How to generate and check bcrypt hashes
- Type a password and choose a cost factor. 10 to 12 is typical for web applications today.
- Press Hash. The result, starting with
$2a$or$2b$, includes the version, cost and a random salt, so it is all you need to store. - To test a login, paste a password and a stored hash into the checker. It tells you whether they match and shows the hash's settings.
About bcrypt
bcrypt is a password hashing function designed in 1999 by Niels Provos and David Mazières, based on the Blowfish cipher. Unlike fast hashes such as MD5 or SHA-256, it is deliberately slow, and the cost factor makes it slower still: each step up doubles the work. That barely matters for one login but makes guessing billions of passwords from a stolen database impractical. A random 128-bit salt is generated for every hash, so two users with the same password get different hashes and precomputed rainbow tables are useless.
Use this page to create test fixtures, seed an admin account, debug a login that fails, or learn how stored passwords work. Note that bcrypt ignores everything after 72 bytes of the password, and that newer applications may prefer Argon2id, the winner of the Password Hashing Competition. Hashes from PHP's password_hash ($2y$) are compatible. The work happens in your browser using the open-source bcrypt.js library, loaded on demand; nothing you type is transmitted.
Can a bcrypt hash be decrypted?
No. Hashing is one-way. The only attack is guessing passwords and hashing each guess, which bcrypt makes slow.
What cost factor should I use?
Choose the highest cost that keeps a login under about 250 ms on your server; for most that is 10 to 12 today.
Why is the hash different each time?
A new random salt is used for every hash. The checker still confirms the password, because the salt is stored in the hash.