Caesar Cipher and ROT13 Encoder/Decoder

Shift every letter in your text by a chosen amount to encrypt or decrypt it, or apply ROT13 — the classic fixed 13-position shift used across forums and Usenet to hide spoilers and puzzle answers.

Features:

• Any shift 1-25: Encrypt or decrypt with a custom amount.
• One-click ROT13: The most common fixed-shift variant.
• Brute-force viewer: Lists what every one of the 25 shifts would produce.

1. How a Caesar Cipher Works

Every letter is replaced by the letter a fixed number of positions later in the alphabet, wrapping back to "A" after "Z". A shift of 3 turns "A" into "D"; decrypting just shifts the same amount in the opposite direction. Numbers, spaces, and punctuation are left untouched.

2. Why ROT13 Is Special

Because the alphabet has 26 letters, shifting by exactly half (13) makes the cipher its own inverse — applying ROT13 twice returns the original text. That made it a convenient, low-friction way to obscure spoilers in plain text systems, not a way to actually keep anything secret.

3. Cracking an Unknown Shift

Since there are only 25 possible shifts, a Caesar cipher can always be broken by simply trying every one of them and reading off which result makes sense — exactly what the "Show all 25 shifts" button does automatically.