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.

ROT13 Converter

Encode and decode ROT13 — the letter-rotating cipher.

ROT13 converter

ROT13 (“rotate by 13”) replaces every letter with the one 13 places later in the alphabet. Because the alphabet has 26 letters, applying ROT13 twice gives you the original text back — so a single converter both encodes and decodes.

Digits, spaces and punctuation are untouched. Everything runs in your browser, so nothing you type is uploaded.