What Is a Password Strength Tester?
A password strength tester is a security tool that evaluates how resistant your password is to various types of attacks. Unlike a simple password tester that only checks length, a comprehensive password strength test analyzes multiple dimensions of security: mathematical entropy (unpredictability), estimated crack time against brute-force attacks, common pattern detection, dictionary word analysis, and — with our tool — whether your password has appeared in known data breaches.
Our free password strength meter performs real-time analysis as you type, giving you instant feedback on your password's security level. The tool calculates password entropy using the formula E = L × log₂(N), where L is the password length and N is the character pool size. It then estimates how long a modern GPU farm running 10 billion guesses per second would take to crack your password through brute force.
What sets our password strength checker apart is the integrated data breach check powered by Have I Been Pwned. You can check if your password has been exposed in any of the 900+ million pwned passwords collected from known data breaches — all while maintaining complete privacy through the k-anonymity protocol. Whether you want to know how secure your password is, how strong your password is, or if it has been leaked online, this tool provides comprehensive analysis in one place.
How to Test Your Password Strength
Testing your password strength takes seconds. Follow these four steps to get a complete security assessment:
Enter Your Password
Type or paste your password into the input field. It's never sent to any server — all analysis happens locally in your browser using JavaScript.
View Strength Score & Entropy
Instantly see your overall strength score (0-100), entropy in bits, character pool size, and estimated crack time. The strength bar shows your password's security level.
Check Data Breach Status
Click the breach check button to query Have I Been Pwned. Using k-anonymity, only 5 characters of the SHA-1 hash are sent — your password stays completely private.
Review & Improve
Check the issues and strengths lists for specific feedback. Missing character types, common patterns, and dictionary words are flagged so you can create a stronger password.
How Secure Is My Password?
The question "how secure is my password" depends on several factors: its length, character diversity, randomness, and whether it has appeared in known data breaches. A password that looks complex to a human may still be weak if it follows predictable patterns or has been compromised in a breach.
Our password strength tester evaluates security through a scoring system from 0 to 100. The score combines length (up to 30 points), character diversity (up to 45 points for using uppercase, lowercase, numbers, and symbols), and deductions for detected issues like common patterns, dictionary words, and repeated sequences.
| Score | Level | Crack Time | Example |
|---|---|---|---|
| 0–20 | Very Weak | Instantly | 123456 |
| 20–40 | Weak | Minutes | password1 |
| 40–60 | Fair | Days to months | Summer2024! |
| 60–80 | Strong | Millions of years | xK9$mL2p#Q |
| 80–100 | Very Strong | Billions of years+ | vR7!kM3$bN9@qL5& |
Password Entropy Calculator — How It Works
The password entropy calculator measures the mathematical unpredictability of your password in bits. Entropy is calculated with the formula:
E = L × log₂(N)Where E = entropy in bits, L = password length, N = character pool size
The character pool size depends on which character types your password uses: lowercase adds 26, uppercase adds 26, numbers add 10, and symbols add 33 — totaling 95 possible characters when all types are used. A 16-character password using all character types has approximately 105 bits of entropy, which would require on average 2⁶⁴ guesses to crack.
How Safe Is My Password?
Wondering how safe your password is? Beyond entropy and length, a truly safe password must also not exist in any breach database. Even a seemingly complex password like "P@ssw0rd123!" scores well on character diversity but has been found in millions of data breaches. That's why our tool combines traditional strength analysis with breach checking — giving you the complete picture of how strong your password really is against both brute-force attacks and credential stuffing.
Password Data Breach Check — Have I Been Pwned
Our password leak check feature uses the Have I Been Pwned Pwned Passwords database — a collection of over 900 million unique passwords that have appeared in known data breaches. These pwned passwords come from breaches of major services like LinkedIn, Adobe, Dropbox, MySpace, and thousands of others.
When attackers obtain breached password lists, they use them in credential stuffing attacks — automatically trying each leaked password against thousands of websites. If your password exists in any breach database, it's effectively a known password and can be cracked instantly regardless of its complexity.
How k-Anonymity Protects Your Privacy
Your password is hashed with SHA-1 using the Web Crypto API in your browser. For example, "password" becomes "5BAA6...8FD8" (a 40-character hex string).
Only the first 5 characters of the hash (e.g., "5BAA6") are sent to the API. This prefix matches ~800-2000 different passwords — your specific one can't be identified.
The API returns all hash suffixes that match your prefix, along with breach counts. This response is cached by CDN for 31 days.
Your browser compares the remaining 35 characters of your hash against the returned suffixes locally. The full hash never leaves your device.
Has My Password Been Leaked?
If you're asking "has my password been leaked", use the breach check button above to find out. Common passwords like "password", "123456", or "qwerty" have been found in tens of millions of breaches. Even passwords that seem unique may have been exposed if you used them on a service that suffered a data breach. If your password is found, use our Password Generator to create a new, strong, unique replacement immediately.
