Password Strength Tester - Free & Private

Test password strength with estimated crack time, entropy analysis, and pattern detection. Runs locally - your password never leaves your device.

Enter your password

Your password never leaves your browser. All analysis is performed 100% client-side.

About Password Strength Tester

This tool analyzes password strength using multiple factors: length, character variety, entropy (randomness), common pattern detection, and dictionary word checking. It estimates the time needed to crack the password using modern hardware.

Your password is analyzed entirely in your browser and is never sent to any server. For breach checking, only the first 5 characters of a hash are sent to the Have I Been Pwned API (k-anonymity), so your actual password is never exposed.

Password entropy measures randomness in bits. A truly random 12-character password using uppercase, lowercase, digits, and symbols has about 79 bits of entropy - enough to resist brute-force attacks for centuries with current hardware. However, patterns like 'Password123!' have far lower effective entropy because attackers try common patterns first.

Modern password attacks use dictionary lists, known breach databases, and rule-based mutations (appending numbers, replacing letters with symbols). The Have I Been Pwned database contains over 900 million compromised passwords. This tester checks your password against that database using k-anonymity - only the first 5 characters of the SHA-1 hash are sent, so your full password is never transmitted.

For maximum security, use a passphrase of 4-5 random words (e.g., 'correct horse battery staple') which is both strong and memorable, or generate a random password with the Password Generator and store it in a password manager. Avoid reusing passwords across sites - a breach on one site compromises all accounts sharing that password.

How the Password Strength Tester Works

01Type or paste your password into the input field
02The tool analyzes entropy, patterns, and common password databases
03See a strength score from weak to very strong
04Get specific suggestions to improve your password

What Makes a Password Strong

Password strength is measured by entropy - the number of possible combinations an attacker must try. A 12-character password using only lowercase letters has about 56 bits of entropy, while adding uppercase, numbers, and symbols pushes it past 78 bits. Length matters more than complexity: a 16-character lowercase passphrase like 'correct horse battery staple' is stronger than an 8-character complex password like 'P@s5w0rd'. Modern password crackers can test billions of hashes per second, so passwords under 10 characters are vulnerable regardless of complexity. Use a password manager to generate and store unique passwords for every account.

When to Use the Password Strength Tester

Use this tool when creating new passwords for important accounts, when evaluating your organization's password policy requirements, or when teaching others about password security. It provides detailed feedback on why a password is weak and specific suggestions for improvement, unlike most registration forms that only show a basic strength bar.

Common Use Cases

Testing password strength before using it on important accounts → Strong Password Generator
Checking whether a password has appeared in known data breaches
Evaluating password policy requirements for an organization
Learning about password security through detailed entropy and pattern analysis

Expert Tips

Use a passphrase of 4-5 random words for passwords you need to remember - they are both strong and memorable.
Never reuse passwords across sites - use a password manager and generate unique random passwords for each account.
Enable two-factor authentication (2FA) wherever available - it protects your account even if the password is compromised.

Frequently Asked Questions

How is password strength calculated?→

Strength is evaluated using multiple factors: length, character variety (uppercase, lowercase, digits, symbols), entropy (mathematical randomness), pattern detection (keyboard sequences, repeated characters, dictionary words), and breach database checking. A truly random 12+ character password with mixed character types is considered strong.

Is my password sent to a server?→

Your password is never sent anywhere in full. All analysis happens in your browser. For breach checking, only the first 5 characters of a SHA-1 hash are sent to the Have I Been Pwned API (k-anonymity protocol). The server returns all hashes starting with those 5 characters, and matching happens locally - your actual password is never exposed.

Is a longer password always better?→

Length is the single most important factor, but not the only one. A 20-character password of all lowercase letters ('aaaabbbbccccddddeeee') is weaker than a 12-character random mix ('x7K#mP9$vL2@'). However, a 4-word passphrase ('correct horse battery staple') combines length with memorability and is very strong.

What is a passphrase and should I use one?→

A passphrase is a password made of 4-5 random words, like 'purple-elephant-dancing-sunset.' Passphrases are typically 20-30 characters long, making them extremely resistant to brute force, while being much easier to remember than a random string of characters. Use one for your most important accounts, especially your password manager's master password.

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