Letter Frequency Analyzer - Online ETAOIN SHRDLU

A Letter Frequency Analyzer is a tool that counts how often each letter (A–Z) appears in a given text. It displays the results as counts, percentages, and visual bars, making it easy to see which letters dominate your writing. This is useful for writers, cryptographers, linguists, word game enthusiasts, and anyone curious about letter distribution patterns in English or other languages.

ETAOIN SHRDLU represents the 12 most common letters in the English language, arranged in descending order of frequency: E, T, A, O, I, N, S, H, R, D, L, U. The name originated from Linotype typesetting machines, where these letters appeared in the first two vertical columns of the keyboard. Typesetters would sometimes run their fingers down these columns to fill out a line with filler text, and "ETAOIN SHRDLU" would appear in print by mistake. Today, it's a cultural reference in typography and a fundamental concept in cryptography and frequency analysis.

Letter frequency analysis is one of the oldest techniques for breaking substitution ciphers (like the Caesar cipher or simple monoalphabetic ciphers). In English, E is the most common letter (~12.7%), followed by T (~9.1%) and A (~8.2%). By comparing the frequency distribution of letters in an encrypted message to the known distribution of the suspected language, cryptanalysts can make educated guesses about which ciphertext letters correspond to which plaintext letters. While modern encryption is far more sophisticated, frequency analysis remains a foundational concept in cryptology and is still used in CTF (Capture The Flag) challenges and historical cipher breaking.

Based on analysis of large English text corpora (Oxford English Corpus, Google Books, etc.), the approximate frequencies are:

Note: The ETAOIN SHRDLU sequence covers the top 12: E, T, A, O, I, N, S, H, R, D, L, U.

Absolutely! Knowing letter frequencies can give you an edge in word games like Wordle, Scrabble, and crossword puzzles. For Wordle, the best starting words often contain high-frequency letters like E, A, R, O, T, L, S, N. Common starting words like "SLATE," "CRANE," "ADIEU," and "STARE" all leverage the ETAOIN pattern. In Scrabble, high-frequency letters (E, A, I, O, N, R, T, L, S, U) appear on more tiles, while rare letters (Q, Z, J, X) are worth more points. Use this analyzer to study which letters dominate in different types of texts — you might discover patterns that improve your game strategy!

Yes, letter frequency can vary noticeably depending on the genre, domain, and style of the text. For example, technical or scientific writing may use more X (in words like "axis," "index," "matrix") and Q (in "equation," "quantum," "query"). Legal documents might have more L and T due to frequent use of words like "shall," "statute," and "title." Fiction and casual writing tend to follow the standard ETAOIN distribution more closely. Short texts (like tweets or headlines) may deviate significantly from the norm due to small sample size. This is why frequency analysis works best on larger text samples — the more text you analyze, the closer it converges to the expected distribution.

This tool provides real-time, client-side analysis with complete accuracy for counting letter occurrences. All processing happens in your browser — no data is ever sent to any server, ensuring your text remains private and secure. The tool uses simple JavaScript to tally A–Z characters (case-insensitive) and calculates percentages based on total letter count. For most practical purposes — writing analysis, word game strategy, basic cryptography education, or linguistic curiosity — this tool is perfectly sufficient. Professional corpus linguistics tools may offer additional features like n-gram analysis, part-of-speech tagging, and statistical significance testing, which are beyond the scope of this lightweight analyzer.