Developer Tools
BIP39 Mnemonic Generator
Generate a spec-compliant BIP39 mnemonic — 12, 18, or 24 words — using cryptographically secure randomness and a built-in checksum. Everything happens on your device: no server, no uploads, no keylogging risk.
Entropy
128-bit
Write this phrase on paper and store it offline. Anyone with your seed phrase controls your wallet. The phrase was generated on this device and never sent to any server.
Validate a phrase
What makes this tool different
Spec-compliant BIP39
Phrases use the official BIP39 English word list with a valid checksum word on every phrase.
Cryptographic randomness
Entropy comes from crypto.getRandomValues — the same secure source browsers use for encryption.
12 / 18 / 24 words
Choose 128, 192, or 256 bits of entropy to match your security requirements.
100% offline and private
Generation runs entirely in your browser. Your seed phrase never touches a server.
About this tool
BIP39 Mnemonic Generator: everything you need to know
A seed phrase is the master key of a cryptocurrency wallet — a human-readable sequence of words from which every address and private key is derived. Losing it means losing access forever; leaking it means losing the wallet. Generating it securely is the first and most important step, and the only truly safe place to do it is on your own device.
This BIP39 mnemonic generator creates phrases to the exact standard. It draws entropy from crypto.getRandomValues — the browser's cryptographic random source — then converts it into words from the official 2048-word English list, appending a SHA-256 checksum so the phrase is fully spec-compliant and verifiable by any BIP39 wallet.
You can choose 12, 18, or 24 words, corresponding to 128, 192, or 256 bits of entropy. For most personal wallets 12 words is secure; for larger holdings or long-term cold storage, 24 words gives the maximum margin the standard allows.
Because generation runs entirely in your browser, the phrase is never transmitted anywhere. No server logs it, no remote host can capture it, and there is no account tied to it. Open the DevTools Network tab and you will see zero requests.
What you do after generating matters as much as how you generate it. Write the phrase on paper or stamp it into metal, store it offline, and never enter it into any website. Hardware wallets and proper key-management practices build on top of this same BIP39 standard.
Verify your workflow before trusting it: generate a test phrase here, restore it in a BIP39-compatible wallet, and confirm the addresses match. The checksum means a mistyped word is caught immediately — a safety net that makes BIP39 phrases reliable to back up.
FAQ
BIP39 Mnemonic Generator — frequently asked questions
What is a BIP39 mnemonic / seed phrase?
A BIP39 mnemonic is a sequence of words — typically 12, 18, or 24 — generated from a random number according to the BIP39 standard. Wallets convert it into the seed that derives all your cryptocurrency keys, so the phrase is the single thing you must back up.
How does a 12-word vs 24-word seed phrase differ?
A 12-word phrase encodes 128 bits of entropy, an 18-word phrase 192 bits, and a 24-word phrase 256 bits. Both are considered cryptographically strong today; 24 words is the maximum the BIP39 standard supports and gives the largest safety margin.
What is the BIP39 word list?
It is the official list of 2048 English words defined by BIP39. Every mnemonic word must come from this list. The generator here uses the exact standard list, and the final word doubles as a checksum derived from your entropy.
Can I recover a wallet with my seed phrase?
Yes — that is the point. Any BIP39-compatible wallet lets you restore your keys by entering the phrase in order. This is why the phrase must be backed up securely and kept private; whoever has it controls the wallet.
How is the checksum word computed?
The standard takes your random entropy, hashes it with SHA-256, appends part of that hash to the entropy bits, then maps the combined bits into words from the 2048-word list. The last word therefore verifies the whole phrase.
Is generating a seed phrase in the browser safe?
Generating it locally with cryptographic randomness is safe because the phrase never leaves your device — this tool uses crypto.getRandomValues and makes no network requests. The risk comes after generation: never type the phrase into websites or share it, and store it offline.
How do I generate a BIP39 phrase in Python?
Use a library like mnemonic: from mnemonic import Mnemonic; m = Mnemonic('english'); print(m.generate(256)). You can verify any phrase here against the same BIP39 algorithm.
Is the BIP39 mnemonic generator free and private?
Yes. OpenToolLab's BIP39 generator is completely free, requires no signup, and generates phrases entirely in your browser — your seed never leaves your device.
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