storage but your light/dark preference.
It cleans up after itself. One button wipes every field and verifies they are
empty; an idle timer does the same if you walk away.
The print sheet never contains your words — only the checklist and the dice guide.
No install, no updates, no expiry. It is one file. Nothing phones home to check a
version, nothing stops working when a service is retired, and a copy on a USB stick in a
drawer will still run in ten years.
Check the download before you trust it
Downloading from here is better than accepting a copy from someone else, but it is not a
substitute for checking. Compute the file's SHA-256 after downloading and compare it against
the hash published at bip39toolbox.com/hash — deliberately a different page
from this one, so that replacing the download would not be enough to fool the check. The
file explains exactly how, for each operating system, once you open it.
Free, independently created, provided as-is with no warranty and no liability. Not affiliated
with any wallet manufacturer, exchange, or the Bitcoin Improvement Proposals project. Verify
results independently before relying on this for anything of real value. The full disclaimer
is in the file.
Before you begin — required checklist
The tool below stays locked until all three are checked.
Prints the checklist and the dice/coin guide only — never any words you have entered.
Disclaimer
This is a free, independently created tool, provided as-is and free of charge, with no warranty of any kind,
express or implied. It is not affiliated with, endorsed by, or supported by any wallet manufacturer, exchange,
or the Bitcoin Improvement Proposals project. You use this software entirely at your own risk. The creator(s)
of this tool accept no responsibility and no liability whatsoever for any loss of funds, loss of access to a
wallet, loss of data, or any other direct, indirect, incidental, or consequential damages arising from the
use, misuse, or inability to use this software — including but not limited to software errors, user
error, hardware failure, or the loss, theft, or exposure of a written seed phrase. Always independently verify
results (see the "Word list source & integrity" section above) before relying on this tool for anything
of real value.