Obkey

https://github.com/nsf/obkey
Clone, cd to it, run ./obkey (and backup rc.xml before that).

https://wiki.archlinux.org/index.php/Openbox#rc.xml

The obkeyAUR utility provides a graphical interface for configuring key bindings. Before using obkey, you should use obconf to create ~/.config/openbox/rc.xml.