Press any key on your keyboard - it lights up blue while held and turns green once it has registered, so any key that never lights up is dead or stuck. Nothing you type is stored or sent anywhere.
0keys tested
0keys on layout
0held down right now
0most held at once
This page can only see keys the browser passes on. The Windows key may open the Start menu, and keys like Print Screen, Fn and media keys often aren't reported at all - that doesn't mean they're broken. Browser shortcuts (Ctrl/Cmd combos, F5, F11, F12) are left working.