Nope, it sends stdout to sheets. Getting input from sheets would be cool, too.
tosheets --spreadsheet=ABC <myfile.txt
In this example, stdin is what goes to the spreadsheet. stdout is (I assume) nothing.Should you pipeline stdout from somewhere else to this utility, the contents of that stdout will be forwarded to Google Sheets.
It is correct to say either that you are forwarding stdin or that you are forwarding stdout. It is therefore not correct to say that it does not forward stdin, because the source code explicitly refers to stdin. That's likely the reason for the [Fight Club]s the GP is receiving.
Please don't comment about the voting on comments. It never does any good, and it makes boring reading.