The Caesar cipher is one of the oldest and simplest encryption techniques. It shifts every letter in the alphabet by a fixed number of positions. For example, with shift 3, A becomes D, B becomes E, and Z wraps around to C.
Encode shifts letters forward by the chosen amount to encrypt text. Decode shifts letters backward by the same amount to decrypt. Auto-decode tries all 26 possible shifts simultaneously and highlights rows that are likely readable English.
ROT13 is a Caesar cipher with a shift of 13. Because the alphabet has 26 letters, applying ROT13 twice returns the original text. It is widely used online to hide spoilers, puzzle answers, and mild profanity.
Auto-decode tries all 26 possible shifts and uses a vowel-ratio heuristic to detect which decoded outputs look like natural English. Rows that pass the check are highlighted so you can quickly find the correct shift.
No. Only letters A–Z (uppercase) and a–z (lowercase) are shifted. Spaces, numbers, punctuation, and all other characters remain unchanged in both encode and decode modes.
Any value from 0 to 25 works. Julius Caesar historically used shift 3. ROT13 (shift 13) is popular online. If you are decoding an unknown message, use Auto-decode mode to try all 26 shifts at once.