ROT13 Cipher
Apply the ROT13 letter rotation to any text. Encoding and decoding are the same operation — run it twice to get the original back.
ROT13 replaces each letter with the one 13 places later in the alphabet (A→N, N→A). Because 13 is half of 26, the cipher is its own inverse. It's a classic for hiding spoilers and puzzle hints — and this page reminds you plainly that it is not real encryption.
A→N, B→O … N→A, O→B. Numbers, punctuation, spaces, and non-English letters pass through unchanged. Run the result through again to get the original back.
How to use this calculator
- Type or paste your text into the box.
- The ROT13 result appears instantly — no button needed.
- Copy it, or paste ROT13 text back in to decode it to the original.
Worked example
Hello, World! becomes Uryyb, Jbeyq! — verified by running the cipher. Feed Uryyb, Jbeyq! back in and you get Hello, World! again, because encoding and decoding are the same operation.
Frequently Asked Questions
What is ROT13?
Each letter is replaced by the one 13 positions later in the alphabet: A becomes N, B becomes O, and N wraps back to A. Because 13 is exactly half of 26, applying ROT13 twice returns the original text — encoding and decoding are literally the same operation.
Is ROT13 encryption?
No. It is a substitution cipher with a single fixed key that anyone — or this page — reverses instantly. It only hides text from casual glances: forum spoilers, puzzle hints, joke encryption. Never use it for anything confidential; for that you need real cryptography like AES or a proper library.
Why 13?
Thirteen is exactly half the alphabet, which makes the cipher its own inverse — convenient in the pre-computer era, when you didn't want to maintain separate encode and decode tables. Julius Caesar famously used a shift of 3; ROT13 is its symmetric cousin, popularized on Usenet.
What happens to numbers, punctuation, and accented letters?
They pass through unchanged, as do non-Latin scripts. Only the 26 ASCII letters A–Z and a–z are rotated. So 'Hello, World! 123' becomes 'Uryyb, Jbeyq! 123' — punctuation, spaces, and digits untouched.
Where is ROT13 actually used?
Classic Usenet and forum spoiler tags, puzzle hunts, geocaching hints, and joke encryption in chat. Programmers also meet it in CTF (capture-the-flag) challenges and coding-interview string-manipulation problems. Anywhere the goal is obscurity from casual reading rather than security.