BIP39 Mnemonic Phrase Generator

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Generate a 12 or 24-word BIP39 seed phrase, or check an existing phrase, locally in your browser. Words are chosen from the official 2048-word BIP39 English list using your browser's secure random number generator, with the checksum calculated as the standard requires. Paste a phrase to check its words and checksum, and see the entropy and seed it produces.

Anyone who sees a seed phrase can take the funds it protects. For a wallet that will hold real funds, generate the phrase on a hardware wallet or an offline computer. Never type an existing wallet's phrase into a website, including this one.

Number of words

Mnemonic phrase

Hide phrase

Entropy and seed (advanced)

Entropy (hex)

BIP39 passphrase (optional)

BIP39 seed (512-bit, hex)

The seed is what wallets derive keys from: PBKDF2-HMAC-SHA512 of the phrase, 2048 iterations, with "mnemonic" plus the passphrase as salt. A different passphrase gives a completely different wallet.

How to generate a seed phrase

Choose the number of words: 12 words (128-bit) or 24 words (256-bit) are the most common.
Select Generate phrase.
Write the words down in order, on paper or metal, and keep them somewhere safe and private.
Close the page when you are done. Nothing is saved.

Every phrase is new and random. Generating again gives a completely different phrase.

How to check a seed phrase

Type or paste a phrase into Mnemonic phrase. The tool checks, as you type, that:

every word is in the BIP39 English wordlist,
the phrase has 12, 15, 18, 21 or 24 words,
the checksum is correct: the last word partly depends on the others, which catches most typos and swapped words.

A valid checksum means the phrase is well formed, not that it belongs to a wallet with funds. To check a phrase you actually use, do it on a hardware wallet or an offline computer instead: see Security considerations.

How BIP39 phrases work

A phrase starts as random entropy. A checksum, the first bits of the entropy's SHA-256 hash, is added at the end, and the result is split into 11-bit groups. Each group is a number from 0 to 2047 that selects one word from the list.

Words	Entropy	Checksum	Total bits
12	128 bits	4 bits	132
15	160 bits	5 bits	165
18	192 bits	6 bits	198
21	224 bits	7 bits	231
24	256 bits	8 bits	264

Wallets then turn the phrase into a 512-bit seed with PBKDF2-HMAC-SHA512 (2048 iterations), and derive all keys and addresses from that seed with BIP32 and BIP44. Open Entropy and seed (advanced) to see the entropy and the seed for a phrase. The seed matches what BIP39-compatible wallets calculate.

The optional passphrase

BIP39 allows an optional passphrase, sometimes called the "25th word". It changes the seed completely, so the same phrase with a different passphrase opens a different wallet. A passphrase adds protection if the phrase is found, but if you forget it, the wallet cannot be recovered.

12 or 24 words?

Both are secure. 12 words give 128 bits of entropy, which is far beyond what can be guessed by brute force. 24 words give 256 bits and are the default on many hardware wallets. Choose the length your wallet expects; most wallets accept both.

Security considerations

The phrase is generated on your device. The tool uses the Web Crypto API's secure random number generator. The phrase is never sent to a server or saved, and reloading the page discards it.
A seed phrase is the wallet. Anyone who sees it can take the funds, and lost phrases cannot be recovered. Never share it, photograph it or store it in cloud notes.
For real funds, prefer a hardware wallet. Hardware wallets generate the phrase inside the device, where no website, browser extension or malware can see it.
If you use this page, reduce the risk. Load the page, disconnect from the internet, generate and write down the phrase, then close the browser tab before reconnecting. Use a computer you trust, without unknown browser extensions. This page does not show ads, but like the rest of the site it loads analytics scripts.
Never enter an existing wallet's phrase into a website. Phishing sites often ask for seed phrases. Legitimate wallets and support staff never need yours.

Frequently asked questions

Is the seed phrase sent to a server?

No. The phrase is generated and checked in your browser, and is never uploaded or saved. For real funds, still prefer a hardware wallet or an offline computer, because any software running on your device can see what is on the screen.

Is a randomly generated phrase secure?

Yes, if the randomness is secure. This tool uses the browser's cryptographically secure random number generator, the same source used for encryption keys. A 12-word phrase has 2¹²⁸ possible values, far too many to guess.

Can I make up my own seed phrase?

No. People are bad at choosing random words, and a phrase with a valid checksum is hard to create by hand. Phrases chosen by people, such as song lyrics or quotes, have been guessed and emptied.

Why does my phrase show "The checksum does not match"?

The last word partly depends on all the others. If one word is wrong, missing or in the wrong place, the checksum usually fails. Check each word against your written copy.

Which wallets use BIP39 phrases?

Most cryptocurrency wallets, including Ledger, Trezor, MetaMask and Electrum (with the BIP39 option), use BIP39 phrases for Bitcoin, Ethereum and many other blockchains. The same phrase can restore the wallet in any compatible app.

Keccak-256 hash calculator — Calculate Ethereum's Keccak-256 hashes.
SHA-256 hash calculator — Calculate SHA-256, the hash behind the BIP39 checksum.
Password generator — Create a strong BIP39 passphrase.
AES encryption and decryption — Encrypt text and files with a password.