ROT13 Converter
Instantly encode and decode text with ROT13. Preserves case, passes through numbers and punctuation, and works in real time — all in your browser.
Input Text
ROT13 Output
What Is ROT13?
ROT13 (short for "rotate by 13 places") is a simple letter substitution cipher that replaces each letter with the letter 13 positions after it in the alphabet. Because the English alphabet has 26 letters, applying ROT13 twice brings you back to the original text — making it its own inverse. It grew popular on Usenet newsgroups in the 1980s and 90s as a lightweight way to hide spoilers, punchlines, and offensive content without any keys or passwords. ROT13 is a special case of the older Caesar cipher, which Julius Caesar used (with a shift of 3) for private correspondence. Unlike real encryption algorithms like AES, ROT13 provides no actual security — it is purely an obfuscation technique. You will still find it used today in forum spoiler tags, puzzle games, and light content filtering. For a deeper look at substitution ciphers in general, the Khan Academy cryptography course is a great starting point.
How to Use
Paste or type your text
Click into the Input panel on the left and paste or type any text you want to encode (or decode — it works both ways).
See the result instantly
The ROT13 output appears in the right panel in real time as you type. No button to click.
Copy or download the result
Use the Copy button to copy the result to your clipboard, or Download to save it as a .txt file.
Example
Here is a quick before-and-after to show exactly how ROT13 works. Every letter shifts by 13 — uppercase stays uppercase, lowercase stays lowercase, and everything else (spaces, numbers, punctuation) passes through unchanged.
ROT13 encoding of a sentence
Hello, World! The quick brown fox jumps over the lazy dog.→ ROT13
Uryyb, Jbeyq! Gur dhvpx oebja sbk whzcf bire gur ynml qbt.FAQ
Why does applying ROT13 twice return the original text?
Because 13 + 13 = 26, which is exactly the length of the English alphabet. Shifting a letter by 13 and then by another 13 wraps all the way around, landing back at where you started. This makes ROT13 a self-inverse function — the same operation both encodes and decodes.
Is ROT13 a form of encryption?
Not really. ROT13 provides no cryptographic security. Anyone who knows what ROT13 is (or who simply tries a few shifts) can decode it instantly. It is purely an obfuscation tool — useful for hiding spoilers or joke punchlines, not for protecting sensitive data. For real encryption, use a proper algorithm like AES.
Where did ROT13 originally come from?
ROT13 became widely used on Usenet in the early 1980s. Before dedicated spoiler tags existed, people used ROT13 to blur out the endings of movies, the answers to riddles, and offensive jokes so that readers could choose whether to decode them. It is a variant of the ancient Caesar cipher.
What happens to numbers, spaces, and punctuation?
They pass through completely unchanged. ROT13 only rotates the 26 letters of the English alphabet (A–Z and a–z). Numbers, spaces, commas, periods, and any other characters come out exactly as they went in.
Does ROT13 preserve uppercase and lowercase?
Yes. The tool respects case — uppercase A–Z rotate within their own range, and lowercase a–z rotate within theirs. So "Hello" becomes "Uryyb", not "uryyb" or "URYYB".
Can I use this tool for non-English text?
ROT13 only works on the standard 26-letter Latin alphabet. Characters from other scripts — accented letters, Cyrillic, Chinese, Arabic, etc. — are not rotated and will pass through unchanged. If you need a cipher for Unicode text, you would need a different approach.