Windows equivalent to xev (X Event Viewer)

There's a utility in the windows SDK, called spy++ that can do this.

To log all keyboard messages make sure you enable all windows in the system checkbox, and filter for Keyboard message types.

I've used PassMark KeyboardTest before and it was just what I needed. It shows what keys are being pressed on the keyboard.

It's not exactly free, but there's a free 30-day trial download available. Of course, if you only need it once you can probably get away with the evaluation version.

My usual quick solution for this is keylook.exe<1>.

<1> ftp://ftp.charlespetzold.com/ProgWin95/CHAP05/

You can try keycode.info

It is the only online keyboard tester which I found that respects location of modifier keys, i.e. you can see the difference between left Alt and right Alt for example. However, it only shows last event, but has no logging area. Probably you can contribute to author's project.

The keyboard debugger at

https://codepen.io/QDeltaE/pen/PjXWZr

Tracks full keyboard state