Password Strength Checker
Free online password strength checker and security meter. Check password strength instantly, test if your password is strong, and estimate brute-force crack time without uploading any data.
Enter a password above and click "Test Your Password" (or select a quick test preset) to analyze password strength, dictionary vulnerabilities, and crack times.
Your Password Never Leaves Your Device
“This free password strength checker runs entirely in your browser using client-side JavaScript. Nothing you type is transmitted, stored, or logged.”
You can test this yourself: load this page, disconnect your Wi-Fi or internet connection, and run a password strength test. The tool will continue analyzing passwords offline with complete security and zero network traffic.
How Our Password Tester Checks Password Strength
Unlike legacy password complexity checkers that only check for capital letters or exclamation marks, our password strength meter evaluates actual mathematical resistance against modern brute-force cracking tools (like Hashcat and John the Ripper).
1. Password Length
Length is the single most critical factor when checking if a password is strong. Adding characters expands the search space exponentially rather than linearly.
2. Character Diversity
Combining uppercase letters (26), lowercase letters (26), numbers (10), and special symbols (33) expands the character pool (N) up to 95 possible characters per position.
3. Dictionary & Pattern Penalties
Attacker dictionaries target common words (e.g. "summer", "password"), years (e.g. "2025"), and character repetitions ("aaa"). Our algorithm detects these patterns and penalizes the score.
4. Bit Entropy Calculation
Measured in bits (H = L × log2(N)), entropy quantifies how many binary decisions an attacker must solve to guess the password by brute force.
Modern security standards (such as NIST SP 800-63B) emphasize that length contributes more to security than complexity. A long password composed of multiple random words or characters is far stronger than a short password with complex symbols.
Why Password Length Matters More Than Complexity
For decades, standard password policies forced users to create passwords like P@ssw0rd!1. These passwords are easy for computers to crack using masked dictionary attacks, yet extremely difficult for humans to remember.
When evaluating password security using a password tester, consider the math:
- A 10-character password with mixed characters yields approximately 59 bits of entropy.
- A 16-character password with standard lowercase letters and numbers yields approximately 83 bits of entropy.
- A 20-character password yields over 120 bits of entropy, making brute-force cracking mathematically impossible even with quantum computing supercomputers.
To learn more about how character lengths impact search space exponentiation, read our detailed guide on Password Length vs Complexity.
What Makes a Password Strong?
When you check password strength, a truly secure password possesses five core characteristics:
- Sufficient Length: At least 16 characters (or 20+ for critical accounts).
- High Randomness: Generated by a Cryptographically Secure Pseudorandom Number Generator (CSPRNG) or genuine random dice (Diceware).
- Uniqueness: Used exclusively for a single account and never shared across websites.
- Not Reused: Credential stuffing attacks automatically attempt leaked passwords across thousands of popular services.
- Free of Personal Data: Excludes names, birthdays, pet names, street names, or predictable numbers.
For a deeper exploration, read our full article on What Makes a Strong Password.
Password Strength vs Password Breach
People often confuse Password Strength with Breached Passwords. It is vital to understand that they measure two completely different security properties:
| Property | Password Strength | Breach Status |
|---|---|---|
| Definition | Mathematical resistance against guessing and brute-force cracking. | Whether the password has leaked in past third-party data breaches. |
| Evaluation Method | Calculated locally via character set entropy and pattern algorithms. | Cross-referenced against databases of compromised credentials (e.g. Have I Been Pwned). |
| Example Risk | A weak password (e.g. 123456) can be cracked in milliseconds even if not leaked. | A complex password (e.g. Tr0ub4dor&3) is useless if already leaked online. |
How Password Entropy Works
Information entropy is measured in bits. Each bit of entropy doubles the total number of attempts an attacker must execute to test all possible combinations.
- 40 bits: 240 (≈ 1.1 trillion) combinations. Vulnerable to basic online/offline attacks.
- 60 bits: 260 (≈ 1.15 quintillion) combinations. Secure against standard online attacks.
- 80 bits: 280 (≈ 1.2 septillion) combinations. Resists specialized offline GPU brute-force clusters for decades.
- 100+ bits: Exceeds the capabilities of modern computational physics. Mathematically unbreakable under current technology.
Learn more in our guide to Password Entropy Explained.
Frequently Asked Questions
Is this password strength checker safe?
Yes. Everything happens locally inside your browser using JavaScript. No passwords are transmitted to our servers or saved anywhere.
How does this password tester check password strength?
Our password strength checker evaluates information entropy in bits, character set diversity, length, and checks against dictionary words and predictable patterns to estimate resistance against brute-force attacks.
Does my password get uploaded?
No. Nothing you type is transmitted, stored, or logged. You can verify this by opening your browser's Network tab or by disconnecting your internet connection before testing your password.
Is this better than checking against leaked passwords?
No. Strength and breach status are different things. Password strength measures mathematical resistance against guessing attacks, whereas breach checking verifies if your password appeared in past data dumps. A password must be both strong and unbreached.
Can a strong password still be compromised?
Yes. Even a high-entropy password can be compromised if you reuse it across multiple websites, fall victim to phishing attacks, or if your device is infected with malware keyloggers.
What entropy level makes a password strong?
Generally, 60+ bits of entropy is strong for basic accounts, while 80+ bits is considered excellent for banking, email master passwords, and root credentials.