A random password or a passphrase from English words. Generated in your browser from a cryptographically secure source of randomness; passwords never leave it.
The tool builds a password in two shapes. A random run of characters suits accounts whose password you never have to remember, because a password manager holds it. A passphrase — several randomly drawn words in a row — suits the places where you have to know the password by heart and occasionally type it on somebody else's keyboard. For both shapes the entropy in bits is shown, that is, how much randomness the password actually contains.
Passwords are created in your browser and are not sent anywhere. They are not written to browser storage, to the page address or to any cookie, so they never reach your browsing history either; when you close the page they simply disappear. What the page itself loads and measures is covered in the section on how the generation works. On a shared or borrowed computer, though, it is better not to generate passwords at all — a malicious browser extension can read the contents of the page just as it can on any other.
What the tool is for and what it is not
The generator produces random strings and computes entropy from how they were produced. It does not assess a password you thought up yourself, and it says nothing about the service where you will use it. Entropy describes the strength of the method, not the quality of one particular result: even a password with a hundred bits of randomness is worthless if it works in two places, sits in a notepad file, or gets typed into a spoofed login page.
Password shape
Extra length adds more bits than a wider alphabet does. If you do not have to remember the password, there is no reason to go below twenty characters.
What to draw from
The set is limited to characters that pass through login forms and the command line without trouble. These are what it draws from: !@#$%^&*()-_=+[]{};:,.?/
Useful when you will be copying the password off paper or reading it out loud. It shrinks the alphabet, and with it the entropy per character — the tool accounts for that in the calculation. These are left out: 0 O o 1 l I 5 S 2 Z
Every word adds the same number of bits. You control the strength of a passphrase by the number of words; nothing else has any effect on it.
Cosmetic, for forms that insist on a capital letter. It is fixed, and therefore adds not a single bit of entropy.
The digit is drawn the same way as the rest, so it really does raise entropy by log2(10). Its main purpose is to satisfy rules of the "the password must contain a digit" kind.
Entropy—bits
Rating in words: —
The rating in words is only a translation of the number into words, along boundaries we chose ourselves. It is not a standard and not a certification. What decides is the number itself and what the password has to protect.
How to read the result
What entropy means
Entropy in bits says how many options an attacker would have to work through if they knew absolutely everything about the method except the result itself. Every bit added doubles the number of options: a password with sixty bits has a million times more of them than a password with forty.
The number describes the method, not the particular string. The password aaaaaaaa drawn from an alphabet of 86 characters has exactly the same entropy as any other eight-character result — it is just thoroughly improbable. For the same reason, the entropy of a password you thought up yourself cannot be computed: nobody knows how many options you were choosing from.
You will deliberately not find a time to crack here. It depends on who is attacking, on whether they are guessing through a login form or offline from a stolen database, and on how the password is stored in it. Between a service with a modern password-storage function and one that kept passwords as a bare hash, the difference is orders of magnitude. A figure in years would therefore be invented.
Entropy does not solve everything else. No number of bits helps against reusing one password across several services, against a spoofed login page, or against a breach at the service itself. That is what unique passwords, a password manager and a second factor are for.
How many bits are enough depends on what the password protects. For an ordinary account, where the service limits the number of attempts, it matters far more that the password does not work anywhere else. For a password protecting encrypted data — a password manager vault, an encrypted disk, a backup — guessing runs offline and at full speed, and there it pays to go considerably higher.
The tool computes entropy from how the password was actually created: for random characters as length × log2(alphabet size), for a passphrase as word count × log2(dictionary size). Turn off a character group or leave out the look-alikes and the alphabet shrinks, so the number falls. Nothing is added for a password "looking complicated".
How to choose
Words or characters
Why a passphrase is often the better choice
For a password you have to know by heart — unlocking a password manager, signing in to a computer, an encrypted disk — randomly drawn words are almost always better than random characters. The entropy comes from the number of words, not from how odd the characters are. Words stick in your memory as an image, they can be read out over the phone, and you can type them on a phone or on somebody else's keyboard without switching layouts. A random run of characters with the same entropy is far harder to remember, and a password you cannot remember either ends up written on paper or gets simplified.
The machine has to draw the words
A sentence you make up is not a passphrase. You pick from the few hundred words that happen to come to mind, you put them in an order that makes sense, and you reach for names and dates from your own surroundings. The guessability of such a sentence is in a different league from words drawn from an openly published dictionary. That the dictionary is public does not matter at all: security rests on how many combinations there are, not on the attacker not knowing the word list.
Why length decides more than exotic characters
Every character added multiplies the number of options by the size of the alphabet. Widening the alphabet, by contrast, adds only a fraction of a bit, and only per character. An eight-character password put together from all 86 characters this tool offers has roughly 51 bits. A twenty-character password made of lower-case letters alone has roughly 94 — more than forty bits more, even though it contains not a single capital letter, digit or symbol. Rules of the "at least one special character" kind therefore change the strength of a password very little; what they reliably do is turn people into authors of passwords like Password123!.
What to use where
The vast majority of accounts you never have to remember, because a password manager holds them. There, let the tool generate the longest random characters you can and never look at them. Keep passphrases for the two or three passwords you really must know by heart, because without them you cannot get to the rest.
This tool's dictionary has 789 words, so one word adds 9,6 bits. That is less than the established Diceware-style lists of 7,776 words, where one word carries roughly 12.9 bits — a passphrase of the same number of words drawn from here therefore comes out weaker, and it is worth adding a word or two. The tool does not hide it: entropy is computed from the real number of words in the dictionary, not from some round figure.
How the generation works
Where the randomness comes from
On a password generator only one thing matters: the quality of the randomness, and the fact that picking a character does not favour part of the alphabet. Both can be done badly in a way that nothing about the result reveals.
01
Randomness from the system
The browser draws using crypto.getRandomValues, which takes its randomness from the operating system generator. The ordinary Math.random function is not used for passwords and must not be: it is fast but predictable, and from a handful of its outputs its internal state can be worked out.
02
Uniform selection
A random number cannot simply be reduced modulo the number of characters in the alphabet. The range of the number usually does not divide evenly by the number of characters, and characters at the start of the alphabet would come up slightly more often. The tool therefore throws away numbers from the leftover part of the range and draws again until it gets one from the part that divides exactly.
03
The entropy calculation
Entropy is computed from how the password was actually created: for characters as length × log2(alphabet size), for a passphrase as word count × log2(dictionary size). Options that draw nothing — a capital first letter on each word, say, or the separator — do not enter the calculation, because they add no randomness.
04
What stays with you
The generated password is not sent anywhere, is not written to browser storage and does not reach the page address, so you will not find it in your browsing history. Meanwhile the rest of the page behaves like any other on the web: our own traffic measurement starts only after you accept cookies, but the Google Analytics script loads regardless of consent whenever it is enabled on the site, so Google sees your IP address either way. None of that has anything to do with the generated password — it ends up in none of those requests.
The tool is no substitute for a password manager. Generating a good password is the easier part; the harder part is having a different one for every service and not having to remember them. Anyone who uses a password manager has the generator built into it and does not need this page.
A good password is cheap. The habit of a different one everywhere is the work.
The generator solves one password. Rolling out a password manager, a second factor and rules for accounts across the company is something a security assessment can work through.
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