Frequency Analyzer

Analyse letter frequency, the Index of Coincidence and common digraphs in a text — the core statistics for breaking classical substitution ciphers (Caesar, Vigenère). Compares observed percentages against standard English letter frequencies. Counts A–Z only, case-insensitive. Pure JS, in your browser.

Text (ciphertext or any text)

Letter frequency (observed vs English %)

Letter	Bar	Count	Obs %	Eng %

Top digraphs

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Index of Coincence IC = Σ fᵢ(fᵢ−1) / (N(N−1)). English ≈ 0.0667, uniform random ≈ 0.0385. Most meaningful for longer texts.