Password Strength Checker
Analyze your password's strength with entropy calculation, crack time estimates, and detailed security analysis. Get actionable tips to create stronger passwords.
Enter a password above to see its strength analysis
About Password Strength Checker
A strong password is your first line of defense against unauthorized access to your accounts and personal data. This free online Password Strength Checker analyzes your password in real time, providing a comprehensive security assessment that includes an entropy score, estimated brute-force crack times, and a detailed character-composition checklist. Every calculation runs entirely within your web browser using JavaScript. Your password is never transmitted over the network, stored in a database, or logged anywhere, making it completely safe to test even your most sensitive credentials.
How Password Entropy Works
Entropy measures the unpredictability of a password in bits. The formula is based on the size of the character pool and the password length: entropy = length x log2(pool size). A password that uses only lowercase letters draws from a pool of 26 characters, while one that mixes uppercase, lowercase, digits, and special symbols draws from a pool of roughly 95 printable ASCII characters. Longer passwords with diverse character types produce higher entropy, which directly translates to more guessing attempts required to crack them. Security experts generally recommend at least 60 bits of entropy for everyday accounts and 80 or more bits for sensitive systems such as banking or email.
Understanding Crack Time Estimates
Our tool estimates how long it would take to crack your password under four common attack scenarios. Online throttled attacks are limited to about 10 guesses per second by rate limiters and CAPTCHAs. Unthrottled online attacks may reach 1,000 guesses per second against a poorly configured web service. Offline attacks against slow hash algorithms like bcrypt or Argon2 can attempt around 10,000 hashes per second, while fast algorithms like MD5 or SHA-1 on modern GPUs can exceed 10 billion guesses per second. The crack time shown is the average time needed to exhaust half the key space, giving you a realistic sense of how secure your password is against each threat level.
Common Password Pitfalls
Many people unknowingly weaken their passwords by relying on dictionary words, keyboard patterns such as "qwerty" or "123456," or simple substitutions like replacing "a" with "@." Attackers use dictionaries of leaked passwords containing hundreds of millions of entries, and pattern-based guessing rules that test these common tricks first. Repeated characters like "aaa" and sequential runs like "abcdef" also reduce effective entropy because they are trivially predictable. Our checker flags all of these issues and provides specific, actionable suggestions to strengthen your password.
FAQ
Q: Is it safe to type my real password into this tool?
Yes. All analysis is performed entirely in your browser using client-side JavaScript. No data is sent to any server, and nothing is stored or logged. You can verify this by disconnecting from the internet and confirming the tool still works, or by inspecting network traffic in your browser's developer tools.
Q: What makes a password "Very Strong"?
A password rated "Very Strong" typically has at least 80 bits of entropy. This usually means it is 16 or more characters long, contains a mix of uppercase and lowercase letters, digits, and special characters, and avoids dictionary words, common patterns, and repeated or sequential characters. Such a password would take billions of years to crack even with the fastest known hardware.
Q: How is entropy different from password length?
Length is only one factor. A 20-character password made entirely of the letter "a" has very low entropy because there is no randomness, while an 8-character password using random characters from the full ASCII set has much higher entropy. Entropy accounts for both the length of the password and the diversity of characters used, giving a more accurate measure of security than length alone.
Q: Should I use a password manager instead of memorizing passwords?
Absolutely. A password manager generates and stores unique, high-entropy passwords for every account, so you only need to remember one strong master password. This eliminates the temptation to reuse passwords across sites, which is one of the most common causes of account compromise. Our companion Password Generator tool can create strong random passwords ready to save in your manager.