ROT13 / Mật mã Caesar

A Caesar cipher cyclically shifts every letter of the alphabet by a fixed number of positions. ROT13 is the special case with a shift of 13, which makes the cipher self-inverting: apply ROT13 twice and you get the original text back.

How to use it

• For ROT13, just paste text — encoding and decoding are the exact same operation.
• For a custom Caesar shift, specify how many positions to shift (1-25).
• Digits, punctuation, and non-Latin characters are left unchanged.

Common uses

• Hiding a spoiler or answer in a forum post so it isn't read accidentally at a glance.
• A historical or teaching example of the simplest substitution cipher when learning cryptography.
• Light obfuscation of text in code or a config where cryptographic strength isn't needed.

Things to keep in mind

ROT13 is not encryption in any security sense — it's obfuscation, trivially broken by hand without any tool or key.

Since the Latin alphabet has 26 letters and 13 is exactly half of that, ROT13 is symmetric: the same operation encodes and decodes.