Password Strength Checker

Understanding the Basics

Password strength is a measure of how resistant a password is to guessing attacks — both automated (brute-force, dictionary, hybrid) and targeted (using personal information about the owner). Traditional password strength meters counted character categories (uppercase, lowercase, digits, symbols) and length to produce a score, but this approach is easily gamed: "P@ssw0rd1!" scores highly on character diversity but is one of the most commonly used weak passwords. Modern password strength analysis, pioneered by work from Carnegie Mellon University and implemented in libraries like zxcvbn (developed at Dropbox), takes a fundamentally different approach: it checks the candidate password against an extensive database of common passwords, names, dictionary words, keyboard patterns (qwerty, 12345), common substitutions (@ for a, 0 for o), date patterns, and repeats. The strength score is based on estimated guesses-to-crack rather than character composition. Entropy is measured in bits: a password with 40 bits of entropy would require 2^40 ≈ one trillion guesses on average to crack. The NIST SP 800-63B guidelines (2017) de-emphasize composition rules (mandatory capitals, digits, symbols) in favor of length, checking against known-breached password lists, and not requiring periodic rotation.

How to Use the Tool

1. Type a password into the input field (the password is never transmitted — all analysis is local).
2. The strength meter updates in real time as you type, showing a score from 0 (terrible) to 4 (very strong).
3. The analysis panel explains why the password is weak or strong: common patterns, dictionary matches, and estimated crack time are shown.
4. Crack time estimates are shown for different attack scenarios: online attack (1,000 guesses/sec) and offline fast hash attack (10 billion guesses/sec).
5. Suggestions for improvement are provided (increase length, avoid patterns, avoid dictionary words).

Key Features & Specifications

• Powered by zxcvbn — the industry-leading pattern-based password strength estimator developed at Dropbox
• Detects common passwords, dictionary words, names, keyboard patterns, dates, and l33t-speak substitutions
• Displays estimated crack time at multiple attack speeds (online throttled, offline slow hash, offline fast hash)
• Provides actionable feedback explaining exactly why the password is weak and how to improve it
• Visual entropy display in bits alongside the 0–4 strength score

Frequently Asked Questions (FAQ)

Q:Is my password sent anywhere when I type it here?

No. The entire strength analysis runs locally in your browser using the zxcvbn JavaScript library. Your password is never transmitted to any server. The tool is safe to use with real passwords for testing purposes.

Q:Why does a long password of random words score higher than a short complex one?

This is the principle behind passphrases (XKCD #936: "correct horse battery staple"). A random four-word passphrase has much higher entropy than an 8-character complex password because the search space is larger — even though the passphrase may look simpler. Length beats character complexity for true security.

Q:What makes a password truly secure?

Security best practice: use a passphrase of 4+ random words (diceware), a completely random string of 16+ characters, or a generated password from a trusted password manager. Avoid dictionary words, names, dates, and predictable substitutions regardless of how "clever" they seem.