ROT13
"Hello, World!" becomes "Uryyb, Jbeyq!", and ROT13 again turns it back.
Caesar Cipher and ROT13
Encode or decode text with a Caesar shift or ROT13, or try all 25 shifts.
Runs in your browser — nothing you enter is sent to a server.
How the Caesar Cipher and ROT13 works
A Caesar cipher replaces every letter with the letter a fixed number of places further along the alphabet, wrapping round from Z to A. Upper and lower case are kept; numbers, spaces and punctuation don't change. Choose Decode to shift back.
ROT13 is the shift of 13. Because the alphabet has 26 letters, applying ROT13 twice gives back the original, so the same setting encodes and decodes. If you don't know the shift, decode and open Try all 25: the readable line is the answer.
Formula
new position = (position + shift) mod 26
With A = 0 … Z = 25. Decoding subtracts the shift.
Examples
Caesar's own shift
With a shift of 3, "Hello, World!" becomes "Khoor, Zruog!", and xyz wraps round to abc.
Frequently asked questions
Is a Caesar cipher secure?
Not at all — there are only 25 possible keys, so anyone can try them all in seconds, as this tool does. Use it for puzzles, games and teaching. For real secrets, use the Text Encryption tool.
Where is ROT13 used?
To hide spoilers, puzzle answers and punchlines in forums and newsletters, so they aren't read by accident.
Are accented letters shifted?
No. Only the 26 letters A–Z are shifted; é, ñ and other characters stay as they are.
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