Caesar Cipher / ROT13

Encode or decode text using the Caesar cipher (shift each letter by N positions in the alphabet). ROT13 is the default — a special case where shift=13, meaning the same operation encodes and decodes. Useful for hiding spoilers, light obfuscation, or teaching cryptography.

How to use the Caesar Cipher / ROT13

Type text, drag the shift slider, see encoded output. Decode reverses the shift. ROT13 (shift=13) is its own inverse — encoding ROT13 of ROT13 gets you back the original.

About the Caesar cipher

Named for Julius Caesar (who reportedly used shift=3 for military messages), the Caesar cipher is the simplest substitution cipher. It has no cryptographic security — only 25 possible shifts, brute-forceable instantly. ROT13 emerged in early Usenet as a way to hide spoilers or punchlines that readers would deliberately decode rather than have them stripped by the eye.

For actual security, use AES, RSA, or any modern algorithm. For light obfuscation (hiding a spoiler tag, hiding a sample answer in a quiz), Caesar/ROT13 is fine.

Frequently asked questions

What shift does ROT13 use?
ROT13 shifts every letter by 13. Because the alphabet has 26 letters, applying ROT13 twice returns the original, so one operation both encodes and decodes.

Is the Caesar cipher secure?
No. With only 25 possible shifts it is trivially broken and offers no real security. Use it for puzzles, hiding spoilers or teaching, never for protecting data.

Does it shift numbers and symbols?
The classic Caesar cipher shifts letters only and leaves digits, spaces and punctuation unchanged. To shift other characters, use the ROT47 variant.
Embed this tool on your site

Free to embed, no attribution required (but appreciated). Paste this where you want the tool to appear: