EntropyBolt
Generate a password or a passphrase, see exactly how many bits your settings are worth, and check an existing one against the patterns that make it guessable. Everything runs in this tab.
Options
Advanced
Alphabet in use: 90 characters
Generate a batch
Password Strength
N/AHow it works
- 1
Pick characters or words
A random string, or a passphrase built from a 2,307-word list.
- 2
Set the length and the alphabet
Every change updates the exact entropy before you commit to it.
- 3
Read the real numbers
Bits computed from your settings, and crack times for four attack scenarios.
- 4
Copy it into a password manager
Generate one, or a batch of up to 50 as a text file.
What it actually does
Cryptographic randomness
Every character comes from crypto.getRandomValues with rejection sampling, so no character is likelier than another.
Entropy that is actually exact
Bits are derived from your settings, not guessed from the output, so the same settings always report the same strength.
Passphrases you can type
Six words from a 2,307-word list is 67 bits — strong and still memorable.
Tells you what is weak
Test a password and see which patterns cost it bits: sequences, repeats, a trailing year, a leaked entry.
Batches of up to 50
Generate a list at once and download it as a plain text file.
Never leaves the tab
No network requests, no storage, no analytics on what you type. Works with the connection off.
Frequently Asked Questions
Is anything I generate or type sent to a server?
No. There is no network request of any kind. Nothing is stored either — not in localStorage, not in a cookie — so closing the tab leaves no trace.
How is the entropy calculated?
For a generated password it is exact: length × log2(alphabet size), using the alphabet your settings actually produce, exclusions included. For a passphrase it is words × log2(list size). For a password you type in, it can only be estimated, so patterns like sequences, repeats, a trailing year or an entry from a breach list are deducted and shown itemised.
Are the generated passwords really random?
They come from crypto.getRandomValues, the browser cryptographic generator. Values outside an exact multiple of the alphabet size are discarded and drawn again, so every character is equally likely — taking the remainder directly would quietly favour the first few characters of the alphabet.
Why four different crack times?
Because a single figure is misleading. Ten billion guesses a second only applies if an attacker has the password database and it uses a fast hash. Against a real login form it is nearer a hundred a second, and against a properly configured slow hash, thousands. The same password can be unbreakable in one column and gone in another.
Is a passphrase weaker than a random password?
Per character, yes. In total it depends on the word count: six words from the 2,307-word list is 67 bits, which beats a random 10-character password. The advantage is that you can type it from memory on a phone, and the number on screen tells you exactly what you are getting.