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Letter Frequency Counter

Free letter frequency counter. Count how many times each letter (A-Z) appears in text, with optional case sensitivity, sorted by frequency. Great for frequency analysis and breaking substitution ciphers. Runs in your browser.

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Deep dive guides

A LITTLE CONTEXT · 4 MIN READLetter Frequency: The Count That Cracks Ciphers

All 9 related guides

What Word Frequency Reveals About Your Writing — How word and letter frequency counters work, what Zipf's law predicts, why the top of every list is function words, and how to edit from a ranked list.
Classical Ciphers: Caesar, ROT13, Atbash — and How Vigenère Beat Them All — How the classical ciphers work: Caesar shifts, ROT13 and Atbash as special cases, the frequency analysis that breaks them all, and the moving Vigenère key that stalled codebreakers.
Cracking a Caesar Cipher Without the Key — Why 25 shifts are always enough to try, how the chi-squared test ranks candidates against English letter frequencies, and where the method breaks down.
Reading Data Through Its Bytes — UTF-8 bytes, the printable/control/high-byte split, and Shannon entropy — what a byte distribution table reveals about any string.
Every Character Counts: Totals, Uniques, and Frequency Tables — One pass over a string yields three useful numbers — total characters, unique characters, and a frequency table ranked by count.
Letter Frequency: The Count That Cracks Ciphers — How letter frequency analysis works: counting A–Z only, the English ETAOIN profile, why short texts mislead, and how counts turn ciphertext into plaintext.
The Vigenère Cipher Explained: How the Rolling Keyword Shift Works — How the Vigenère cipher works: a repeating keyword gives every letter its own Caesar shift, with worked encrypt and decrypt examples and the real tool.
ROT13 Explained: The Shift That Is Its Own Decode Button — Half of 26 is 13: why one fixed shift both encodes and decodes, what letters survive untouched, and where ROT13 honestly belongs.
Atbash Explained: The Mirror Cipher Older Than Rome — A becomes Z, B becomes Y: the reflection table, why it is its own inverse, its Hebrew origins in Jeremiah, and why no key means no security.

How letter frequency counter works

Letter frequency analysis counts how many times each letter of the alphabet appears in a body of text. It is the classic technique for breaking monoalphabetic substitution ciphers (Caesar, Atbash, simple keyword ciphers): in English the most frequent letters are usually E, T, A, O, I, N, so the most frequent ciphertext letter is a strong candidate for E.

This counter scans your text and tallies only alphabetic letters (A-Z), ignoring digits, punctuation, spaces, and symbols. By default it folds case so 'A' and 'a' count together; toggle case sensitivity to count them separately. Results are sorted by count descending, with each letter's percentage of all letters shown.

Compare the resulting distribution against the known English letter-frequency profile to identify likely plaintext mappings when attacking a cipher, or use it for text analysis, stylometry, and language detection. All processing happens in your browser — no text is uploaded.

Frequently asked questions

What is letter frequency analysis?

A method for breaking substitution ciphers by counting how often each letter appears in the ciphertext. Because some letters are far more common than others in normal English (E is the most frequent), you can match the most frequent ciphertext letters to the most frequent plaintext letters.

Does this counter include numbers and punctuation?

No. Only the 26 letters A-Z are tallied. Digits, punctuation, spaces, and other symbols are ignored so the percentages reflect the true letter distribution.

What does the case sensitivity option do?

When off (default), upper and lower case letters are counted together, so 'A' and 'a' both add to the same tally. When on, they are counted as separate entries, useful for studying capitalization patterns.

Can this break any cipher?

Letter frequency analysis defeats simple monoalphabetic substitution ciphers (Caesar, Atbash). Polyalphabetic ciphers like Vigenère need additional techniques, and modern encryption is unaffected. Use it as a learning and puzzle tool.

Letter Frequency Counter

Deep dive guides

How letter frequency counter works

Frequently asked questions

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