Caesar Cipher
Type a message, choose a shift and encrypt or decrypt it, or list all 25 shifts to crack it.
| Shift | Text |
|---|
What this tool does
A Caesar cipher replaces each letter with the one a fixed number of places further along the alphabet. With a shift of 3, A becomes D and "Hello" becomes "Khoor". Type your text, choose the shift and direction, and read the result. Tick "Show all 25 shifts" to decode a message when you do not know the key.
Shifts every letter by the number you choose, wrapping from Z back to A.
Optionally lists the result of all 25 shifts so you can spot the readable one.
How to use it
- Type or paste your text.
- Choose Encrypt or Decrypt and set the shift.
- Read the result; case, digits and punctuation are unchanged.
- Tick "Show all 25 shifts" if you do not know the key.
Why use this tool
Encrypts and decrypts with any shift from 1 to 25 and can show all 25 possible shifts at once, which is how you crack a Caesar message without the key. The Caesar cipher is the classic first cipher, used in puzzles, escape rooms, geocaching and classes on how encryption works. A tool avoids counting letters by hand and makes the brute-force attack, which is how the cipher is broken, a one-click task.
Why we built it
We built the Caesar cipher tool to show all 25 shifts at once, which is how a message is cracked without the key. Compare with ROT13 and the Morse code translator.
For a neighbouring job there is also the NATO Phonetic Alphabet Converter.
Who this tool is for
- Puzzle solvers and escape-room designers
- Students learning cryptography
- Teachers making a classroom activity
When to use it
- Solving a puzzle, geocache or escape-room clue.
- Teaching or learning basic cryptography.
- Checking a worked example.
- Making a simple coded message for a game.
How it works
Each letter is moved forward by the shift, modulo 26: with a shift of 3, X, Y and Z wrap to A, B and C. Decrypting moves each letter back by the same amount. A shift of 13 is ROT13, which is its own inverse.
Because there are only 25 useful shifts, the cipher is trivially broken: try them all and look for the one that reads as words. That is what the all-shifts table does. Julius Caesar is reported to have used a shift of 3 for military messages.
A Caesar cipher provides no real security. Use proper encryption for anything that matters.
What you give it, and what you get back
| Item | Details |
|---|---|
| Text | Any text; only the 26 letters A-Z are changed. |
| Direction and shift | Encrypt or decrypt, and a shift from 1 to 25. |
| Output | The shifted text, and optionally all 25 shifts in a table. |
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| The output is still unreadable | The shift or the direction is wrong. | Show all 25 shifts and look for the readable line. |
| Accented letters did not change | Only A-Z are shifted. | Remove or transliterate accents first. |
| Digits did not change | The Caesar cipher only rotates letters. | Use ROT13 with the digit option for numbers. |
Assumptions and limitations
- Letters A-Z only.
- A fixed shift for the whole message; no keyed or Vigenère variants.
- Not a secure cipher.
Frequently asked questions
What is a Caesar cipher?
A substitution cipher that replaces each letter with the one a fixed number of positions further down the alphabet.
How do I decode a Caesar cipher without the key?
Try every shift from 1 to 25 and pick the one that gives readable text. Tick "Show all 25 shifts" to see them together.
What shift did Julius Caesar use?
Accounts say he used a shift of 3.
Is a Caesar cipher secure?
No. With only 25 possible keys it is broken in seconds.
What is the difference between Caesar and ROT13?
ROT13 is a Caesar cipher with a shift of 13, so applying it twice gives the original.
Is my text or file sent anywhere?
No. Everything runs in your browser and nothing leaves the page.