Free Caesar Cipher (ROT13)
Encode and decode text with a shift cipher.
What is the Caesar Cipher (ROT13)?
The Caesar cipher is one of the oldest encryption methods, named for Julius Caesar, who used it to shift each letter a fixed number of places down the alphabet. It's simple enough to do in your head — and simple enough to break just as easily — which makes it a perfect way to learn how ciphers work.
This tool encodes and decodes text with any shift, including the well-known ROT13, right in your browser.
Last updated: Aug 12, 2026
What does this tool do?
You enter text and a shift amount, and the tool moves each letter that many places through the alphabet, wrapping around from Z back to A.
It shows both the encoded and decoded results at once, and includes a one-click ROT13 (a shift of 13, which is its own inverse).
Key features
Any shift
Encode or decode with any offset.
ROT13 preset
The classic self-reversing shift.
Encode and decode together
See both results at once.
Preserves other characters
Numbers, spaces and punctuation pass through.
Private
Everything runs in your browser.
Example
Common use cases
- Students — Learn how substitution ciphers work.
- Teachers — Demonstrate basic cryptography.
- Puzzle makers — Create coded clues and riddles.
- Escape-room designers — Build cipher puzzles.
- Gamers — Decode ROT13 hints and spoilers.
- Kids and hobbyists — Send secret messages for fun.
- CS learners — Explore the basics of encryption.
- Forum users — Hide spoilers with ROT13.
Benefits
- It makes a classic cipher hands-on.
- ROT13 is one click for spoilers and puzzles.
- It shows both directions at once.
- Your text never leaves the browser.
Tips
- ROT13 applied twice returns the original text.
- A shift of 26 (or 0) leaves text unchanged.
- Only letters shift; numbers and symbols stay put.
- To crack a Caesar cipher, try all 25 shifts — it's quick.
- Case is preserved, so capitals stay capitals.
- It's for fun and learning, not real security.
- Combine with the binary or Morse tools for layered puzzles.
- Negative shifts decode a positive-shifted message.
Common mistakes to avoid
Relying on it for security
Fix: A Caesar cipher is trivially broken — never use it to protect real secrets.
Expecting numbers to shift
Fix: Only letters are shifted; digits and punctuation pass through unchanged.
Forgetting ROT13 is self-inverse
Fix: Applying ROT13 again decodes it — no separate decode needed.
Using the wrong shift to decode
Fix: Decode with the same shift used to encode (or its negative).
How it works
- 1
Enter text
Type or paste your message.
- 2
Set the shift
Choose a shift or use ROT13.
- 3
Copy
Copy the encoded or decoded text.
Frequently asked questions
A Caesar cipher with a shift of 13, where applying it twice returns the original text.
No. A shift cipher is trivially broken — it's for learning and fun, not real security.
A Caesar cipher with a shift of 13, where applying it twice returns the original text.
No. A shift cipher is trivially broken — it's for learning and fun, not real security.
No. Only letters are shifted; everything else passes through unchanged.
Use the same shift that encoded it, or a negative shift. ROT13 decodes itself.
Try all 25 possible shifts — with only 25 options it's very quick.
No. Everything runs in your browser.
Conclusion
The Caesar cipher is the friendliest way into cryptography, and ROT13 is genuinely handy for spoilers. Pair it with the binary and Morse tools for more encoding fun.
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