Password Strength Checker
Check password strength with entropy analysis, character variety checks, and common password detection.
What Is a Password Strength Checker?
A password strength checker evaluates how resistant a password is to guessing and brute-force attacks. This tool analyzes your password across multiple dimensions: length, character variety (uppercase, lowercase, digits, symbols), Shannon entropy in bits, and whether the password matches known common passwords. The result is a strength rating from Very Weak to Very Strong, along with a detailed checklist so you know exactly what to improve.
How to Use the Password Strength Checker
- Type or paste your password into the input field.
- The strength meter and checklist update in real time as you type.
- Review the checklist to see which criteria your password meets.
- Toggle the eye icon to show or hide the password characters.
Features
- Real-time strength rating: Very Weak, Weak, Fair, Strong, Very Strong
- Visual 5-bar strength meter with color coding
- Entropy calculation in bits based on character set and length
- Checklist: length thresholds, uppercase, lowercase, digits, symbols
- Common password detection against a curated list
- Show/hide password toggle for easy review
- Runs entirely in your browser — no data is transmitted
FAQ
How is password strength calculated?
The checker scores passwords based on length (8+, 12+, 16+ characters), character variety (uppercase, lowercase, digits, symbols), and whether the password appears in a list of commonly used passwords. Entropy (bits) is also calculated from the character set size and password length.
What is password entropy?
Entropy measures how unpredictable a password is, expressed in bits. It is calculated as log2(charset_size) × length. A password with 60+ bits of entropy is generally considered strong; 80+ bits is very strong.
Is my password sent to a server?
No. All analysis runs entirely in your browser using JavaScript. Your password never leaves your device.
What makes a strong password?
A strong password is at least 12 characters long, mixes uppercase letters, lowercase letters, digits, and symbols, and does not appear in common password lists. Using a passphrase of 4+ random words is also an effective strategy.