Free ROT13 & Caesar Cipher Encoder/Decoder

ROT13 ("rotate by 13 places") is a special case of the Caesar cipher that shifts each letter by 13 positions in the alphabet. Since the alphabet has 26 letters, applying ROT13 twice returns the original text — the same function both encodes and decodes. It is commonly used to obscure spoilers, puzzle solutions, or sensitive text in online forums.

The Caesar cipher is one of the simplest and most widely known encryption techniques. Named after Julius Caesar, who used it for private correspondence, it works by shifting each letter in the plaintext by a fixed number of positions down the alphabet. For example, with a shift of 3, A becomes D, B becomes E, etc. Caesar ciphers have no security value by modern standards but remain excellent for learning cryptography fundamentals.

No. Both ROT13 and Caesar ciphers offer zero cryptographic security. With only 25 possible shifts (26 including ROT13), a brute-force attack takes seconds. They are useful only for obfuscating text (hiding spoilers, puzzle answers) or for educational purposes. Never use them to protect sensitive data.

Choose a mode: ROT13 applies a fixed 13-character rotation; Caesar Cipher lets you choose any shift (1-25) and direction (encode or decode). Type or paste text into the input panel, then click "Apply ROT13" or "Apply" to see the result. Use "Load Sample" to try a preset example, and click the copy icon or "Copy Result" to copy the output to your clipboard.

If the shift amount is unknown, try all 25 possible shifts manually by adjusting the slider. Look for the shift that produces readable English text. For automated analysis, you could use a frequency analysis tool — but trying all shifts manually with this tool only takes a few seconds since each shift previews instantly.