What this tool does
Paste 12 or 24 words (one per line, or separated by spaces). The page checks four things, all locally in your browser:
- Wordlist membership. Each word must appear in the official BIP-39 English wordlist (2048 entries). One typo and the seed is invalid.
- Checksum validity. BIP-39 encodes a 4-bit (12-word) or 8-bit (24-word) checksum in the last word. The check fails if any word in the phrase is wrong, even one — so a valid checksum is strong evidence the entire phrase is correct.
- Hexadecimal entropy. The numerical entropy the seed encodes, in hex. Useful for cross-referencing against a hardware-wallet's displayed entropy on first setup.
- Word position numbers. The index of each word in the BIP-39 list. Useful for cold-storage backups where you want to write numbers instead of words (numbers are harder to misread than handwritten English).
What this tool does not do
It does not generate seeds. It does not derive addresses. It does not connect to any blockchain. There is no input field that accepts your private key. The only data that enters the page is the 12 or 24 words you paste; the only data that leaves the page is the data you see on screen.
The privacy model
JavaScript runs entirely in your browser. No network requests, no analytics, no error reporting. You can verify this by opening the browser's developer tools (F12), going to the Network tab, and pasting a seed — you should see zero network activity. If you want to be extra cautious, save this HTML file (right click → Save As) and run it on an air-gapped device with no network connection. Everything still works.
When to use this
- You just transcribed a seed from a hardware device to paper, and want to verify the paper version before storing it. Type the paper version in, confirm checksum.
- You are evaluating a piece of paper or metal plate found in storage, and want to know if the seed on it is still cryptographically valid (i.e. the words haven't degraded into illegibility that produces a checksum failure).
- You are about to set up a hardware wallet and want to understand the BIP-39 system before generating the seed for real. Try this tool with a known test seed (the BIP-39 spec includes test vectors) and verify it returns the documented checksum.
What the tool will not catch
It cannot tell you whether a valid seed is YOUR seed, or someone else's. A pre-initialized hardware wallet from a third-party seller will display a perfectly valid checksum-passing seed — that seed is just also known to the seller. This tool checks format, not provenance.
This tool runs the full BIP-39 check — wordlist membership (2048 words) and SHA-256 checksum — entirely in your browser. A passing checksum is strong evidence the whole phrase is correct, but it cannot tell you whether the seed is yours: anyone can generate a valid mnemonic.
Never paste a real seed phrase into any online device. Even though this page sends nothing, offline is still safest. To check a real wallet seed and view derived addresses, use iancoleman/bip39 offline HTML version: download standalone.html, go offline, open it in a private window.
Paste or type your (test) mnemonic
Space-separated lowercase English words. This tool never saves, uploads, or logs. Closing the page destroys it.
Waiting for input...
Paste a mnemonic above, click "Check" to see results.
What this tool can check · and what it can't
Can check
- Valid word count: BIP-39 standard is 12 / 15 / 18 / 21 / 24 words. Anything else is wrong.
- Wordlist membership: every word is checked against the fixed 2048-word BIP-39 English list; "loremipsum" looks fine but is flagged because it isn't on the list.
- Checksum (SHA-256): the checksum is recomputed per the BIP-39 spec. One wrong word, or a scrambled order, breaks it — so a passing checksum is strong evidence the whole phrase is correct.
- Entropy & word positions: once the phrase passes, you get the hex entropy it encodes plus each word's index in the list (useful for number-based cold backups).
- Case issues: BIP-39 is all lowercase. Uppercase is flagged (but lowercased automatically before checking).
Can't check
- Whether the seed is yours: anyone can generate a valid mnemonic. A pre-initialized hardware wallet from a third-party seller shows a checksum-passing seed the seller also knows. This checks format and cryptographic validity, not provenance.
- Derived addresses or balances: those require chain queries or BIP-32 derivation; this tool deliberately makes zero network requests and derives no addresses.
- The optional passphrase (25th word): a BIP-39 passphrase doesn't affect the mnemonic's own checksum, so it isn't handled here.
To view derived addresses, use this
- Visit
github.com/iancoleman/bip39 - Download
bip39-standalone.html(single file / offline HTML / full wordlist included) - Disconnect ethernet / turn off WiFi / open the downloaded HTML in private mode
- Run the check on your seed / view derived addresses
- Close the browser (private mode wipes everything automatically)
This process is not paranoia. Any online seed-generating or seed-checking tool carries risk of keylogging, malicious browser extensions, or injected scripts. Offline when you can.