What does it do?
It generates the bcrypt hash of a password with the cost factor you choose, and checks whether a password matches an existing bcrypt hash — for example, one copied from your users table while debugging a login.
bcrypt runs in your browser with bcryptjs. Passwords are not stored, not put in the URL and never sent anywhere.
Anatomy of a bcrypt hash
$2b$10$WDHsS2e05u6fibtdF4fGpOLaoZCbgsENgQwk5ytDhrADLa89sOyYa
│ │ └──────── salt (22) ───────┘└──────── hash (31) ────────┘
│ └ cost: 2^10 = 1024 rounds
└ version
Limits
bcrypt only uses the first 72 bytes of a password. Longer passphrases, or text with many multi-byte characters, are silently truncated; the tool warns you when that happens.
Frequently asked questions
›Which cost should I choose?
The highest your servers can afford, usually so that one hash takes around 100–300 ms. Today that is often a cost of 10 to 12. Each step doubles the time, for you and for an attacker.
›Why does the same password give a different hash every time?
Because bcrypt generates a random salt for each hash and stores it inside the hash itself. That is why you compare with bcrypt.compare instead of hashing again and comparing strings.
›What do $2a$, $2b$ and $2y$ mean?
They are revisions of the format that fixed bugs in some implementations. They are compatible for normal passwords; $2b$ is the current one.