Generate or check a BIP-39 mnemonic phrase locally in your browser - cryptographically random via Web Crypto, never uploaded.
Running locally on your device ...
No. Everything runs in your browser - your file never leaves your device. How this is verifiable
A BIP-39 mnemonic phrase (also called a seed phrase) is the plain-text representation of a cryptographic key that practically every modern cryptocurrency wallet (Bitcoin, Ethereum and most others) derives its addresses from. Instead of a hard-to-back-up binary key, you remember or write down 12, 15, 18, 21 or 24 words from a fixed 2048-word list (BIP-0039, the Bitcoin project official reference list). The last bits of every phrase are a built-in checksum that reliably catches a single typo when typing it back in later.
This tool generates a fresh, cryptographically random phrase at the length you want - only via the browser Web Crypto API randomness source (crypto.getRandomValues), never Math.random, because real money can depend on it. The other way round, you can enter an existing phrase: the tool checks the word count, whether every word is in the official list, and the built-in checksum - and honestly reports at which position a typo sits, instead of just saying "invalid".
Optionally you can also show the actual seed (a 64-byte hex value) that every wallet computes from the phrase via PBKDF2-HMAC-SHA512 (2048 rounds) plus an optional extra passphrase (the so-called 25th word) - this seed is the real input for deriving the wallet key (BIP-32).
The computation runs entirely locally in your browser; nothing is ever sent, stored or logged, and the tool keeps working offline after the first load. Still: never type a real wallet phrase that protects actual money into any web tool you do not fully trust - not even this one, even though its null-upload guarantee is technically provable. For a real wallet, use only a hardware wallet or the wallet own official software.
| Input formats | No file (generator) |
|---|---|
| Output format | TXT |
| Batch processing | No |
| Processing | Locally in your browser (JavaScript) |
| File upload | None |
Limitations: This tool supports only the official English BIP-39 word list - other BIP-39 languages (Japanese, Spanish, French and more) with their own normalization rules are deliberately not implemented. The check is a pure format and checksum check: it does not confirm that a wallet with a balance actually exists for a phrase. Important safety note: even though the computation is provably local, never take the risk - do not type a real wallet phrase that protects money into any web tool you do not fully trust.
No. Generation and checking run entirely locally in your browser via Web Crypto; nothing leaves your device, nothing is stored or logged.
We advise against a real, money-protecting phrase, no matter how trustworthy a web tool looks - use a hardware wallet or the official wallet software for that. This tool is suited for testing, learning and checking a phrase you already wrote down.
The phrase is the words themselves. The seed is a 64-byte value every wallet computes from the phrase (and optionally an extra passphrase) via PBKDF2-HMAC-SHA512 - it is the actual input for key derivation (BIP-32).
12, 15, 18, 21 or 24 words, corresponding to 128 to 256 bits of entropy - 12 words (128 bits) is the standard most wallets use.
The English list is the standard list virtually every wallet supports. Other BIP-39 languages have their own, sometimes different normalization rules (Japanese, for example, uses an ideographic space), which this tool deliberately does not replicate.
The check reports the exact word position where an unknown word sits, or that the built-in checksum does not match - so you find the error faster than by counting through it yourself.
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