BIP39 Offline Tools
Version 0.1.0. Everything runs inside this file; network connections are blocked by its Content Security Policy.
This device appears to be online. Disconnect from the network before entering a real recovery phrase.
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- Entropy
- 128 bits
- Checksum
- 4 bits
- Words
- 12
- Language
- English
Other wordlist languages are planned, not yet available.
The official English test vectors cover 12, 18 and 24 words only.
Secure randomness (crypto.getRandomValues) is unavailable in this browser, so generation is disabled. Test vectors still work.
Mnemonics generated on a website are for testing and learning. For a wallet that will hold funds, use a hardware wallet or the offline tool on a disconnected device.Generate real phrases only on a trusted device with networking turned off. For significant funds, prefer a hardware wallet.
Anything you copy can be read by other apps with clipboard access.
Next: see how the checksum is built · validate a mnemonic · derive the seed
Use test data only. For a real recovery phrase, use the offline tool.Keep this device disconnected while entering a real phrase. Close the browser when done.
Checks run only when you press Validate (or Ctrl/⌘ + Enter).
Entropy to mnemonic
Encode 128–256 bits of hex entropy (32, 40, 48, 56 or 64 hex characters) as BIP39 words.
Use test data only. For a real recovery phrase, use the offline tool.Keep this device disconnected while entering a real phrase. Close the browser when done.
Mnemonic to entropy
Decode a mnemonic back to its original entropy. The checksum must be valid.
Use test data only. For a real recovery phrase, use the offline tool.Keep this device disconnected while entering a real phrase. Close the browser when done.
Mnemonic to seed
Derive the 512-bit BIP39 seed with PBKDF2-HMAC-SHA512 (2048 iterations, salt "mnemonic" + passphrase). No private keys or addresses are shown.
Use test data only. For a real recovery phrase, use the offline tool.Keep this device disconnected while entering a real phrase. Close the browser when done.
- Fingerprint
- Passphrase
Fingerprint = first 8 hex characters of SHA-256(seed), for comparing seeds at a glance.
Source: Test vector #1 This page never asks for your own mnemonic.
Entropy: 128 random bits
Hex0000000000000000000000000000000000000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000Explain
BIP39 starts from 128 bits of entropy (ENT). Allowed sizes are 128 to 256 bits in steps of 32. Here the 32 hex characters are shown as 128 bits, 8 per byte.
Hash the entropy with SHA-256
SHA-256(entropy)374708fff7719dd5979ec875d56cd2286f6d3cf7ec317a3b25632aab28ec37bbFirst 4 bits of the hash: 0011 → checksum
0011Explain
The checksum length is CS = ENT / 32 = 128 / 32 = 4 bits. They are the first 4 bits of the SHA-256 hash of the raw entropy bytes (not of the hex text).
Append the 4 checksum bits
00000000000 00000000000 00000000000 00000000000 00000000000 00000000000 00000000000 00000000000 00000000000 00000000000 00000000000 00000000011Entropy (128 bits)Checksum (4 bits)
Explain
Entropy + checksum = 128 + 4 = 132 bits, which divides exactly into 11-bit groups: (ENT + CS) / 11 = 12 words.
Split into 12 groups of 11 bits
Explain
Each 11-bit group is a number from 0 to 2047 — an index into the 2048-word list. Only the last group contains checksum bits, which is why the last word cannot be chosen freely.
Map each index to a word
Mnemonic · 12 words- 01abandon
- 02abandon
- 03abandon
- 04abandon
- 05abandon
- 06abandon
- 07abandon
- 08abandon
- 09abandon
- 10abandon
- 11abandon
- 12about
Explain
Index 0 is
abandonand index 2047 iszoo. The words are joined with a single space to form the mnemonic.
Showing all 2048 words. Numbers are 1–2048; the 11-bit index is 0–2047. Click a word to copy it.
Skip the word listBIP39.ai offline 0.1.0 · commit 211d6ed · MIT License · Specification: bitcoin/bips BIP-0039. Verify this file against the SHA-256 published at https://bip39.ai/bip39-offline/