ROT13 / Caesar Cipher
Classic substitution ciphers — ROT13 and Caesar with a custom shift.
ROT13
Shifts each letter by 13. Apply twice to get the original back.
Caesar Cipher
ROT13 vs Caesar cipher
Both are substitution ciphers that shift letters by a fixed amount. ROT13 shifts by exactly 13 positions, which makes it self-inverse — applying ROT13 twice returns the original text. It was popular on Usenet forums for hiding spoilers. Caesar cipher (named after Julius Caesar, who reportedly used it with shift 3) lets you choose any shift from 1–25. To decode, apply the reverse shift: if you encoded with shift 5, decode with shift 21 (26 − 5).
Frequently asked questions
Is ROT13 encryption?
ROT13 is not secure encryption — it provides no real confidentiality because anyone who knows (or guesses) the scheme can instantly decode it. It's used for light obfuscation of spoilers, puzzle answers, and offensive content warnings, not for protecting sensitive data.
What shift does Caesar cipher use?
Julius Caesar historically used a shift of 3 — A becomes D, B becomes E, and so on. The slider in this tool defaults to 3 to honour that convention, but you can set any value from 1 to 25.
Does the cipher preserve numbers and punctuation?
Yes. Only Latin letters (A–Z, a–z) are shifted. Numbers, spaces, and all punctuation pass through unchanged. Case is preserved — uppercase letters stay uppercase and lowercase stay lowercase.
