Ammount of blocks you can be outside the Worldborder before taking damage.
%worldborder_warning_time%
Time from the Worldborder before seing visual effects
%worldborder_warning_distance%
Distance from the Worldborder before seing visual effects
Installation:
Download PlaceholderAPI and put it in your plugins folder
Start server
Put this expansion in plugins/PlaceholderAPI/expansions
Do /papi reload in console
Use one of the given placeholders above in a plugin that hooks in PlaceHolderAPI
Compatibility: Sertain plugins don't use %% they use {}, featherboard is an example for that.That doesn't mean the expansion won't work just use the {} instead of the %% and it should work fine!