Free Tool
ROT13 Encoder / Decoder
ROT13 shifts every letter 13 places through the alphabet: A becomes N, N becomes A. It is the same operation to encode and to decode, which is why it is used to hide spoilers and puzzle answers — and why it must never be used to hide anything that matters. Try it below.
ROT13 is not encryption. Anyone can reverse it in one click — including with this very tool. It hides text from a casual glance, not from a reader. Never use it for anything secret.
What this tool does
ROT13 is the simplest cipher in common use. Each letter is replaced by the letter 13 places later in the alphabet, wrapping around at Z, so A becomes N and N becomes A. Because 13 is exactly half of 26, the operation is its own inverse: encoding a message twice gives you the original back, and the same button both encodes and decodes. Numbers, punctuation and spaces are left untouched.
ROT13 survives because it is useful for hiding text from a casual glance — a spoiler in a forum post, the answer to a puzzle, an offensive word in a quote — without pretending to be secure. Nobody who sees ROT13 thinks it is a secret; the point is that the reader must choose to decode it. That social contract is the whole use case, and it is the only one: ROT13 has no key, no secret, and no security at all, and anyone who knows the trick — which is everyone with a search engine — can read it instantly.
This page is the companion to the Caesar cipher simulator on this site. ROT13 is a Caesar cipher with a fixed shift of 13, so everything the Caesar page teaches about key spaces and breaking applies here in the extreme: the key space is one, and the cipher is broken by definition. Use this tool to encode a spoiler, to decode one, or to teach a beginner what a cipher is — and then move on to the encryption guides for the real thing.
Try it
Type text and ROT13 it. Press the button again on the result and you get the original back.
Waiting. Press ROT13 it. The same button encodes and decodes.
How it works
ROT13 is a Caesar cipher with a shift of 13. Each letter moves 13 places forward: A to N, B to O, M to Z, N back to A, and so on. Upper-case and lower-case letters are shifted separately, so the case is preserved, and anything that is not a letter is left as it is. Because the alphabet has 26 letters and 13 is half of that, shifting twice returns to the start: ROT13 of ROT13 is the original text. That is why the same function encodes and decodes, and why there is no key to share or to lose.
The operation is so simple that it can be done by hand, and so weak that it was never intended as security. It appears in internet culture as a way of hiding spoilers — the reader must deliberately decode the text, so they cannot be spoiled by accident — and in puzzles, where it is a first step rather than a solution. It also appears in old jokes and in some email headers, always as a fig leaf rather than a lock.
From a cryptography point of view, ROT13 has a key space of one. There is nothing to guess, nothing to brute-force, and nothing to keep secret. The Caesar cipher simulator on this site shows the same idea with a variable shift and 25 possible keys; ROT13 fixes the shift and reduces the keys to one. That is the difference between a toy cipher and a joke cipher, and it is why this page is labelled an encoder for fun and teaching, not a security tool.
Limitations
ROT13 provides no confidentiality at all. Anyone who recognises it — and the pattern is famous — can decode it in one click, including with this page. It must never be used to protect a password, a message, or any information that matters. It hides text from a glance, not from a reader.
- The tool shifts letters only. Numbers, punctuation, spaces and non-English letters pass through unchanged.
- There is no key and no security. Do not confuse ROT13 with encryption: encryption needs a key, and ROT13 has none.
- Nothing you type is sent anywhere. The computation is local, and the page works offline once loaded.
Examples
Example 1 — Hello, world. ROT13 of Hello, world is Uryyb, jbeyq. ROT13 of Uryyb, jbeyq is Hello, world again. The same button does both, because the operation is its own inverse.
Example 2 — hiding a spoiler. A forum post reads: Gur xvyyre vf gur ohgyre. Only a reader who deliberately decodes it learns the spoiler — The killer is the butler — and a reader scrolling past is not spoiled by accident. That social contract, not security, is the point of ROT13.
Example 3 — the Caesar connection. Set the Caesar cipher simulator on this site to a shift of 13 and you have ROT13. Set it to any other shift and you have a Caesar cipher with a key. The difference between them is the size of the key space — 25 for Caesar, one for ROT13 — and both are toys next to a modern cipher with billions of billions of keys.
Frequently asked questions
What is ROT13?
A cipher that shifts each letter 13 places through the alphabet. Because 13 is half of 26, the same operation both encodes and decodes — ROT13 of ROT13 is the original text.
Is ROT13 encryption?
No. It has no key and no security. Anyone can reverse it in one click. It hides text from a casual glance, not from a reader, and must never be used for anything secret.
Why is ROT13 used at all?
To hide spoilers, puzzle answers and mildly offensive text from accidental reading. The reader must choose to decode it, so nobody is spoiled by scrolling past.
How is ROT13 related to the Caesar cipher?
ROT13 is a Caesar cipher with a fixed shift of 13. The Caesar cipher lets you choose the shift; ROT13 fixes it at 13, which is half the alphabet — so encoding twice returns the original.
Can ROT13 hide a password?
No. Anyone who recognises ROT13 can decode it instantly. Never encode a password, a secret or a sensitive message in ROT13 and treat it as protected.