Do I need separate encode and decode modes?

No. ROT13 is its own inverse, so applying it twice returns the original text. The same single operation both scrambles and unscrambles.

What happens to numbers and punctuation?

Only letters A–Z are rotated 13 places. Digits, spaces and punctuation are left exactly as they are.

Is anything sent to a server?

No. ROT13 runs entirely in your browser with JavaScript, so the text you enter never leaves your device.

No. ROT13 provides no security at all — anyone can decode it instantly. It is used to lightly obscure text, like spoilers, puzzle answers, or offensive jokes, so people only see it if they choose to decode it.

What is ROT13 commonly used for?

Hiding spoilers and punchlines in forums and Usenet, obfuscating email addresses against simple scrapers, and puzzle/CTF challenges. It is a convention for "hide this unless you want to read it", not encryption.

Is ROT13 the same as a Caesar cipher?

Yes — ROT13 is a Caesar cipher with a fixed shift of 13. The special property is that because 13 is half of 26, encoding and decoding are the same operation.

Does it keep uppercase and lowercase?

Yes. Case is preserved: uppercase letters rotate within A–Z and lowercase within a–z, so the capitalisation of your text is unchanged.

ROT13 Converter — Gera Tools

ROT13 (“rotate by 13”) is a simple letter-substitution cipher that replaces every letter with the one 13 places later in the alphabet. Because the alphabet has 26 letters, applying ROT13 twice returns the original text — so a single tool both encodes and decodes. It is widely used to hide spoilers and puzzle answers, not for real security.

How it works

For each letter, ROT13 shifts it 13 positions forward, wrapping around the end of the alphabet. Since 13 is exactly half of 26, shifting forward 13 and shifting back 13 land on the same letter — that is why the operation is its own inverse. The tool preserves case (uppercase stays uppercase, lowercase stays lowercase) and leaves digits, spaces, and punctuation untouched, rotating only the letters A–Z and a–z.

Example

Encoding Hello, World!:

Uryyb, Jbeyq!

Run that result through ROT13 again and you get Hello, World! back. Note the comma, space, and exclamation mark are unchanged.

Original	ROT13
A	N
N	A
Z	M
Gera Tools	Tren Gbbyf

Everything runs in your browser, so nothing you type is uploaded.