Password Strength Checker

A password's strength determines how long it would realistically take an attacker to guess it. This tool analyzes your password in real time, scoring it based on length, character variety, and whether it contains common patterns. Unlike tools that send your password to a server, this checker runs entirely in your ブラウザ—your password never leaves your デバイス.

What makes a password strong

Length is the most important factor. An 8-character password with all character types is fundamentally weaker than a 16-character password. Character variety matters too: passwords with uppercase, lowercase, numbers, and symbols are exponentially harder to crack than lowercase-only passwords. However, avoiding common words and predictable patterns (like "password123" or "123456") is equally critical—attackers try these first.

How the scoring works

The tool awards points for length milestones (8+ characters, 12+, 16+, 20+), character variety (uppercase, lowercase, numbers, symbols), and subtracts points if your password matches known weak patterns. The final score determines the rating: Very Weak, Weak, Fair, Strong, or Very Strong. Color coding helps you see at a glance whether your password is secure.

Actionable suggestions

Based on your password's weaknesses, the tool offers specific suggestions. If you're missing uppercase letters, it tells you to add them. If the password is too short, it recommends increasing length. If it detects common patterns, it warns you to avoid them. Use these suggestions to iteratively improve your password.

Best practices

For maximum security, aim for at least 16 characters with mixed character types. Avoid dictionary words, names, dates, and sequential patterns. Use a password manager to 生成 and store complex passwords so you only need to remember one strong master password. Never reuse passwords across different services.