Make sure length of character set is of even number and consisted of unique symbols.
Character set:
Text to be encoded/decoded:
It's not usual ROT-13. It seems it supports unicode too. Will work on it when has time.
Download Code:
QBasic - Code is as it is. You can help me make better code
Python 3 - Simplest code of all
C - Over complicated
C - Little less compilicated
Visual Basic - simple code and simple GUI (GITHUB)
Python 2.X - Blog post of initial code
More info
https://www.rot13.com/
https://en.wikipedia.org/wiki/ROT13
ROT-13 in BrainFuck (Esoteric Programming Language)