Frequency analysis
Every language has a characteristic letter distribution. In English, E, T, A, O, I and N are the most common letters and J, X, Q and Z the rarest. That fact has broken simple substitution ciphers since the Arab scholar al-Kindi described the method in the ninth century: count the letters in the ciphertext, match the most frequent to E, and work outwards.
The table compares your text with standard English frequencies from Robert Lewand’s Cryptological Mathematics (2000). A Caesar-shifted text shows the same shape as English shifted along the alphabet; a transposition cipher keeps English frequencies exactly; a well-made modern cipher looks flat.
Other uses
- Word games and puzzles: see which letters are over-represented in a word list.
- Language identification: different languages have distinct profiles (Spanish is rich in E, A and O; German in E, N and I).
- Typography and keyboard design: frequency tables inform key layouts and font testing.
A–Z only folds accented letters into their base letter (é → e) and ignores other scripts. Turn it off to count every letter in any alphabet.
Worked example
Here is what the Letter Frequency Counter returns for its built-in example. Settings used: A–Z only (fold accents): on; Case-sensitive: off. Click Try an example in the tool above to load it, then change it as you like.
Wkh txlfn eurzq ira mxpsv ryhu wkh odcb grj. Iuhtxhqfb dqdobvlv euhdnv vxevwlwxwlrq flskhuv.| Result | Value |
|---|---|
| Letters counted | 77 |
| Distinct letters | 26 |
| Most common | H (9.1%) |
Questions
What is the most common letter in English?
E, at about 12.7% of letters in typical English text, followed by T (9.1%) and A (8.2%).
How do I use this to solve a cipher?
Paste the ciphertext and compare its most frequent letters with the English column. For Caesar ciphers, the Caesar Cipher tool can try all 25 shifts and rank them automatically.
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