Bits of entropy
50 over
130 bits. 20 characters from an alphabet of 90.
An attacker guessing offline at 100 billion a second would take longer than the universe has existed on average.
That rate is the assumption, and it is stated because “ centuries” means nothing without one. It describes somebody who already has the password database and a fast machine. It is not a guess at your own attacker; it is the hard case to plan against.
RANDOM -> PASSWORD · Local tool
Password Generator
Generate a random password or passphrase, and see the strength in bits.
Last updated
How strong does a password actually need to be?
Strength is measured in bits, and each bit doubles the number of guesses an attacker needs. At a hundred billion guesses a second, which is a reasonable figure for an offline attack on a leaked database, 60 bits falls in a few months and 80 bits does not fall. filetity generates passwords from the operating system's own randomness inside your browser, discarding the bytes that would make some characters more likely than others, and shows the bits as you change the length and the character sets rather than a badge saying strong. Six random words from a 256 word list is 48 bits and typeable by hand; twenty random characters is 131 bits and belongs in a password manager.
01 / Your device
the file stays here
02 / Browser memory
the work runs locally
03 / Back to you
saved on this device
When you would use this
Situations, not settings.
- A site that just told you your password was breached
- The one thing that has to change is that the new one is not a variation of the old one. Random characters from the system's own randomness cannot be a variation of anything.
- A password you have to read out or type on a TV
- Six random words are easier to say down a phone line than sixteen symbols, and still take longer to guess than most of what people choose.
- Setting up a router or a shared machine
- Older hardware often refuses symbols or caps the length. Turning a character set off shows what it costs in bits, so you can add length to make it back.
How it works / no cloud
A conversion engine, not an upload form.
Every character comes from crypto.getRandomValues, which is the operating system's own randomness rather than Math.random. Turning those bytes into characters is where most generators go wrong: taking a byte modulo the alphabet size makes the first few characters of the alphabet more likely than the rest, because 256 does not divide evenly by 26 or by 94. Bytes that would land in the uneven tail are thrown away and redrawn instead, so every character is exactly as likely as every other. The strength is then arithmetic rather than opinion: length times the log of the alphabet size, in bits.
- Offline ready
- Installable app
- No file limit queue
Straight answers
No accordion. Nothing hidden.
- Is it free?
- Yes, with no watermark and no page limit.
- Does it need an account?
- No. There is no account system.
- Is my file processed on my device?
- Yes. The file is read by your browser and never uploaded. There is no server to send it to.
- What formats are supported?
- Nothing goes in. Out comes a password of 6 to 64 characters, or a passphrase of 3 to 12 words.
- What are the limits?
- No limit worth naming. Ten at a time if you need a batch, and none of them is stored, logged or recoverable once the page is closed.
- Does it work on mobile?
- Yes, on any modern mobile browser. Large files are limited by the memory the phone gives the browser.
- Does it work offline?
- Yes, once the page has loaded. The tool keeps working with no network connection.
- What is a bit of entropy, and why not just say strong?
- Bits count how many guesses it takes. Each bit doubles the work, so 40 bits is a trillion guesses and 80 bits is a trillion times that. Strong is a rule about shape: a capital, a digit, a symbol. A twelve character password that passes every one of those rules is 71 bits, and six random words that pass none of them is 48 bits and far easier to remember. The rules describe what a password looks like; the bits describe how hard it is to find.
- Is a passphrase actually safe, if the words are ordinary?
- Yes, as long as the words are chosen randomly and there are enough of them, and the second half is where most generators quietly cheat. This list holds exactly 256 words, so each one is exactly 8 bits: ten words is 80 bits, and six words would be 48, which falls in about twenty three minutes at the attacker rate this page states. So the default is ten. Diceware needs only six because its list is 7,776 words. A short list is not weaker, it is longer for the same strength, and the number is on screen either way. What is genuinely unsafe is a phrase you invented yourself, because a phrase a person thought of is not random.
- Is the password sent anywhere, or saved?
- Neither. It is generated in the page and lives in the tab until you close it. There is no server here to send it to and no storage to write it into, which is checkable: open the network tab while you press the button and nothing goes out. Copying it puts it on your clipboard, which is the one place it does leave this page.
- Should I turn off symbols?
- Only when something refuses them, and plenty still does: bank sites, old routers, and anything that will be typed on a TV remote. Dropping symbols costs about a fifth of the strength per character, so add three or four characters to the length and you are back where you were. That is the trade the meter is showing while you toggle it.
Keep working locally
3 available · more coming