ROT13 / Caesar Cipher
Encode or decode text with ROT13 or a custom Caesar cipher shift.
Last updated August 26, 2026
About this tool
ROT13 is a simple letter-substitution cipher that shifts each letter 13 places through the alphabet — famously used on old Usenet forums to hide spoilers or punchlines from casual view. Because the alphabet has 26 letters, applying the same 13-shift twice returns the original text, making ROT13 its own inverse. This tool supports ROT13 as well as any custom Caesar cipher shift from 1–25.
Frequently asked questions
Is ROT13 secure encryption?
No — ROT13 provides zero real security and is trivial to reverse by hand. It's meant only for obscuring text from casual/accidental reading, like hiding a spoiler, not for protecting sensitive information.
Why does applying ROT13 twice return the original text?
Because the alphabet has 26 letters and ROT13 shifts by exactly half of that (13), shifting twice completes a full 26-letter rotation back to the start.
What's the difference between ROT13 and a Caesar cipher?
ROT13 is just a Caesar cipher with a fixed shift of 13. This tool lets you set any shift amount from 1 to 25 for a general Caesar cipher.