--- title: "BIP39 Seed Phrase Generator: Free Online Tool, 12–24 Words" url: "https://bip39-phrase.com/generator-seed-phrase/" language: "en" updated: "2026-10-19T00:00:00+00:00" --- # BIP39 Mnemonic Seed Phrase Generator Generate a random BIP39 mnemonic of 12, 15, 18, 21 or 24 words in any of the 10 official wordlist languages. The words come from your browser's cryptographically secure random number generator, with the BIP39 checksum in the last word. Updated October 19, 2026 Эта страница по-русски: [Генератор сид-фразы BIP39](/ru/generator-sid-frazy/) ## How the BIP39 generator creates a seed phrase New to seed phrases? Start with [what a seed phrase is and how a wallet restores from it](/recovery-seed-phrase-guide/). Each time you press Generate Mnemonic, the tool follows the [BIP39 specification](https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki), using the `@scure/bip39` library: 1. **Entropy.** It takes fresh random bits from your browser's `crypto.getRandomValues()`: 128 bits for 12 words, up to 256 for 24\. This number is the actual secret; the Entropy (hex) field shows it. 2. **Checksum.** It hashes the entropy with SHA-256 and appends the first ENT/32 bits of the hash, where ENT is the entropy length: 4 bits for 128-bit entropy, 8 for 256. 3. **Word indexes.** It cuts the combined bits into groups of 11\. Each group is a number from 0 to 2047, the position of a word in the 2048-word list. 4. **Words.** It looks each number up in the wordlist of the language you picked. The [BIP39 visualizer](/how-bip39-works/) runs these four steps on any test entropy and shows every bit: the SHA-256 checksum, the 11-bit groups and the word each one picks. Because the checksum comes last, the final word is only partly random. In a 12-word phrase it holds 7 random bits and 4 checksum bits, so after any 11 words only 128 of the 2048 words complete a valid phrase; in a 24-word phrase, 3 random bits and 8 checksum bits leave 8 valid last words. The checksum lets wallets reject most typos; the [BIP39 checksum checker](/bip39-checksum-checker/) runs the same test on a test phrase, and the [last word calculator](/bip39-last-word-calculator/) lists the valid final words. Hand-picked words usually fail it, and people choose far less randomly than a computer, which is [why you should never make up your own seed phrase](/why-you-should-never-create-your-own-seed-phrase/). ## 12 or 24 words: what the length changes Each extra 32 bits of entropy adds one checksum bit and three words, as in the BIP39 table. Since the checksum is fixed by the entropy, the number of possible phrases equals the number of entropy values. | Words | Entropy | Checksum | Total bits | Entropy in hex | Possible phrases | | ----- | -------- | -------- | ---------- | -------------- | ---------------- | | 12 | 128 bits | 4 bits | 132 | 32 characters | 2128 | | 15 | 160 bits | 5 bits | 165 | 40 characters | 2160 | | 18 | 192 bits | 6 bits | 198 | 48 characters | 2192 | | 21 | 224 bits | 7 bits | 231 | 56 characters | 2224 | | 24 | 256 bits | 8 bits | 264 | 64 characters | 2256 | Twelve words already put brute force out of reach: 2128 is about 3.4 × 1038 phrases, and 128 bits matches the security level of secp256k1, the elliptic curve behind Bitcoin and Ethereum keys. Twenty-four words add margin for long-term cold storage, as our [security notes](/security/) suggest. Wallets most often create 12 or 24 words; support for 15, 18 and 21 varies, so check yours before using those lengths. ## Which wordlist language to use The generator offers all ten official BIP39 wordlists: English, Japanese, Korean, Spanish, Chinese (Simplified and Traditional), French, Italian, Czech and Portuguese. For a real wallet, choose English: BIP39 itself notes that the vast majority of wallets support only the English list and strongly discourages generating phrases in other languages. The language cannot be changed later, because the seed is computed from the words rather than from the entropy: the same entropy written in Spanish and in English opens two different wallets. In [the complete BIP39 English wordlist](/) the first four letters of every word are unique, which helps when you check a backup. ## Where the phrase is generated The generator runs locally in your browser tab, so once the page has loaded it keeps working offline. That makes it useful for learning, testing wallet software and checking implementations. Our guide on [how to create a seed phrase in a wallet](/create-a-seed-phrase/) walks through choosing a wallet and confirming the words. ## After you generate a phrase Wherever the words come from, the next steps are the same: 1. **Write it down by hand**, numbered and in order, and check every word against the wordlist. Never photograph it or keep it in a file, email or cloud note. 2. **Store the copy safely**, on paper or metal and away from the device; see [how to store a seed phrase safely](/store-a-seed-phrase/). 3. **Test a restore** before you deposit anything: restore the wallet from your written copy, on a reset device or in a second wallet app, and confirm it shows the same first receiving address. ## Check an implementation with the BIP39 test vector BIP39 links to official test vectors in [python-mnemonic](https://github.com/trezor/python-mnemonic/blob/master/vectors.json), its reference implementation; every BIP39 library should reproduce them. The first vector starts from 128 zero bits: Entropy (hex) 00000000000000000000000000000000 Mnemonic abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about Seed with the passphrase TREZOR c55257c360c07c72029aebc1b53c05ed0362ada38ead3e3e9efa3708e53495531f09a6987599d18264c1e1c92f2cf141630c7a3c4ab7c81b2f001698e7463b04 BIP32 root key xprv9s21ZrQH143K3h3fDYiay8mocZ3afhfULfb5GX8kCBdno77K4HiA15Tg23wpbeF1pLfs1c5SPmYHrEpTuuRhxMwvKDwqdKiGJS9XFKzUsAF Why it ends in _about_: the first 121 bits are zero, so the first 11 indexes are 0 (_abandon_). The last group holds the remaining 7 zero bits plus the 4-bit checksum; SHA-256 of 16 zero bytes begins with 0x37 (binary 0011 0111), so the checksum is 0011 and the last index is 3: _about_. This generator cannot take entropy as input. To see the vector reproduced on this site, open the entropy panel of the [mnemonic code converter](/seed-phrase-to-private-key-converter/), turn the entropy into the phrase (or paste the phrase), enter the passphrase TREZOR and compare the seed and root key. The 24-word vector works the same way: 256 zero bits give 23 times _abandon_ followed by _art_, and with TREZOR the seed begins `bda85446c684`. ## BIP39 Generator — Frequently Asked Questions Does the generator work offline? Yes, once the page has fully loaded and the Generate Mnemonic button works. You can then disconnect, generate a phrase, write it down and close the tab before reconnecting. Should I generate 12 or 24 words? Both are secure with good randomness. Twelve words carry 128 bits of entropy, which matches the 128-bit security level of secp256k1, the curve behind Bitcoin and Ethereum keys; 24 words carry 256 bits for extra margin in long-term storage. Check that your wallet restores 15, 18 or 21 words before using those lengths. Can I pick 12 words from the wordlist myself? It is not recommended. People choose far less randomly than a computer, so hand-picked phrases are easier to guess, and a random set of 12 words passes the checksum only once in 16 tries (once in 256 for 24 words). BIP39 is meant to encode computer-generated randomness, not sentences people make up. Can two people generate the same seed phrase? Not in practice. There are 2¹²⁸ (about 3.4 × 10³⁸) possible 12-word phrases and 2²⁵⁶ possible 24-word phrases, so with a working cryptographic random number generator a repeat is negligibly unlikely. The practical risks are weak randomness and exposed backups. Which language should I choose? English, unless you know your wallet supports another list: BIP39 notes that the vast majority of wallets support only English and strongly discourages generating phrases from the other lists. A phrase cannot be translated later, because the seed is derived from the words; the same entropy in another language opens a different wallet. Can I add a passphrase to the generated phrase? Not in this generator, which creates only the words. A BIP39 passphrase is applied when the words are turned into a seed, so you set it in your wallet. Every passphrase opens a valid but different wallet, so without the exact passphrase the words alone will not restore the funds. What does the Entropy (hex) field show? The random number the words encode, in hexadecimal: 32 characters (128 bits) for 12 words, up to 64 (256 bits) for 24\. The phrase and the entropy convert into each other with the wordlist, so the entropy is as secret as the phrase. ## Offline version The generator, checksum checker, last word calculator and seed phrase converter in a single HTML file: it opens in a browser with no internet connection and makes no network requests. [Download the offline version (HTML, 522 KB)](/downloads/bip39-tools-offline.html) Check the file’s SHA-256 before you open it: `96396acd75801a3a271b716cd0666bf006c613e8e6f7be5e47de7330bcec2887` macOS and Linux: shasum -a 256 bip39-tools-offline.html; Windows: certutil -hashfile bip39-tools-offline.html SHA256\. v1.0.0, 2026-10-19. ## Guides - [How to Create a Seed Phrase: Step-by-Step Guide and Examples](/create-a-seed-phrase/) To create a seed phrase, set up a new wallet and let it generate 12 to 24 BIP39 words, then write them down in order, confirm them and test the backup. - [How to Store a Seed Phrase: Paper, Steel and Safe Locations](/store-a-seed-phrase/) Store a seed phrase offline on paper or stamped steel, in at least two separate places, never as a photo or file, and test each copy by restoring from it. - [BIP39 Wallets: Which Wallets Support BIP39 Seed Phrases (Compared)](/bip39-wallets/) Which wallets support BIP39 seed phrases: 37 hardware, desktop, mobile and browser wallets compared by phrase length, passphrase, SLIP-39 and derivation path. - [How to Generate a BIP39 Seed Phrase with Dice, Step by Step](/seed-phrase-with-dice/) Each roll of a fair die adds 2.585 bits: 50 rolls make a 12-word BIP39 seed phrase, 99 a 24-word one. Two methods, a worked example and the last word. - [Why You Should Never Create Your Own Seed Phrase](/why-you-should-never-create-your-own-seed-phrase/) Words you pick are far easier to guess than random ones; brain wallets made from invented phrases were usually drained within a day. Use a generator or dice. - [Can You Guess a Seed Phrase? Probability and Real Risks](/can-you-guess-a-seed-phrase-probability-and-real-risks/) No: a random 12-word BIP39 phrase is one of 2¹²⁸ possibilities and a 24-word one of 2²⁵⁶; real losses come from weak generators, self-chosen words and scams.