CalcOak

Password Generator: random passwords and passphrases with an honest strength estimate

StrengthVery strong
Entropy
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Time to crack at 10 billion guesses/s
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Generated entirely in your browser with the Web Crypto API. Nothing is sent to a server and nothing is stored.

How to use this generator

The random password tab produces a fresh 16-character password the moment the page loads, and every option you change generates a new one immediately. Drag the slider or type an exact length between 8 and 64, untick any character class a site refuses to accept, and switch on "exclude ambiguous characters" if you will ever have to read the password off a screen or type it into a TV. "No repeated characters" exists for the few systems that demand it. Press Copy, or tick "Generate 5" to see five candidates and copy the one you like.

The passphrase tab strings together words from a built-in list of 1,000 short English words. Pick three to eight words and a separator, and optionally capitalise each word or add a two-digit number for sites that insist on an uppercase letter or a digit. A phrase such as "Copper-Marble-Silent-Wheel" is far easier to memorise or read out over the phone than a string of symbols, and at about 40 bits it is still beyond anything a person could guess by hand.

Why entropy matters more than complexity rules

"Must contain a capital, a number and a symbol" policies were written for people who would otherwise choose "sunshine". They do little against a cracking rig, because people satisfy them predictably: "Sunshine1!" is in every dictionary attack. What actually resists guessing is entropy, the number of equally likely possibilities the attacker has to work through. Eight random characters from a 94-symbol pool is 52 bits; a modern GPU cluster running at 10 billion guesses a second clears that in a few days. Sixteen characters is 105 bits, which is tens of trillions of years at the same rate. Length beats cleverness, which is why a six-word passphrase, at roughly 60 bits, outperforms a short "complex" password while remaining something you can say aloud.

The quality of the randomness matters too. Generators built on Math.random produce sequences that can be predicted from a few outputs; this page uses crypto.getRandomValues, the operating-system entropy source browsers use for TLS keys, and rejects out-of-range samples so every character is equally likely. The best habit is to let a password manager remember unique random passwords for every account and reserve a long passphrase for the two things you must type from memory: the manager itself and your computer login. Generate either here, then close the tab.

Further reading

Frequently asked questions

How is the entropy figure calculated?+

Entropy measures how many equally likely outcomes the generator could have produced, expressed in bits. For a random password it is log2 of the character pool size multiplied by the length: 16 characters drawn from all 94 printable ASCII characters gives about 104.9 bits. For a passphrase it is log2 of the word list size multiplied by the number of words. This tool uses a 1,000-word list, so each word contributes just under 10 bits, and an appended two-digit number adds another 6.6 bits.

Are these passwords really random?+

Yes. Every character and word is chosen with the browser's Web Crypto API (crypto.getRandomValues), which draws from the operating system's cryptographic random source rather than the predictable Math.random function. The tool also uses rejection sampling when mapping random 32-bit values onto the pool, so no character is ever slightly more likely than another because of a modulo bias.

Is a four-word passphrase strong enough?+

Four words from a 1,000-word list is about 40 bits, which is fine for accounts that lock out after a few wrong attempts but too weak for anything that could be attacked offline, such as a stolen password database, a disk-encryption key or a password manager vault. For those, use six or more words, or switch to a 16-character random password of 100+ bits.

Does the "time to crack" figure mean my account is safe for that long?+

It is an estimate of how long an attacker with 10 billion guesses per second would take, on average, to find the password by trying every possibility; that is roughly what a single machine with several modern graphics cards achieves against a fast hash. Real attacks are usually slower if the site hashes passwords properly, or irrelevant if the password is leaked in plain text, phished or reused on another site. Treat it as a comparison between options rather than a guarantee.

Is anything I generate here sent or saved anywhere?+

No. The page has no server component: generation, entropy maths and clipboard copying all happen inside your browser tab, nothing is written to local storage, and the passwords disappear as soon as you leave or refresh the page. You can load the page, disconnect from the internet and it will still work.

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