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BIP39 Mnemonic Converter

DeveloperSecurity

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INPUT

OUTPUT

Client Side

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Guide

BIP39 Mnemonic Converter

Generate new BIP39 mnemonic seed phrases or convert an existing phrase to its corresponding seed, extended private key (xprv), and derivation path. Supports 12, 15, 18, 21, and 24-word phrases with an optional passphrase (BIP39 passphrase / 25th word). All computation is fully client-side.

How to Use

Choose Generate to create a new random mnemonic, or Convert to derive keys from an existing phrase. Select your word count (12 to 24), optionally enter a passphrase, then view the derived seed hex and extended private key. Use the built-in example to test with a known mnemonic.

Features

Generate or convert – create new mnemonics or derive from existing ones
5 word counts – 12, 15, 18, 21, or 24 words
Optional passphrase – BIP39 25th word / passphrase support
Seed and xprv output – 512-bit seed hex and BIP32 extended private key
BIP39 standard – 2048-word English wordlist, PBKDF2-HMAC-SHA512 derivation
Client-side only – seed phrases never leave your browser

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 FAQ

What is BIP39 and how does it work?

BIP39 (Bitcoin Improvement Proposal 39) standardises the generation of deterministic wallets from a human-readable mnemonic phrase. A random entropy value (128–256 bits) is hashed with SHA-256, a checksum is appended, and the result is split into 11-bit groups that index into a 2048-word wordlist. The mnemonic is then converted to a 512-bit seed via PBKDF2-HMAC-SHA512 with 2048 iterations, which seeds a BIP32 hierarchical deterministic wallet.
What is the BIP39 passphrase (25th word)?

The BIP39 passphrase is an optional additional input to the PBKDF2 seed derivation function. It is sometimes called the 25th word but is not from the BIP39 wordlist — it can be any string. Using a passphrase creates a completely different wallet from the same mnemonic, providing plausible deniability: you can have a decoy wallet with small funds at the mnemonic alone and a main wallet at mnemonic + passphrase.
How does mnemonic word count affect security?

12 words = 128 bits of entropy, 15 words = 160 bits, 18 words = 192 bits, 21 words = 224 bits, 24 words = 256 bits. With 128 bits, the search space is 2¹²⁸ possible mnemonics — computationally infeasible to brute-force with any foreseeable technology. The extra bits in 24-word phrases provide a larger margin against future cryptanalytic advances but are not practically necessary for current security.
Why should BIP39 mnemonics never be entered on online tools for real wallets?

A real wallet mnemonic is the master key to all funds. Any tool, website, browser extension, or clipboard that sees your mnemonic could exfiltrate it. For practice and learning, test with example or randomly generated phrases. For real wallets, generate and store the mnemonic on air-gapped hardware (hardware wallets like Ledger or Trezor) and never type it into any internet-connected device.