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BIP39 Mnemonic Generator — Seed Phrase Creator

Free online BIP39 mnemonic generator. Create 12-24 word seed phrases with cryptographic entropy and checksum validation. No sign-up, runs in your browser.

Free to use No sign-up Runs in your browser

Tool workspace

A recovery phrase controls real funds. Generate wallet seeds on an offline, trusted device — never from a phrase shown in a shared or online browser session.

Use my own entropy (advanced)

Leave empty to use the browser secure random generator. Supply 32, 40, 48, 56, or 64 hex characters to reproduce a known test vector.

Check an existing phrase

The full 2048-word BIP-39 English list ships with this page. Generation, checksum verification, and validation run entirely in your browser with no network request.

What Is a BIP39 Mnemonic?

BIP39 (Bitcoin Improvement Proposal 39) defines a standard for generating mnemonic phrases from random entropy. These human-readable word sequences (typically 12 or 24 words) encode the master seed for hierarchical deterministic (HD) wallets used in Bitcoin, Ethereum, and many other cryptocurrencies. The mnemonic includes a checksum to detect transcription errors. This page embeds the complete 2048-word BIP39 English wordlist, so every word index, checksum, and validation result is computed offline against the specification rather than a downloaded list.

How to Use This BIP39 Generator

  1. 1Select the number of words (12, 15, 18, 21, or 24).
  2. 2Click Generate Mnemonic to create a cryptographically secure seed phrase.
  3. 3Copy the phrase and store it securely offline. Never share your real wallet seed phrase online.
  4. 4Optionally open the advanced entropy panel and paste known hex entropy to reproduce an official BIP39 test vector.
  5. 5Use the Check Phrase section to see word count, unknown words, repeated words, and whether the BIP39 checksum matches.

Common Use Cases

Wallet Development Testing

Generate test mnemonics for developing and testing cryptocurrency wallet software.

Checksum Validation

Verify that a mnemonic phrase is valid BIP39 with correct checksum before importing into a wallet.

Learning Cryptography

Understand how entropy, checksums, and mnemonic encoding work in the BIP39 standard.

Frequently asked questions

Should I use this for my real cryptocurrency wallet?

This tool is designed for testing and educational purposes. For real wallets, use a hardware wallet or trusted wallet software that generates mnemonics offline on a trusted device.

How is the entropy generated?

The tool uses the Web Crypto API crypto.getRandomValues() for cryptographically secure random number generation, the same source used by browsers for TLS and other security operations.

What is the checksum in BIP39?

BIP39 appends a SHA-256 checksum to the entropy bits before splitting into 11-bit word indices. For a 12-word mnemonic (128 bits entropy), 4 checksum bits are appended. This catches transcription errors.

Does this page download the wordlist?

No. The complete 2048-word BIP39 English wordlist is bundled with the page. A seed tool must never depend on a runtime download, because a blocked or altered response could otherwise produce a phrase that no wallet can restore. You can verify the tool offline: disconnect from the network, enter entropy of 32 zeroes, and confirm it returns the official vector ending in "about".