ROT13 Encoder
Apply the classic ROT13 letter-substitution cipher.
ROT13 shifts every letter 13 places in the alphabet — a light, reversible way to hide spoilers, puzzle answers or jokes. Because the alphabet has 26 letters, applying ROT13 a second time returns the original text.
Formula / method
Examples
Uryyb
Hello
How ROT13 works
ROT13 replaces every letter with the one 13 places further along the 26-letter alphabet, wrapping around at the end: A becomes N, B becomes O, and so on. Because 13 is exactly half of 26, applying the shift a second time brings you right back to the original text, so a single function both scrambles and unscrambles. It is really a Caesar cipher locked to a shift of 13.
What it is (and is not) for
ROT13 is not encryption. It has no key and anyone can reverse it instantly, so it protects nothing sensitive. Its real historical use was on old Usenet forums to hide spoilers, joke punchlines, or puzzle answers so readers had to opt in to see them. Only the letters A-Z and a-z are rotated; digits, spaces, and punctuation pass through unchanged, which is why numbers in a ROT13 message stay perfectly readable.
Where it's used
- Hiding a spoiler, plot twist or puzzle answer in a forum post
- Obscuring a joke's punchline so readers choose when to reveal it
- Teaching how a Caesar or simple substitution cipher works
- Lightly masking text that should not be readable at a glance
- Quick reversible obfuscation where security is not the goal
Real-world examples
- 'Hello' becomes 'Uryyb', and applying ROT13 again turns 'Uryyb' back into 'Hello'
- Digits and punctuation pass through unchanged, so 'Level 42' becomes 'Yriry 42'
- 'The butler did it' is hidden as 'Gur ohgyre qvq vg'
A bit of history
ROT13 became popular on the Usenet newsgroup net.jokes in the early 1980s, with archived uses dating to 1982, as a courteous way to hide offensive jokes or spoilers so readers had to make a deliberate choice to decode them.
FAQ
Is ROT13 secure?
No. It is a simple substitution meant to obscure text, not protect it. Anyone can decode it instantly — applying ROT13 again reverses it.