Password Generator

How to generate a strong password

A password is strong when an attacker cannot guess it without trying an impractical number of attempts. That depends on one thing: how many possibilities there are, and how many of them an attacker gets to try per second. Length raises the first number faster than any other change you can make.

How long should a password be?

The US National Institute of Standards and Technology no longer asks for complicated rules. Its current guidance is a minimum of 15 characters for single-factor authentication, and it explicitly allows longer passphrases instead of symbol substitutions. Fifteen characters of lowercase alone hold more entropy than eight mixed characters with symbols.

That is why the slider here goes up to 64. There is no reason a password cannot be sixty-four characters long, and for accounts you rarely sign into, that is exactly what you should use.

What entropy means, and why length beats symbols

Entropy measures password strength in bits. Each bit doubles the work an attacker needs, so sixty bits is a million times harder than twenty. A lowercase character carries about 4.7 bits. A symbol carries about 5. Adding symbols to a long password barely moves the total; adding another four characters adds roughly nineteen bits.

This is also why the strength meter on this page shows bits instead of a made-up score out of one hundred. A bar that turns green is a promise nobody audited. A bit count can be checked.

Random password or memorable passphrase?

Both are valid, and the right choice depends on what you protect. Random strings are the strongest option and the hardest to remember, which is fine if you store them in a password manager. Passphrases trade a little strength for something you can recall without writing it down, and NIST considers four random words strong enough for most accounts.

The rule of thumb: use a random string for your email, banking and password manager, and use a passphrase for the forums you sign into once a year.

Why avoiding 0, O, 1, l and I matters

On a good screen with a clear font these characters are easy to tell apart. Copied by hand from a screen onto paper, or retyped from memory three months later, they are not. Turning on the option that removes them costs you very little strength and removes the most common reason a correct password gets rejected. The same reasoning applies to passwords read over the phone.

What this tool does not do

• Nothing is sent anywhere. Generation happens in your browser. The page works with the network off once it has loaded.
• Nothing is stored on disk. The history list lives only in the open tab and disappears when you close it. A saved password on your hard drive would outlive the tab and be readable by anyone using that browser profile.
• Randomness is cryptographic. It uses crypto.getRandomValues(), the same generator your browser uses for TLS keys. The Math.random() used by many online generators is not suitable: it is predictable from a handful of observed values.

After you generate one

One strong password is worth little if you reuse it. If a site you use is breached, the same password gives an attacker every other account where you used it, which is why credential stuffing is so effective. Turn on two-factor authentication wherever it is offered, and keep the recovery codes somewhere other than the device you lost.