Caesar Cipher
Encrypt and decrypt text with a shift cipher.
How to use
- 1 Choose whether to encrypt or decrypt.
- 2 Set the shift amount (use 13 for classic ROT13).
- 3 Type or paste your text into the input box.
- 4 Read the transformed output and copy it.
About Caesar Cipher
The Caesar Cipher tool applies one of the oldest known encryption methods, named after Julius Caesar, who reportedly used it to protect military messages.
The idea is simple: every letter in your text is shifted a fixed number of places along the alphabet, so with a shift of three an A becomes a D, a B becomes an E, and so on, wrapping back to the start when it runs past Z.
Decrypting is just the same shift in the opposite direction.
This tool lets you pick any shift value, encrypt or decrypt at the flip of a dropdown, and watch the output update live as you type.
The letter case of your text is preserved, and anything that is not a letter — digits, spaces, punctuation, emoji — passes through untouched, so the structure of your message stays intact.
A shift of 13 gives you ROT13, the familiar self-reversing transformation used to hide spoilers and puzzle answers; running ROT13 twice returns the original text.
The Caesar cipher is a teaching and puzzle tool, not real security: with only 25 meaningful shifts it is trivially broken by trying them all.
It is perfect for classroom demonstrations, escape-room clues, light obfuscation and learning how substitution ciphers work.
Everything runs locally in your browser, so your text never leaves your device.
FAQ
Is the Caesar cipher secure?
No. With only 25 possible shifts it can be broken in seconds by trying them all. Use it for learning, puzzles and light obfuscation, never for real secrets.
What is ROT13?
ROT13 is a Caesar cipher with a shift of 13. Because the alphabet has 26 letters, applying it twice returns the original text, so the same operation both encodes and decodes.
Are numbers and punctuation changed?
No. Only the 26 letters A–Z are shifted. Digits, spaces, punctuation and other characters are left exactly as they are.