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Encoding & Decoding

ROT13 / Caesar Cipher

Encode and decode ROT13 text instantly, or use a configurable Caesar cipher with any shift 1-25.

ROT13 / Caesar Cipher
Client-side

About this tool

ROT13 is a simple letter-substitution cipher that rotates each alphabetic character 13 positions through the alphabet, wrapping from Z back to A. Because the alphabet has 26 letters, applying ROT13 twice returns the original text — encoding and decoding are literally the same operation, which is why ROT13 is popular for obscuring spoilers, puzzle answers, and forum content that shouldn't be readable at a glance.

This tool provides a one-click ROT13 mode with no encode/decode distinction needed since the operation is self-inverse. It also includes a general Caesar cipher mode with an adjustable shift from 1 to 25, showing both the encoded and decoded result side by side.

The underlying algorithm only rotates A-Z and a-z characters, preserving case, and leaves every other character — digits, punctuation, spaces, and non-Latin scripts — completely untouched.

Important: ROT13 and Caesar ciphers provide zero real security. They are trivially broken by frequency analysis or trying all 26 shifts, and are intended for lightweight obfuscation or education, never for protecting sensitive data.

FAQ

Why is ROT13 encode and decode the same button?
ROT13 shifts each letter 13 positions, and the alphabet has 26 letters — shifting forward 13 twice returns every letter to its original position, making ROT13 mathematically self-inverse.
Is ROT13 or Caesar cipher secure?
No. Both are trivially breakable by trying all 25 possible shifts. They provide obscurity for spoilers or puzzles, not real security. Use AES for anything that needs actual confidentiality.
What happens to numbers, punctuation, and spaces?
They are left completely unchanged. Only A-Z and a-z are rotated; case is preserved.
What is the difference between ROT13 and the general Caesar cipher mode?
ROT13 is a Caesar cipher with a fixed shift of exactly 13. The general mode lets you pick any shift from 1 to 25.
How do I decode Caesar cipher text if I don't know the shift?
Since there are only 25 possible shifts, try each value in the slider and see which produces readable text.