This a command line utility that helps you get useful information a selected window. I use this to get the WM_CLASS of certain windows that I want to have special rules in a tiling window manager (like i3 or dwm).

You need to run it in terminal:

$ xprop

And than click on a window with the cursor, then you will get the information you need in the terminal window.

This also runs from terminal, opening a white background window where you click or type and you get the output in the terminal window where you started xev.

$ xev

Useful to get keycode for any key on the keyboard, like the special media keys. But don't type or click a lot, because it will harder to identify the info.