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BIP-39 Mnemonic Generator

100% Free

Generate real BIP-39 recovery phrases (12, 15, 18, 21, or 24 words) using cryptographically secure entropy and the official wordlist — plus a checksum validator to sanity-check a phrase you already wrote down. Educational and testing use; never enter a real wallet's seed phrase anywhere.

Real BIP-39 Spec
12–24 Words
100% Client-Side
⚠ Never type a real wallet's recovery phrase into any website. Use this tool only to learn the BIP-39 format, generate a brand-new test phrase, or sanity-check the checksum of a phrase you already wrote down — everything runs locally in your browser and nothing is ever sent anywhere.

Your Recovery Phrase

Generating cryptographically secure entropy…

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How to Use

  1. 1 Pick a word count — 12 words (128-bit entropy) is the most common default used by wallets like Bitcoin Core and most hardware wallets.
  2. 2 Click Generate New Mnemonic. Fresh entropy is drawn from your browser's crypto.getRandomValues, hashed with SHA-256, and split into the word list per the BIP-39 spec.
  3. 3 Copy the phrase if you need it for a test wallet, a tutorial, or to study the format — never for a real wallet you intend to fund.
  4. 4 To check a phrase you already have, switch to the Validate Mnemonic tab, paste it in, and the tool recomputes its checksum to confirm it's well-formed.

Features

  • Implements the real BIP-39 algorithm — entropy → SHA-256 checksum → 11-bit word groups — not a fake or simplified lookup
  • Supports all 5 official word counts: 12, 15, 18, 21, and 24 words (128 to 256 bits of entropy)
  • Uses the official 2,048-word English BIP-39 wordlist, in its exact specified order
  • Built-in checksum validator — paste any 12/15/18/21/24-word phrase to confirm it's well-formed
  • 100% client-side: entropy generation, hashing, and word lookup all happen in your browser
  • No sign-up, no analytics on the phrase content, no server round-trip of any kind

Why it Matters

BIP-39 is the standard that turns a wallet's random private-key entropy into a human-writable, human-checkable sequence of words — almost every modern crypto wallet uses it. Understanding exactly how a seed phrase is built (and how its checksum catches a single mistyped or misheard word) is valuable for anyone learning wallet security, building wallet software, or writing test fixtures. This tool implements the actual spec rather than a toy approximation, so the output matches what a real wallet would produce from the same entropy — while keeping a loud, persistent reminder that a phrase tied to real funds should never touch a web page.

★★★★★

Use Cases

Wallet Developers & QA

Generate valid test mnemonics and known entropy/phrase pairs for unit tests, demos, and onboarding flows — without risking a real seed.

Learning the BIP-39 Spec

See exactly how entropy, a SHA-256 checksum, and the 11-bit word groups combine to produce a recovery phrase.

Checksum Sanity-Check

Paste a phrase you wrote down by hand to confirm every word and the checksum are intact, before you find out the hard way.

Tutorials & Talks

Generate a fresh, throwaway example phrase live for a workshop or blog post instead of reusing a stale, possibly-memorized example.

What this tool does

The BIP-39 Mnemonic Generator implements the actual BIP-39 specification used by real crypto wallets: it draws cryptographically secure entropy, hashes it with SHA-256 to derive checksum bits, and maps the combined bit string onto words from the official 2,048-word English list. A built-in Validate Mnemonic tab does the reverse — paste a phrase and the tool recomputes its checksum to confirm every word and the word order are correct.

⚠ A word on safety

This tool is for learning, development, and testing — generating throwaway example phrases, building test fixtures, or double-checking the checksum of a phrase you already control. Never type a real wallet’s recovery phrase into this or any other website. A genuine seed phrase should be written on paper and entered only into the wallet software itself; even a tool that’s honestly 100% client-side (like this one) is the wrong place for key material you can’t independently verify wasn’t intercepted by something else running on the device.

How the algorithm works

  1. Entropy. Generate 128–256 bits of random bytes (16–32 bytes), depending on the chosen word count, using crypto.getRandomValues.
  2. Checksum. Hash the entropy with SHA-256 and take its first entropy_bits / 32 bits as a checksum.
  3. Word groups. Append the checksum to the entropy and split the result into 11-bit chunks — each chunk is an index (0–2047) into the wordlist.
  4. Mnemonic. Join the looked-up words with spaces to form the final phrase.

Validation reverses the process: split the phrase back into 11-bit indices, separate entropy bits from checksum bits, re-hash the entropy, and compare checksums.

Privacy

Entropy generation, SHA-256 hashing, and every word lookup happen entirely inside your browser. Nothing about a generated or validated phrase is transmitted, logged, or stored anywhere by this site.

Frequently Asked Questions

What is a BIP-39 mnemonic phrase?
BIP-39 (Bitcoin Improvement Proposal 39) defines a standard for converting a wallet's random binary entropy into a sequence of common English words — 12 to 24 of them — that's much easier for a person to write down, read back, and re-enter correctly than raw hexadecimal. Almost all modern crypto wallets (Bitcoin, Ethereum, and most others) use BIP-39 mnemonics as the human-readable form of a wallet's master seed.
Is this tool safe to use for a real wallet's seed phrase?
No — and this tool is built specifically so you don't have to make that choice. Use it to generate a brand-new throwaway phrase for learning or testing, or to validate a freshly-generated test phrase. A real wallet's recovery phrase should be written down on paper, never typed into any website, browser extension, or app other than the wallet software itself — even an honest, offline-only tool like this one is the wrong place for real key material, because you can't verify what every browser extension or OS process around it might be doing.
How does the checksum work?
The generator takes raw entropy (128–256 bits, depending on word count), runs it through SHA-256, and appends the first few bits of that hash to the entropy before splitting everything into 11-bit chunks that map to wordlist indices. Because the checksum bits are a hash of the entropy itself, changing even one word breaks the checksum — which is exactly what the Validate tab checks for.
Why are there 12, 15, 18, 21, and 24-word options?
Each step adds 32 bits of entropy and roughly 3 words: 128 bits → 12 words, 160 → 15, 192 → 18, 224 → 21, and 256 → 24. Most consumer wallets default to 12 words (128-bit entropy, already far beyond brute-force range); 24 words is common for hardware wallets and protocols that want an extra security margin.
Does this use the real, official BIP-39 wordlist?
Yes — the exact 2,048-word English list and word order published in the bitcoin/bips repository. Word order matters because each word's position in the list is also its 11-bit code; a generator using a different word order would produce phrases that don't match what real wallet software expects.
Is anything sent to a server?
No. Entropy generation, SHA-256 hashing, and word lookup all run locally using your browser's Web Crypto API. Nothing about the phrase you generate or validate ever leaves your device.

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