Using / !isin $1 isn't going to do much, you want to check that he is not executing a command, you must:
-check that the first character is not a /, instead of checking that / is not in the string, sending "lol /" would fail, use $left($1,1)
-check that the first character is not the command character ($comchar), coupled with the first, it gives a nice $istok.
-check that control+enter hasn't been used with $ctrlenter, first to check that the command is going to be sent plain text but it is usually a good idea to prevent that kind of script to work when control is used anyway, to get a quick on/off