Understanding Password Strength Levels
Our password strength tester classifies passwords into five security tiers based on their overall score. Each tier represents a different level of resistance to brute-force attacks, assuming an attacker with a modern GPU farm capable of 10 billion password guesses per second:
Can be cracked instantly. Includes common passwords, short passwords, single character types, and obvious patterns. These passwords offer essentially no protection.
Crackable in minutes to hours. Slightly better than common passwords but still vulnerable to basic dictionary and brute-force attacks. Missing critical character types.
Takes days to months to crack. Uses multiple character types but may be too short or contain detectable patterns. Adequate for low-value accounts but not recommended for important ones.
Would take millions of years to brute-force. Good length with diverse characters and no common patterns. Suitable for most accounts when combined with 2FA.
Billions of years to crack. Maximum length and character diversity with no detectable patterns or dictionary words. Ideal for critical accounts: email, banking, password managers.
Common Password Mistakes to Avoid
Our password audit tool detects several common mistakes that weaken passwords. Even experienced users sometimes fall into these traps. Here are the patterns our strength tester flags:
Using common English words ("password", "dragon", "admin") or their simple variations with number substitutions ("p@ssw0rd"). Attackers try dictionaries first.
Sequential keyboard patterns like "qwerty", "asdfgh", or "zxcvbn" are among the first combinations tested in brute-force attacks.
Number sequences ("123456", "654321") and letter sequences ("abcdef") are instantly guessable and offer zero security.
Repeated characters ("aaaaaa") or sequences ("abcabc") dramatically reduce the effective entropy of your password.
Passwords under 8 characters can be cracked in seconds regardless of complexity. NIST recommends at least 8 characters minimum, 16+ recommended.
Using only lowercase, only numbers, or only uppercase severely limits the character pool and makes brute-force attacks exponentially easier.
How Our Password Tester Ensures Privacy
Privacy is the foundation of any trustworthy password security checker. Our tool implements multiple layers of privacy protection to ensure your password remains completely confidential:
All strength analysis — entropy, patterns, dictionary checks, scoring — runs entirely in your browser using JavaScript. Your password is never transmitted to any server.
The breach check sends only 5 characters of the 40-character SHA-1 hash to the API. This 5-char prefix matches hundreds of different passwords, making yours unidentifiable.
SHA-1 hashing uses the browser's built-in Web Crypto API (crypto.subtle.digest), the same secure implementation used for TLS/SSL connections.
We don't log, store, or track passwords in any way. No cookies, no analytics on password content, no server-side processing. Close the tab and the data is gone.
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Frequently Asked Questions About Password Strength Testing
How is password strength calculated?
Strength is determined by: length (up to 30 points), character diversity — uppercase, lowercase, numbers, symbols (up to 45 points), and deductions for detected issues like common patterns, dictionary words, and repeated sequences. The final score ranges from 0 to 100.
What is password entropy?
Password entropy measures unpredictability in bits using the formula E = L × log₂(N), where L is length and N is character pool size. A 16-character password with all character types has about 105 bits of entropy. Below 40 bits is weak, above 80 is very strong.
How secure is my password?
Enter your password in the tester above to find out. The tool analyzes entropy, crack time, patterns, character composition, and data breach status. A score of 80+ means your password is very strong and would take billions of years to crack.
Is my password sent to any server?
No. All strength analysis runs in your browser. For the breach check, only 5 of 40 characters of the SHA-1 hash are sent using k-anonymity — it's mathematically impossible to determine your password from this prefix.
How does the breach check work?
Your password is hashed with SHA-1 locally. Only the first 5 hex characters are sent to the Have I Been Pwned API, which returns matching suffixes. Your browser checks locally if the full hash matches. Your password never leaves your device.
What are pwned passwords?
Pwned passwords are passwords exposed in known data breaches. The Have I Been Pwned database contains over 900 million unique passwords from breaches of LinkedIn, Adobe, Dropbox, and thousands more. Attackers use these in credential stuffing attacks.
Has my password been leaked?
Click 'Check if Password Has Been Leaked' after entering your password. If found in breaches, you'll see the breach count. Change it immediately on all accounts. Use our Password Generator to create a strong replacement.
How long would it take to crack my password?
Our calculator estimates crack time assuming 10 billion guesses per second (modern GPU farm). A 6-char lowercase password: instantly. A 12-char mixed password: ~3 million years. A 16-char all-types password: billions of years.
What makes a strong password?
Four key properties: sufficient length (16+ chars), character diversity (all types), true randomness (not based on words or patterns), and uniqueness (never reused). Also: not found in any breach database.
Should I change my password if it's been breached?
Yes, immediately. Change it on every account where you've used it. Attackers try breached passwords across thousands of sites. Use a password manager with strong, unique passwords for each account and enable 2FA.