How a Password Strength Checker Works
A password strength checker evaluates how secure your password is against brute-force attacks. This free tool analyzes your password's entropy — measured in bits — which tells you how many guesses an attacker needs to crack it. Higher entropy means exponentially more guesses required.
The formula is simple: entropy = length × log₂(character set size) . Character set size is the total pool of possible characters your password uses — 26 for lowercase only, 52 for lower and upper, 62 with numbers, up to 95 with symbols. Every character type you add multiplies the attacker's workload dramatically.
Raw entropy is just the baseline. This tool also applies a penalty when it detects common dictionary words, keyboard patterns like "qwerty" or "123456", or repeated characters — because attackers test these first using dictionary and rule-based attacks, not random guessing.
📊 Weak vs Strong Password
A strong password uses length and character variety to maximize entropy. The difference is massive: ~105 bits vs ~37 bits — that's 2⁶⁸ times harder to crack.
What the Crack Time Estimate Means
Crack time is estimated assuming an offline brute-force attack at 10 billion guesses per second — the realistic speed of a modern GPU password cracker. This is the worst-case scenario: an attacker who has already stolen a copy of your hashed password and is cracking it with no rate limiting.
Key Insight
A 12-character password using all four character types has roughly 78 bits of entropy — over 300 trillion trillion combinations. At 10 billion guesses per second, brute force alone would take longer than the age of the universe .
What Makes a Password Strong?
Genuine password strength comes from two sources: length and character variety . Length has the larger impact — each additional character multiplies total combinations by the entire charset size. A 16-character lowercase-only password is often stronger by entropy than an 8-character mixed-character password.
| Length | Charset | Entropy | Crack Time | Strength |
|---|---|---|---|---|
| 8 | 36 | ~41 bits | minutes | Very Weak |
| 10 | 62 | ~60 bits | hours | Weak |
| 12 | 95 | ~78 bits | millions of years | Fair |
| 16 | 95 | ~105 bits | billions of years | Strong |
| 20 | 95 | ~131 bits | > universe | Very Strong |
Common Password Mistakes to Avoid
Substituting letters with numbers ("p4ssw0rd") provides almost no security — attackers include these substitutions in their dictionaries. Starting with a capital and ending with digits ("Password1") follows a pattern so common it's tested first in every serious attack. Dictionary words, keyboard patterns, and repeated characters are all red flags that this password security checker will detect.
Is It Safe to Check My Password Here?
Yes. This tool runs entirely inside your browser using JavaScript. Your password is never transmitted to any server, stored in any database, or logged anywhere. You can verify this yourself by disconnecting from the internet and using the tool — it works exactly the same way, because there is no server involved. This is a true offline password strength checker .