Tools / Frequency Analysis
Frequency Analysis
Paste ciphertext to see a letter-frequency chart and an auto-generated substitution mapping based on English frequency order. Correct any wrong guesses by editing the mapping cells — the decoded output updates instantly.
Paste ciphertext above. The tool will auto-map letters by frequency rank and let you correct mistakes.
How frequency analysis works
A monoalphabetic substitution cipher replaces each letter with a fixed substitute. Because the mapping never changes, the frequency distribution of letters is preserved. In English text, E appears roughly 12.7% of the time, followed by T, A, O, I, N, S, H, R, … If the most common cipher letter is X, it almost certainly represents E.
The tool auto-fills the mapping by ranking cipher letters by frequency and assigning them to English letters in frequency order. This first pass is usually 60–80% correct. Refine the remaining letters using context clues (short words, double letters, common patterns like “TH”, “THE”, “ING”).
Challenges solved with this tool: picoCTF 2022 -- substitution0, substitution1, substitution2.