ROT13 Decoder
Encode and decode ROT13 — the Caesar cipher with a fixed shift of 13. Because 13 is half of 26, ROT13 is its own inverse: the same button both hides and reveals text. Handy for spoilers and puzzle answers. Optionally add ROT5 for digits or switch to ROT47 for all printable ASCII. Everything runs in your browser; nothing is uploaded.
Runs entirely in your browser — nothing is uploaded. ROT13 is a readability trick for hiding spoilers, puzzle answers and the like, not encryption; it keeps nothing secret from anyone who runs it back through the same transform.
What this tool is
- A free, in-browser ROT13 tool: rotate every letter 13 places to hide or reveal text instantly.
- ROT13 is its own inverse — running text through it twice returns the original — so one button both encodes and decodes.
- Optional ROT5 rotates digits by 5 and ROT47 rotates all printable ASCII by 47, both also self-inverse.
- Everything runs client-side in JavaScript — nothing you type is ever sent to a server.
- ROT13 is a readability trick for hiding spoilers and puzzle answers, NOT encryption — it keeps nothing secret.
How ROT13 works
ROT13 stands for "rotate by 13 places". It is a Caesar shift of 13: each letter is replaced by the one 13 positions later in the alphabet, wrapping around at the end. So A↔N, B↔O, Hello becomes Uryyb. Digits, spaces and punctuation are untouched, and upper/lower case is preserved.
Its own inverse
Since 13 + 13 = 26 — a full trip around the 26-letter alphabet — applying ROT13 twice returns the original text. Encoding and decoding are therefore the exact same operation, which is why this tool has one button rather than separate modes. Paste cipher text or plaintext, and ROT13 gives you the other.
ROT5 and ROT47
- ROT5 rotates the digits 0–9 by five. Combined with ROT13 (sometimes called ROT13.5 or ROT18) it also scrambles numbers, and it too is its own inverse.
- ROT47 rotates all 94 printable ASCII characters (
!through~) by 47, so it also affects punctuation and symbols — again self-inverse.
Security note: ROT13 is not encryption. It has no key and anyone can reverse it in a second, so it is a readability convention for hiding spoilers and puzzle answers — never a way to keep information secret. For real confidentiality use a modern authenticated cipher such as AES-GCM.
Frequently asked questions
What is ROT13?
ROT13 ("rotate by 13 places") is a simple letter-substitution scheme that replaces each letter with the one 13 positions later in the alphabet: A becomes N, B becomes O, and so on, wrapping around so N becomes A again. It is a special case of the Caesar cipher with a fixed shift of 13. Non-letters — spaces, digits and punctuation — are left unchanged.
Why is ROT13 its own inverse?
The Latin alphabet has 26 letters, and 13 is exactly half of 26. Shifting a letter forward by 13 and then forward by 13 again moves it a full 26 places, which lands back on the original letter. So encoding and decoding are the identical operation — you run text through ROT13 to hide it and run the result through ROT13 again to reveal it. That is why this tool needs only one button instead of separate encode and decode modes.
What is ROT13 used for?
ROT13 is used to lightly obscure text that a reader should only see if they choose to — not to keep secrets. Common uses include hiding movie or book spoilers, puzzle and riddle answers, joke punchlines, and potentially offensive words in online forums and Usenet posts, so they are unreadable at a glance but trivially decoded on purpose. It is a readability convention, not a security measure.
Is ROT13 encryption? Is it secure?
No. ROT13 is not encryption and offers no security whatsoever. It has no key — anyone who knows it is ROT13 (or simply tries it) can read the text instantly, and even without that knowledge it falls to a trivial brute-force or frequency analysis like any Caesar cipher. It is sometimes jokingly cited as an example of "encryption" that provides zero protection. Never use ROT13 to protect anything sensitive; for real confidentiality use a modern authenticated cipher such as AES-GCM.