Keyboard detector

Hi! I am trying to make a keyboard detector/guessing script, but i don't know exactly HOW to do it. I want to make a script that can automatically detect what the player is typing in the keyboard. I know that some people will suspect, but i don't want to use it in "the bad way". I just wanted to know how to make this because i wanted to use it "hereafter" in my game. I am planning to use this to identify and mute all the strong language in my chat (something like a filter) and in making some cheat codes.

I already did this when i was in the Robotics class, but it was long ago and it wasn't Javascript and C# so i don't know how to make this in these languages. I also searched a lot but i didn't find any answer. I have a script here that I THINK that guess it. It detecs if the player has pressed my custom word and then make somehting. If you guys want i can post it here.

Thank you =]