BIP-39 Wordlist Inspector

A recovery phrase of twelve or twenty-four ordinary words is how many cryptocurrency wallets let people back up a key. The words come from a fixed list defined in BIP-39, and the way they encode a number is simple enough to understand in an afternoon. This page is an educational reference for that format: it looks up words and positions, and checks the structure of a test phrase. It is not a wallet, and it must never be used with a real phrase.

A warning first

Anyone who has your recovery phrase controls the funds it protects. No legitimate service, support agent or website needs it, and phishing sites work by asking for it. Treat typing a real phrase into a browser as a security failure, even on a page that says it stores nothing. Use only the sample phrase here, or made-up combinations of words, and learn the format from those. The page keeps what you type in the browser’s memory only and never saves or sends it, but safe habits are more reliable than promises.

The word list

The English list has 2048 words, so each word stands for 11 bits (2 to the power 11 is 2048). The words were chosen so that the first four letters identify a word uniquely, which is why wallets can accept shortened input, and so that similar-looking or similar-sounding words are avoided. The lookup box accepts the start of a word, a longer fragment of three letters or more, or a number from 1 to 2048. Results show the position in the list, the index counting from zero and the word’s 11 bits.

From words to bits and a checksum

A phrase is the entropy, random bits, followed by a few checksum bits, split into 11-bit groups. A 12-word phrase holds 132 bits: 128 of entropy and 4 of checksum. Fifteen words hold 160 and 5, eighteen hold 192 and 6, twenty-one hold 224 and 7, and twenty-four hold 256 and 8. The checksum is the first entropy-length divided by 32 bits of the SHA-256 hash of the entropy bytes. The last word therefore depends partly on the hash, which lets software detect most mistakes.

Using the page

In lookup mode, type a word fragment or number. In the check mode, press the Sample button or type a test phrase; the page lists any word not in the English list, warns if the number of words is not valid, and, if all is in order, reports whether the checksum matches. A table shows each word with its position and 11 bits, and a panel compares the checksum bits in the phrase with the expected bits.

A worked example

The sample is the first official test phrase: eleven times “abandon” followed by “about”. “abandon” is the first word, position 1 and index 0, so its 11 bits are all zero. “about” is position 4, index 3, which is 00000000011. The 128 bits of entropy are therefore zero, and the SHA-256 hash of sixteen zero bytes begins with the bits 0011, which are exactly the four checksum bits at the end of the phrase. The page reports that the checksum matches. It is a test vector and must never hold funds.

Limits

Only the English list is included, not the Chinese, Japanese, Spanish or other lists. A matching checksum shows that the phrase is well formed, not that any wallet uses it or that it is secure. The page does not turn phrases into seeds, keys or addresses, and it does not create new phrases, because doing that on a web page is unsafe. Use a hardware wallet or audited software for real keys.

Related tools

• Hash Generator computes the SHA-256 hash behind the checksum.
• Ethereum Address Checksum verifies another kind of error-detecting format.
• Base58 Encoder covers Base58Check checksums on Bitcoin addresses.
• Satoshi to BTC converts bitcoin amounts between units.