Frequency Analysis
Paste ciphertext to inspect letter frequencies, repeated patterns, common bigrams and trigrams, word shapes, index of coincidence, and a best-guess decoded output.
Ciphertext input
Decoded guess
Using This Tool: Guide & Notes Show guide
Frequency Analysis inspects ciphertext for statistical clues such as letter counts, repeated groups, word shapes, and likely Caesar shifts.
How to use it
- Paste ciphertext into the input box.
- Start with Decode guess if you suspect Caesar, ROT13, or another rotation.
- Use Letters to compare observed letter counts with common English frequencies.
- Use Patterns to inspect repeated bigrams, trigrams, words, and word shapes.
Options and settings
- Top limit controls how many frequency and pattern results are shown.
- Strip accents normalises accented text before analysis.
- Repeated only hides one-off patterns so repeated clues stand out.
- Include single letters controls whether one-letter words are listed in pattern analysis.
Notes
- Longer samples produce more reliable statistics.
- The decode guess is designed for Caesar-style shifts, not modern encryption or full substitution solving.
Related Article
Frequency Analysis: The Statistical Fingerprint That Broke Classical Ciphers
How counting letters turned cryptanalysis from educated guesswork into a science, and why weak ciphers still betray themselves through the shape of language.