Caesar Cipher Encoder & Decoder

Enter a number between 1 and 25
Press Enter to encode, Shift+Enter for new line

Below is everything you need to **understand**, **use**, and **master** the Caesar Cipher — including examples, ROT13, a shift table, and some puzzles to test your skills. If you just want to convert text, the tool is available above. If you're here to learn, grab a coffee in fact forget that, grab a cup of tea (I am English afterall) and enjoy.

What Is the Caesar Cipher?

The Caesar Cipher is a type of substitution cipher where every letter in the alphabet is replaced by another letter that is a fixed number of positions away.

For example, using a shift of +3: 

Plaintext:  A B C D E F G
Ciphertext: D E F G H I J

So the word CAT becomes FDW. That's really all Julius Caesar did to protect his military messages — and he arguably conquered half the known world using this cipher.

How the Shift Works

Every shift wraps around the alphabet. So a shift of +1 turns Z into A. A shift of −1 turns A into Z. The encryption key is simply the number of positions you choose to rotate.

Here’s the full alphabet with a +3 shift:


A → D    G → J    M → P    S → V    Y → B
B → E    H → K    N → Q    T → W    Z → C
C → F    I → L    O → R    U → X
D → G    J → M    P → S    V → Y
E → H    K → N    Q → T    W → Z
F → I    L → O    R → U    X → A

Encrypting a Message

To encrypt using the Caesar Cipher, follow these steps:

  1. Choose a shift (e.g., 3)
  2. Shift every letter forward by that amount
  3. Leave numbers, punctuation, and spaces alone (unless you prefer otherwise)

Example with shift +2:


Plaintext:  SECRET MESSAGE
Ciphertext: UGETGV OGUUCIG

Decrypting a Message

Decrypting is just reversing the shift. If the encryption was +5, then the decryption is −5.

Example with shift −5:


Ciphertext: MJQQT BTWQI
Plaintext:  HELLO WORLD

ROT13 – The Special Case

ROT13 is simply Caesar with a fixed shift of 13. Because the alphabet has 26 letters, shifting twice returns the original message: 

ROT13(HELLO) → URYYB  
ROT13(URYYB) → HELLO

ROT13 is commonly used online for hiding spoilers, puzzles, or punchlines. Here’s a quick example: 


Plaintext:  SPOILERS AHEAD
ROT13:      FCVBYREF NURNQ

Why the Caesar Cipher Is Easy to Break

As charming as it is, the Caesar Cipher isn’t secure by modern standards. Here’s why:

  • There are only 25 possible shifts — trivial to brute-force.
  • Letter frequency patterns remain unchanged.
  • Short messages can often be solved by eye.

Still, it remains a brilliant teaching tool — and great for puzzles, treasure hunts, and escape rooms.

Caesar Cipher Examples

Example 1 – Shift +3


Plaintext:  MEET ME AT MIDNIGHT
Ciphertext: PHHW PH DW PLGQLJKW

Example 2 – Shift +7


Plaintext:  PUZZLES ARE FUN
Ciphertext: WBGGSLZ HYL MBU

Example 3 – Shift −4


Ciphertext: EVOO
Plaintext:  JAVA

Try Solving These Caesar Cipher Puzzles

Puzzle 1 – Easy

WKLV LV D VLPSOH RQH

Hint: Classic shift.

Puzzle 2 – Medium

GRRUV RSHQ ERQXV SOD\

Puzzle 3 – Harder

ZOPWWL TL HSZL

Hint: Negative shift this time.

Answers are intentionally not shown on-page (Google dislikes hidden text). But if you'd like, I can generate a separate link with the solutions.

History: Did Caesar Really Use It?

Yes — Julius Caesar used this exact method to communicate with his generals. He reportedly preferred a shift of +3. It wasn’t high-security, but given the average literacy rate at the time, it did the job.

Today, the Caesar Cipher survives not in warfare but in puzzles, geocaching, escape rooms, and code-breaking games. It's a perfect gateway into the world of cryptography.

Related Tools

Frequently Asked Questions

Is the Caesar Cipher secure?

No. It’s fun, educational, but extremely easy to break.

What shift did Caesar use?

Traditionally, he used a shift of +3.

What is the difference between Caesar and ROT13?

ROT13 is just a Caesar Cipher with a fixed shift of 13.

Can you brute-force a Caesar Cipher?

Yes — there are only 25 possible shifts.

What is it used for today?

While not secure for serious cryptographic purposes, the Caesar cipher is commonly used in:

  • Puzzle games and escape rooms
  • Educational demonstrations of cryptography concepts
  • ROT13 (a special case with shift of 13, popular on internet forums)
  • Geocaching and treasure hunts