Password Generator

A password is only as strong as the number of guesses needed to find it, and that number depends on two things: how many characters it has, and how many possibilities each character could have been. Everything else — the symbol you bolted onto the end, the digit swapped for a letter — barely moves it.

This generator builds passwords from your browser's cryptographic random source and shows the entropy in bits alongside an estimated time to exhaust it. It also generates passphrases, which are far easier to remember and, at four or five words, considerably stronger than the passwords most people type from memory.

Each bit of entropy doubles the number of guesses an attacker needs. A 40-bit password takes roughly a trillion guesses to exhaust; a 60-bit one takes about a million times more than that.

This is why length beats complexity. Adding one character to a mixed-case alphanumeric password adds about six bits. Adding one symbol type to a short password adds one or two. A twenty-character lowercase-only password is stronger than an eight-character one using every symbol on the keyboard.

The figure assumes ten billion guesses a second, which is a reasonable order of magnitude for an attacker with commodity GPUs working offline against a stolen password database.

It is an order of magnitude, not a promise. The real number depends entirely on how the site stored your password: a modern algorithm like argon2 or bcrypt slows an attacker down by orders of magnitude, while an unsalted SHA-1 hash speeds them up by them. You have no way to know which one a site used, which is the argument for a password long enough that it does not matter.

For the two or three passwords you actually have to remember — the one on your password manager, your device login — a passphrase of four or five random words is easier to hold in your head and stronger than the substituted-character password most people would invent instead.

The strength comes from the number of words, not from the word list being secret. This is the Diceware principle: the list here is public, and a four-word phrase drawn from it is still drawn from billions of possibilities. What breaks it is choosing the words yourself, because people do not choose randomly.

The randomness comes from crypto.getRandomValues, the browser's cryptographically secure generator, which is the same primitive password managers use. It is not Math.random, which is fast, predictable and unsuitable for anything security-related.

Nothing is transmitted. The page does no network request while generating, keeps no history, and stores nothing — close the tab and the password is gone unless you saved it. That is the intended behaviour, so save it somewhere before you navigate away.