password-entropy-meter 1.0.0

Tiny zero-dependency library to estimate password entropy (bits), character-set composition and a strength label.

password-entropy-meter

Tiny, zero-dependency Python library to estimate password entropy (in bits), character-set composition, and a strength label.

⚠️ Character-set entropy is a theoretical upper bound. It overstates the strength of human-chosen passwords (dictionary words, P@ssw0rd!-style patterns). For realistic guess estimation, use a model such as zxcvbn. Use this for quick checks and education.

Install

pip install password-entropy-meter

Usage

from password_entropy_meter import estimate, entropy_bits

estimate("correct horse battery staple")
# {'length': 28, 'charset': 26, 'bits': 131.6, 'strength': 'very strong'}

estimate("P@ssw0rd!")
# {'length': 9, 'charset': 95, 'bits': 59.1, 'strength': 'reasonable'}  # but trivially guessable in practice

entropy_bits("hunter2")   # 32.9

Why length beats complexity

Each extra random character multiplies the search space; composition rules add entropy only once. A random multi-word passphrase reaches very high entropy that is actually realised, because the words are chosen randomly. See a browser-based checker (entropy + breach exposure) at PwdFortress.

API

• entropy_bits(password) -> float — bits = length * log2(charset_size)
• charset_size(password) -> int
• estimate(password) -> dict — {length, charset, bits, strength}

License

MIT