Password & Key Generator

Where the randomness comes from

Every value on this page is built from crypto.getRandomValues(), the browser's cryptographically secure random number generator, seeded by the operating system. It is the same source password managers and TLS use. Math.random() is never involved: it is fast and fine for games, but its output can be predicted and it must never be used for secrets.

Nothing you generate leaves your device. There is no server call, no logging and no analytics on the values, and the page only saves your settings (length, character sets) in the address bar so you can bookmark a configuration. The values themselves are never put in the URL.

Avoiding modulo bias

The naive way to pick a random character is bytes[i] % alphabet.length. With a 62 character alphabet and a random byte (0 to 255), the first 8 characters come up slightly more often, because 256 is not a multiple of 62. This tool uses rejection sampling instead: it draws a 32-bit number, throws it away if it falls in the uneven tail, and only then takes the remainder. Every character is exactly equally likely.

function randInt(n) {
  const limit = Math.floor(2 ** 32 / n) * n;
  const buf = new Uint32Array(1);
  do crypto.getRandomValues(buf); while (buf[0] >= limit);
  return buf[0] % n;
}

Reading the entropy number

Entropy is length × log2(alphabet size) for random strings, and words × log2(list size) for passphrases. It assumes the attacker knows exactly how the value was made, which is the honest way to measure. Rough guidance:

• Under 50 bits: weak for anything that can be attacked offline.
• 60 to 80 bits: a strong user password, provided the site stores it with bcrypt, scrypt or Argon2.
• 128 bits and up: API keys, session tokens, password reset links and anything a machine checks millions of times per second.
• 256 bits: HMAC signing secrets for JWTs (HS256) and encryption keys.

Picking the right mode

Password is for accounts that live in a password manager. Go long (20 or more) and let the manager remember it. Passphrase is for the few secrets you must type or remember, like the manager's master password or a disk encryption key. API key mimics the prefixed format popularized by Stripe, which makes keys greppable and lets secret scanners on GitHub catch leaks. UUID v4 gives 122 random bits, ideal for public identifiers, but do not treat a UUID as a secret token by itself unless your threat model is relaxed. Secret bytes matches what you would get from openssl rand -hex 32 or openssl rand -base64 32.

# .env
JWT_SECRET=6f1c...e9a2   # 32 bytes, hex encoded
SESSION_SECRET=Q2x...    # 32 bytes, base64

Frequently asked questions