ROT13 Decoder & Encoder
beginnerCaesar cipher with fixed shift of 13 — encode and decode are identical
What is ROT13?
ROT13 ("rotate by 13 places") is a special case of the Caesar cipher with a fixed shift of 13. Because the English alphabet has 26 letters, applying ROT13 twice gives back the original text — ROT13 is its own inverse. This self-reciprocal property makes it convenient for simple obfuscation.
How ROT13 Works
Replace each letter with the letter 13 positions away in the alphabet: A↔N, B↔O, C↔P, and so on. Because encoding and decoding use the same operation, there's no distinction between encode and decode mode — the button does the same thing either way.
ROT13 in Pop Culture
ROT13 was used on Usenet newsgroups in the 1980s-90s to hide spoilers, offensive jokes, or puzzle answers. It's still used today in online communities for the same purpose. The /r/startrek subreddit uses it for spoiler tags.
How to Break ROT13
ROT13 provides no security — simply apply ROT13 again to get the original message. Since the shift is always 13, there's no key to discover.
Frequently Asked Questions
How do I decode ROT13?
Enter your ciphertext in the tool above, select "ROT13" from the dropdown, choose Decode mode, and click the button. Results appear instantly.
What is ROT13 used for?
ROT13 was used since 1980s for secret communication. While not secure by modern standards, it's widely used in puzzles, escape rooms, and educational contexts.
How secure is ROT13?
ROT13 is not secure by modern standards — it can be broken quickly with basic cryptanalysis or brute force. Use it for puzzles and learning, not sensitive data.
Who invented ROT13?
ROT13 was invented by Usenet community around 1980s.