PassCheck

Passphrases you can actually type

Random words from a 1,392-word list — 10.44 bits each, chosen by the machine rather than by you.

Network measuring… Source crypto.getRandomValues

Check it yourself: open DevTools → Network and use this page. Nothing you generate or type produces a request, because the page makes none.

The maths, stated plainly

This list contains 1,392 words. Choosing one at random contributes log₂(1,392) = 10.44 bits of entropy. The words are independent, so n words give 10.44 × n bits:

WordsEntropyPossible phrasesSuitable for
441.8 bits3.8 × 10¹²Not enough on its own
552.2 bits5.2 × 10¹⁵Low-value accounts
662.7 bits7.3 × 10¹⁸Ordinary accounts
773.1 bits1.0 × 10²²Password manager master, email
883.5 bits1.4 × 10²⁵Disk encryption, key material

Note what is not in that calculation: any assumption that the attacker is unaware of the list, the separator, or the word count. Entropy is counted assuming they know all of it. That is why the honest figure is lower than the ones some sites advertise, and why it can be relied on.

Why a phrase you made up yourself does not count

The entropy above depends entirely on the words being drawn uniformly at random. A passphrase you compose is not: people pick concrete nouns, follow grammatical order, choose thematically related words, and favour the same few thousand familiar terms. Attack tools model exactly those tendencies. A self-invented four-word phrase can have less real entropy than a well-chosen single word, which is precisely why the machine draws them here.

When to add the digits

Only when a site's validation forces you to. Appending two digits adds 6.6 bits, which is a fraction of one extra word — so if you have the choice, add a word instead. The option exists because a great many login forms still reject a perfectly strong passphrase for containing no number.

Also here

Password generatorRandom characters when a passphrase will not fitStrength checkerSee what a cracker sees in a password you already use

Questions

How much entropy does each word add?
Exactly log₂ of the wordlist size. This list holds 1,392 words, so each one contributes 10.44 bits — six words is 62.7 bits, seven is 73.1. That figure only holds if the words are chosen uniformly at random by the machine, which they are. A passphrase you invented yourself has dramatically less entropy than the same number of words drawn randomly, because human choices cluster hard.
Is a passphrase weaker than a random password?
Per character, much weaker. Per unit of human effort, considerably stronger. Six random words here is about 63 bits in 30-odd very typable characters; matching that with random characters takes about 11 characters that you will get wrong when you type them. The reason passphrases win in practice is that people actually use them correctly rather than writing them on a sticky note.
Does the attacker knowing the wordlist matter?
No, and this is the most common misunderstanding about passphrases. The entropy calculation already assumes the attacker knows the list and the number of words and the separator — it is the count of possible combinations given all of that. Secrecy of the method contributes nothing and is never counted. A list of 1,392 words with six drawn at random gives 1,392⁶ possibilities, which is about 7×10¹⁸.
How many words should I use?
Six for ordinary accounts, seven or more for anything that guards other credentials — a password manager's master password, a disk encryption key, an email account that can reset everything else. The jump from six to seven costs you one word to type and multiplies the attacker's work by 1,392.
Why these words?
They are common English words of four to six letters, filtered to be unambiguous when spoken aloud and quick to type. Short words keep the phrase manageable; familiar words make it memorable; and avoiding near-homophones means you can read it to somebody over the phone without spelling every letter.