Although it is possible to obtain the mode value in userland, it is quite cumbersome and possibly brittle (either parsing xdebug info, or checking XDEBUG_MODE and xdebug.mode ini settings then replicating xdebug's procedure for arriving at a value).

My personal use case is for my composer/xdebug-handler package, to not restart the process without xdebug if the mode is "off" - and for composer to not display a warning about xdebug being loaded in this situation. However I am sure that such a function would prove useful to others.

I have knocked up an example function and will PR it for your perusal.