String Entropy Calculator
Measure Shannon entropy and estimated strength in bits for any string.
How random is your string?
Entropy measures unpredictability, and it has two useful readings for a string. Shannon entropy looks at how varied the actual characters are, while a character-set estimate models how hard the string would be to guess as a password.
A repeated string like "aaaa" has near-zero Shannon entropy, while a mixed passphrase scores much higher. The set-based estimate, length times bits per symbol, is the number password checkers quote.
Two views, kept private
Both figures are computed in your browser from the text you type, so nothing is uploaded and you can safely analyse sensitive strings.
Frequently Asked Questions
What is Shannon entropy?
A measure of unpredictability per character based on how often each character appears. Repetitive text has low entropy; varied text has high entropy.
How is the strength estimate different?
It multiplies the length by the bits per character of the detected character set (lower, upper, digits, symbols) — the model used to gauge password strength.
Is my text uploaded?
No. Both measures are computed in your browser and nothing you enter is stored or sent anywhere.
Browse the full set of free, private, in-browser tools.