ROT13 & Caesar Cipher
Encode and decode text using ROT13 or a custom Caesar Cipher shift. ROT13 applies a fixed shift of 13, while the Caesar Cipher lets you choose any shift from 1 to 25. All processing happens locally in your browser.
ROT13 Encoder / Decoder
ROT13 shifts each letter by 13 positions. Since the alphabet has 26 letters, encoding and decoding are the same operation.
Caesar Cipher
Shift each letter by a custom amount. Use the slider or number input to set the shift value (1-25). The output updates live as you type or adjust the shift.
How It Works
The Caesar Cipher is one of the oldest known encryption techniques. Each letter in the plaintext is replaced by a letter a fixed number of positions further down the alphabet. For example, with a shift of 3: A becomes D, B becomes E, and so on. Letters wrap around, so X becomes A, Y becomes B, and Z becomes C.
ROT13 is a special case of the Caesar Cipher with a shift of 13. Because 13 is exactly half of 26 (the number of letters in the English alphabet), applying ROT13 twice returns the original text. This makes it self-reciprocal — the same operation encodes and decodes.
Only alphabetic characters (A-Z, a-z) are shifted. Numbers, punctuation, spaces, and other characters pass through unchanged. Letter case is preserved during the transformation.
Frequently Asked Questions
What is ROT13?
ROT13 is a simple letter substitution cipher that replaces each letter with the letter 13 positions after it in the alphabet. Because the alphabet has 26 letters, applying ROT13 twice returns the original text, making it its own inverse.
What is a Caesar Cipher?
A Caesar Cipher is a substitution cipher where each letter in the plaintext is shifted a fixed number of positions down the alphabet. It is named after Julius Caesar, who reportedly used it with a shift of 3 to communicate with his generals.
How do I decode a Caesar Cipher without knowing the shift?
Since there are only 25 possible shifts, you can try each one (brute force) and look for the output that produces readable text. Frequency analysis of the ciphertext can also help determine the shift value.
Is ROT13 secure for encryption?
No. ROT13 and Caesar Ciphers provide no real security. They are trivially broken and should only be used for obfuscation, puzzles, or hiding spoilers — never for protecting sensitive data.