Password generator
Passwords are created in your browser using its cryptographic random number generator. Nothing is sent anywhere, and the page keeps no record of what it makes.
How the numbers are worked out
Each character is chosen uniformly from the selected set using crypto.getRandomValues, with rejection sampling so that no character is more likely than another. Entropy in bits is the length multiplied by log₂ of the set size. In passphrase mode each word is drawn uniformly from a list of common English words built into this page, and the entropy shown is the word count multiplied by log₂ of the list size, which is about 9 to 10 bits per word. Because the list is short compared with a full dictionary, a passphrase needs more words than a character password has characters for the same strength. The strength labels are a rule of thumb for offline guessing of a leaked hash: under 40 bits is weak, 40 to 59 is fair, 60 to 79 is strong and 80 or more is very strong. A password is only as safe as the way it is stored, so use a different one for each site and keep them in a password manager.