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.