Password Strength Checker (Python)

Overview

After building a password strength checker with HTML, CSS, and JavaScript, I wanted to create a Python version that feels more like a small security utility.

This project checks passwords based on length and character variety, but also compares them against a local wordlist of common passwords. That makes it a bit more practical than a checker that only looks for uppercase letters, numbers, or symbols.

Features

• Built in Python as a command-line tool
• Checks for minimum length, lowercase and uppercase letters, numbers and symbols
• Compares passwords against a local common-password wordlist
• Gives simple feedback and improvement suggestions

Why I built it

I wanted to build a second version of the password checker in Python because I wanted to include the possibility of comparing passwords to a local wordlist.

Instead of only checking whether a password looks complex I wanted to include the idea that a password can still be weak if it is common or reused.

Example Output

Password check

Snippets from the key code

Password evaluation (rules + score)

def evaluate_password(password: str, common_passwords: set[str]) -> dict:
"""Evaluate password strength and return detailed results."""
checks = {
  "length": len(password) >= 12,
  "lowercase": bool(re.search(r"[a-z]", password)),
  "uppercase": bool(re.search(r"[A-Z]", password)),
  "number": bool(re.search(r"[0-9]", password)),
  "symbol": bool(re.search(r"[^A-Za-z0-9]", password)),
  "common_password": password.casefold() in common_passwords,
}

score = 0
for key in ["length", "lowercase", "uppercase", "number", "symbol"]:
  if checks[key]:
    score += 1
    
    if checks["common_password"]:
      score = max(score - 2, 0)
      
      if checks["common_password"]:
        strength = "Weak"
        elif score <= 2:
        strength = "Weak"
        elif score == 3:
        strength = "Okay"
        elif score == 4:
        strength = "Strong"
        else:
          strength = "Very strong"
          
          return {
            "checks": checks,
            "score": score,
            "strength": strength,
          }

What I learned

This project was a nice way to practice Python with something small but still useful.

One part I liked was adding the local wordlist check, because it makes the tool more realistic than just checking for uppercase letters, numbers and symbols. A password can look “strong” at first glance and still be weak if it is common or predictable.

It was also a good reminder that even simple tools can become much more useful when they give clear feedback and are easy to adapt.

Links

🔗 View Source Code on Codeberg and try it yourself!

The script loads its passwords from a local wordlist file, so feel free to use other common-password or custom wordlists!