How did the WallstreetBet community know that Game Stop was shorted so heavily?

What I understand from the whole Game Stop soaring stock prices event is that Game Stop stocks were in essence shorted too heavily, there were more stocks borrowed/shorted than in existence. This enabled people from the WallstreetBet community and others to inflate the stock price massively by buying it. What I want to know is how/where the WallstreetBet community got the information that it was shorted so/too heavily. Were it just statements from big investors that they shorted heavily on Game Stop stocks? Or did/could they get information from other sources too about how much the stock was shorted?