Dev Mode on, Dev Mode off. Dev Mode on, Dev Mode off...
Configurable on/off icons, alter the colors for the "in development mode" flaring on the left of the ACP, etc.
But wait! There is also constants toggling on/off while IN_DEV! The only hitch is you must FIRST add the constants you use/want/need in to the constants.php file manually. A safer, more clean, experience all-around - otherwise I would have to prep every constant available and most of them no-one ever uses. Again, this toggle power is only while you are in Dev Mode. This is a dev tool; not a live site one.
This was the first ACP flip-switch for dev mode. Prior to this plugin you would need to edit constants.php every time you wanted in or out of dev.
And yes, just like the old Marketplace listing said, I was way drunk when I wrote this. But that was the initial version. All of the subsequent releases I've been quite, quite sober.
Probably.