Frequency decoder
Analyze letter frequencies and test a substitution table letter by letter.
Paste an encrypted message, inspect the most frequent letters, place your guesses in a substitution table, and watch the decrypted preview update live.
Encrypted text
0 source chars
Decrypted preview
Substitution table
Available letters
Frequency hints
| Encrypted letter | Frequency | Likely letters |
|---|
Quick explanation
Letter frequency gives useful clues for breaking a simple substitution. Prefill the table with common English frequencies, then adjust the mappings until the message becomes readable.
Try this too
Need a simple count without a replacement table?
Use Letter frequency to count alphabetic-character occurrences and percentages without building a decoding hypothesis.
Additional information
How to use the frequency decoder
This decoder helps solve messages encrypted with a simple substitution. It does not magically find the perfect answer: it gives you frequencies, hints and a practical replacement table to test your guesses.
Encrypted text
Paste the message to analyze. Accented letters are normalized so the tool can work on the A-Z alphabet.
Progressive substitution
Unknown letters appear as _. As soon as you map an encrypted letter to a plain letter, the preview updates.
Hints, not certainties
A very frequent letter may be E, T, A or O in English, but context is still needed to confirm the solution.
Reading the frequencies
| Step | What you observe | Useful action |
|---|---|---|
| 1 | The most frequent letters in the encrypted text. | Compare them with common English letters: E, T, A, O, I, N... |
| 2 | Short words, repetitions and double letters. | Try simple guesses, then correct the table if the output becomes inconsistent. |
| 3 | The partially decrypted text. | Underscores mark unknown letters. Fill the table progressively. |
Try these too
To only measure percentages, use Letter frequency. To build a key without statistical analysis, try Simple substitution, Alphabet checker or Random alphabet.
Limits and reuse
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