Calculate Shannon entropy of text or data to measure randomness and information content in bits.
Entropy Calculator summarizes the frequency distribution of symbols in pasted text or data with Shannon's base-2 entropy formula. It reports the entropy of the observed symbol distribution in base-2 units. Repeated input falls to 0, while an even distribution across more distinct symbols scores higher. It does not determine whether the source was random or whether a secret resists guessing. That distinction is the common surprise. Because samples can be sensitive, the calculation stays in the browser and nothing is uploaded.
A concrete input and expected output from the current implementation.
Input
aaaa
Expected output
Shannon entropy: 0 bits per symbol
Only one symbol appears, so its observed probability is 1. The calculation is -(1 * log2(1)) = 0.
For an input containing N symbols, each distinct symbol's probability is its count divided by N. The Shannon value is H = -sum(p * log2(p)) over symbols that appear. A symbol seen every time has probability 1 and contributes 0; spreading observations evenly across several symbols increases H.
This is a zero-order frequency measure: it uses how often symbols occur, not the order in which they occur. With a base-2 logarithm, H is conventionally read as bits per observed symbol. For a sample of length N, N * H is a derived total under the same empirical, independent-symbol model, not automatically a security estimate.
No. This result describes the observed symbol frequencies in the pasted sample. It does not account for dictionaries, human choice, generator bias, known structure, attack strategy, or secret length in a complete security model. A predictable string can have balanced character counts. Evaluate secret strength from its generation process and plausible attacker guesses.
Shannon entropy calculated from single-symbol frequencies does not consider position. For example, ABAB and AABB each contain two As and two Bs, so both have entropy of 1 bit per symbol. If ordering and repeated sequences matter, use a higher-order or conditional analysis; this calculator's frequency result alone will not expose those patterns.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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