01 / REPLACE
One letter, one partner.
A substitution alphabet is a rearrangement of A–Z. Every A gets the same replacement, wherever it appears. Read the mapping backwards to decrypt.
SAME PATTERNS. NEW LETTERS.
A secret alphabet.
Swap every letter for another. Then turn detective: count the characters, spot the patterns, and piece the message back together.
01 Make a secret
Enter each letter A–Z once. The first replaces A, the second replaces B, and so on.
A–Z becomes uppercase. Spaces, numbers, and other characters stay as written.
CIPHERTEXT
02 The deciphering desk
Paste any simple substitution cipher. Letter counts update as you type. Only A–Z letters are counted.
Follow the frequency
CiphertextTypical English
The guide shows the usual English frequency of the letter in that row. Compare the overall shapes; a cipher letter’s identity is still unknown.
| Letter | Count | Share | Frequency comparison | English |
|---|
Spot repeated sequences
Counts include overlaps: AAA contains AA twice. By default, sequences stop at any character outside A–Z. Joining removes those separators first. Share is the percentage of all counted sequences of the chosen length.
Whole words are sequences separated by spaces, tabs, or line breaks, of any length. Letter case is ignored for A–Z. Punctuation stays part of the word, so THE and THE, are counted separately. Share is the percentage of all word occurrences.
| Sequence | Count | Share | Your guess |
|---|
No sequences yet. Try a longer message, a shorter sequence length, or joining letters across separators.
Try a letter, reveal a word
Under each cipher letter, enter your plaintext guess. Reusing a guess swaps its previous assignment so the alphabet stays one-to-one.
Frequency guesses are a rough starting point, especially with short messages. They are not an automatic solution.
YOUR PARTIAL PLAINTEXT
Click a letter or dot to select its guess box, then type a replacement. Backspace clears it. Every matching letter updates. Keyboard: arrow keys navigate; Enter edits.
Where should I start?
Common English letters include E, T, A, O, I, and N. Try frequent letters first, then look for short words such as A, I, THE, and AND.
A repeated cipher letter always stands for the same plaintext letter. Double letters and repeated word shapes can help you test a guess. Use the surrounding sentence to check it.
Longer samples usually give more useful frequencies. Names, unusual topics, and other languages can have very different patterns.
02 / COUNT
The pattern survives.
Changing the letters preserves how often they appear, word lengths, and repeated letters. Those traces give a decipherer somewhere to start.
03 / EXPERIMENT
Let the words guide you.
Frequency is a clue, not proof. Combine counts with word patterns and revise your guesses. This classic cipher is for learning, not protecting real secrets.