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Caesar Cipher illustration

Caesar Cipher

100% Free

Encode and decode Caesar cipher with a custom shift. Includes a one-click ROT13 toggle and a live alphabet map.

Custom Shift 0–25
Live ROT13
Client-Side
No Sign Up
3
Cipher text

The Caesar cipher is for learning and fun — it offers no real security. Everything runs in your browser.

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  • Responsive design
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<iframe
  src="https://tools.town/embed/caesar-cipher/"
  width="100%"
  height="600"
  style="border:none; border-radius:12px;"
  loading="lazy"
  title="Caesar Cipher">
</iframe>

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How to Use

  1. 1 Choose Encrypt to scramble text, or Decrypt to unscramble it
  2. 2 Set the shift amount with the slider (0–25), or tap ROT13 for a shift of 13
  3. 3 Type or paste your message into the input box
  4. 4 Read the transformed text instantly in the output box
  5. 5 Use the alphabet map to see exactly how each letter is shifted, then Copy the result

Features

  • Encrypt and decrypt with any shift from 0 to 25
  • One-click ROT13 toggle — the classic shift-13 cipher that's its own inverse
  • Preserves capitalisation and leaves numbers, spaces, and punctuation untouched
  • Live alphabet map shows how every letter is transformed
  • Wraps cleanly around the alphabet (Z back to A)
  • Runs 100% in your browser — your message is never uploaded

Why it Matters

The Caesar cipher is the simplest substitution cipher and the first one most people meet, which makes it a perfect on-ramp to cryptography. It's ideal for teaching, puzzles, escape rooms, and light obfuscation like hiding spoilers. Seeing the letters shift in real time turns an abstract idea into something you can actually watch work.

★★★★★

Use Cases

Learn Cryptography

Demonstrate substitution ciphers and why simple shifts are easy to break

Puzzles & Escape Rooms

Create coded clues and let players crack them with the right shift

Hide Spoilers

ROT13 a spoiler so only readers who choose to decode it can see it

Private by Default

Encode and decode locally without sending text to any server

What this tool does

The Caesar Cipher tool encodes and decodes text using the classic shift cipher. Pick a shift from 0 to 25 (or tap ROT13 for the famous shift of 13), type your message, and watch it transform in real time. A live alphabet map shows exactly how each letter is moved.

Capitalisation is preserved, and anything that isn’t a letter — spaces, numbers, punctuation — passes straight through.

How the Caesar cipher works

Each letter is shifted a fixed number of positions along the alphabet, wrapping around the end. With a shift of 3, A → D and Z → C. Decrypting is just shifting the other way. Because there are only 25 possible shifts, the cipher is trivial to break — which is exactly why it’s such a good teaching tool.

Privacy

Everything runs in your browser via the pure caesarCipher function. Nothing you type is uploaded or stored — you can verify this in your browser’s Network tab.

Frequently Asked Questions

What is a Caesar cipher?
It's a substitution cipher that shifts every letter a fixed number of places along the alphabet, wrapping from Z back to A. With a shift of 3, A becomes D, B becomes E, and so on. It's named after Julius Caesar, who reportedly used it for private correspondence.
What is ROT13?
ROT13 is a Caesar cipher with a shift of 13. Because the alphabet has 26 letters, shifting by 13 twice returns the original text — so the same operation both encodes and decodes. It's commonly used online to hide spoilers and punchlines.
How do I decode a Caesar cipher if I don't know the shift?
There are only 25 possible shifts, so you can try them all and pick the line that reads as real text. Switch to Decrypt and step the slider through each value, or check our guide for the brute-force approach.
Does it keep my capital letters and punctuation?
Yes. Uppercase stays uppercase, lowercase stays lowercase, and anything that isn't a letter — spaces, digits, punctuation — passes through unchanged.
Is the Caesar cipher secure?
No. With only 25 possible keys it can be broken in seconds, even by hand. It's wonderful for learning and fun but should never be used to protect real secrets — use modern encryption for that.
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Want to go deeper?

Browse all guides →
The Caesar Cipher and ROT13, E
caesar cipher

The Caesar Cipher and ROT13, Explained

How the Caesar cipher shifts letters, why ROT13 is its own inverse, how to break it by hand, and why it's a great teaching tool but no real security.

23 Jun 2026

5 min read

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