ROT13 Cipher

Encode or decode text with ROT13. Applying it twice restores the original.

Input

ROT13 Output

What Is ROT13?

ROT13 ("rotate by 13 places") is the simplest Caesar cipher variant — each letter shifts 13 positions through the alphabet. Because the English alphabet has exactly 26 letters, applying ROT13 twice always returns the original text, meaning encode and decode are the exact same operation. It was popularized in online forums and Usenet groups to hide spoilers, puzzle answers, and off-topic content from casual readers. ROT13 provides no real cryptographic security; it is purely a light obfuscation technique. Non-alphabetic characters — digits, punctuation, spaces — pass through unchanged. Everything runs entirely in your browser with no data sent to any server.

Built and maintained by Meet Shah · Last updated 19 July 2026

What this tool is used for

Concealing a spoiler or answer in plain text so that reading it requires a deliberate step.
Undoing text that was posted rotated, using the identical operation rather than a separate decode path.
Illustrating a fixed-shift substitution cipher where there is no key to manage at all.
Producing text that defeats a casual glance but no actual analysis whatsoever.
Testing whether a pipeline preserves letters and punctuation distinctly.

Frequently Asked Questions

Why is ROT13 its own inverse?: Because the alphabet has 26 letters and 13 is exactly half. Applying it twice rotates a full 26 and returns the original, so encoding and decoding are the same operation — which is why the tool needs no direction switch.
Is it encryption?: No, and it has never claimed to be — there is no key. It is a reversible obfuscation, roughly the digital equivalent of printing an answer upside down: enough to stop you reading something accidentally, no protection whatsoever against anyone who wants to.
What was it used for?: Usenet convention from the early 1980s: spoilers, punchlines and offensive jokes were posted rotated so a reader had to opt in. Newsreaders had a single key for it, which is how the convention survived long enough to become a joke in itself.
What happens to digits and punctuation?: They pass through untouched, along with spaces and every non-Latin character. Only A–Z and a–z rotate, and case is preserved — so the shape of the text stays recognisable, which is part of why it reads as obviously encoded.
What is ROT47?: The same idea across the 94 printable ASCII characters from `!` to `~`, so digits and punctuation rotate too. It is also self-inverse, being half of 94, and it garbles text far more thoroughly — while being exactly as insecure.
Why does it survive as a convention rather than a tool?: Because its weakness is the point. It marks text as "do not read yet" without pretending to secure it, so the reader chooses to decode. A real cipher would signal a secret worth attacking, which spoilers are not.

Common errors and gotchas

Using it where confidentiality matters. The shift is public and reversing it needs no key and no effort.
Expecting non-letters to move. Digits, spaces and punctuation pass through unchanged by definition.
Applying it twice and reporting that the output did not change, when returning to the original is the defining property.
Assuming it covers accented or non-Latin letters, which it leaves alone and can leave a message partly legible.
Confusing it with ROT47, which rotates a much larger printable range and behaves differently on punctuation.