Password Strength Checker & Generator — Free Online Tool
Check how strong your password is and generate secure passwords instantly. See real-time feedback on entropy, crack time, breach status, and common pattern detection. Nothing is stored or transmitted. 100% client-side — passwords never leave your browser.
How to Use the Password Strength Checker
- Type or paste a password in the input field — strength updates in real-time.
- Read the strength meter — it shows entropy bits, crack times at different attack speeds, and breach status.
- Review suggestions to improve weak passwords before using them.
- Use the random generator to create a secure password with custom character options.
- Try the passphrase generator to create memorable, strong passphrases from random words.
Why Use This Password Strength Checker
"Password123!" looks strong to a human — it has uppercase, lowercase, numbers, and a symbol. But it's in every password dictionary and would be cracked in milliseconds. This tool uses entropy analysis, dictionary detection, keyboard/sequential pattern detection, and the Have I Been Pwned breach database to give you a realistic assessment, not just a checklist.
It's essential for security audits, user registration flows, and personal password hygiene. The generator creates truly random passwords that are both strong and memorable when you use the passphrase option.
How It Works — Entropy & Crack Time
Password strength is measured in entropy bits — a mathematical representation of how many possible combinations an attacker would need to try.
The formula is: entropy = log₂(pool_size^length), where pool_size is the number of unique characters available (e.g., 26 for lowercase letters,
62 for upper+lower+digits, 94 for all printable ASCII).
Crack time estimates are calculated by dividing the total search space by assumed attack speeds:
- Online attack (1K attempts/sec) — typical of a rate-limited web login. Even weak passwords survive longer here.
- Offline slow (10B/sec) — a single GPU cracking a salted hash. Represents a targeted attack on one account.
- Offline fast (100B/sec) — multiple GPUs or a dedicated cracking rig. Best-case scenario for attackers.
The tool also checks your password against a dictionary of common passwords, detects keyboard patterns (like "qwerty"), sequential characters (like "abcd"), and looks up the password in the Have I Been Pwned breach database using a privacy-preserving k-anonymity approach.
Password Strength Levels
Use this reference to interpret the strength meter:
| Level | Entropy | Description |
|---|---|---|
| Very Weak | < 28 bits | Cracked instantly — dictionary words, short passwords, common patterns |
| Weak | 28–35 bits | Minutes to hours — short with some complexity but still guessable |
| Fair | 36–59 bits | Days to years — decent for low-value accounts, but not for banking or email |
| Strong | 60–127 bits | Centuries to heat-death-of-universe — suitable for all accounts |
| Very Strong | 128+ bits | Mathematically uncrackable within the lifespan of the universe |
Tips for Creating Strong Passwords
- Length beats complexity — a 20-character lowercase passphrase is stronger than an 8-character password with symbols.
- Use the passphrase generator — 4+ random words create a strong, memorable password without memorizing random characters.
- Avoid personal info — birthdays, names, pet names, and addresses are in cracking dictionaries.
- Skip common substitutions — "P@ssw0rd" is in every dictionary; attackers replace letters automatically.
- Generate unique passwords for every site — a breach on one site won't compromise your other accounts.
- Check breach status — if your password appears in the HIBP database, change it immediately regardless of strength.
- Use a password manager — let it generate and store strong passwords so you only need to remember one master password.
Security Notes
- Never reuse passwords — credential stuffing attacks use leaked email/password pairs across thousands of sites. One breach can cascade.
- Enable two-factor authentication (2FA) — even a strong password can be phished. 2FA adds a critical second layer.
- Change passwords after breaches — if a service you use announces a breach, update your password there and anywhere you used the same one.
- Be cautious with security questions — answers like "mother's maiden name" are often guessable or findable on social media.
- Don't store passwords in plain text — use a reputable password manager rather than notebooks, sticky notes, or unencrypted files.
- This tool runs 100% client-side — your passwords are never transmitted. The HIBP check uses k-anonymity (only a hash prefix is sent).
Frequently Asked Questions
Length is the most important factor — a 20-character password with mixed characters has billions of years of crack time, even with brute force. Beyond length: use a mix of character types, avoid dictionary words and common patterns (like "password123" or "qwerty"), and never reuse passwords across sites. Also check it against breach databases.
It uses the Have I Been Pwned k-anonymity API: your password is hashed with SHA-1, and only the first 5 characters of the hash are sent to the API. The API returns all hash suffixes matching that prefix — the check happens entirely in your browser. Your actual password is never transmitted.
Entropy measures password strength in bits using the formula: log2(pool_size^length). The pool size depends on character types used (26 lowercase, 52 upper+lower, 62+numbers, 94+symbols). More entropy = harder to crack. 80+ bits is considered strong; 128+ is excellent.
Absolutely. Use this tool to generate a strong master password (20+ characters), then let a password manager generate and store unique passwords for every account. You only need to remember one strong password. Password managers are the single most impactful security improvement for most people.
Yes — passphrases like "correct-horse-battery-staple" are both strong and memorable. They work because of length (4 words = 40+ characters) rather than complexity. Use 4-6 random words from a large wordlist for maximum security with minimum memorization effort.
Use Cases
Testing Password Strength
Check password strength before creating accounts to ensure your credentials are secure.
Breach Detection
Check if your password appears in known data breaches using the Have I Been Pwned database.
Secure Password Generation
Generate cryptographically secure random passwords with customizable length and character types.
Memorable Passphrases
Create strong, memorable passphrases using random words for easy-to-remember security.
Auditing Team Policies
Verify that team password policies meet security standards and compliance requirements.