I created this tool to break the Substitution cipher used on https://www.improbableisland.com.
The goal is to keep the fun of cracking the cipher by hand while getting rid of the tedious task of constantly going over your text and replacing characters every time you found one.
This could be done on a piece of paper (or in a notepad) with a bit more time-investment.
This tool could also be used for educational stuff if you wanted to.
I even made a subdomain for it: https://paper.doesnotcut.it