/wb - list available commands like below (show help).
/wb set <radius> - set world border, centered on you.
/wb [worldname] set <radius> <x> <z> - set world border, with the x and z coordinates of the center specified.
Permission: worldborder.set (both commands above)
/wb [worldname] radius <radius> - change border radius for this world. The world needs to have already had a border set, since the x and z values are not modified.
Permission: worldborder.radius
/wb [worldname] clear - remove border for this world.
/wb clear all - remove all borders for all worlds.
Permission: worldborder.clear (both commands above)
/wb list - show full border information for all worlds.
Permission: worldborder.list
/wb shape square - set the border shape to "square" (default).
/wb shape round - set the border shape to "round".
Permission: worldborder.shape (both commands above)
/wb knockback <distance> - how far to move the player back inside the border when they cross it.
Permission: worldborder.knockback
/wb [worldname] fill [freq] [pad] - generate all missing chunks for this world, out to the border. The freq value is the number of times per second it will try to check/generate a chunk (default 20). For a server with players on it, you should probably stick with the default or possibly even a lower value. If you just want it to finish as quickly as possible, try 1000 or so. The pad value is how much of a buffer to add beyond your borders (default 176, should keep any more chunks from being generated by players).
Permission: worldborder.fill
/wb wshape [worldname] <square|round> - Override the shape for this world only. The world needs to have already had a border set. The default shape used by other worlds (set via /wb shape) will not be changed by this.
Permission: worldborder.wshape
/wb getmsg - display the message shown to people who cross the border.
Permission: worldborder.getmsg
/wb setmsg <message> - change the border message.
Permission: worldborder.setmsg
/wb delay <amount> - the number of server ticks it will wait between border checks, the default is 4 ticks (~200ms); each server tick is roughly ~50ms.
Permission: worldborder.delay
/wb whoosh <on|off> - turn knockback "whoosh" effect on or off.
Permission: worldborder.whoosh
/wb reload - re-load data from config.yml. Normally should never be needed, but here just in case.
Permission: worldborder.reload
/wb debug <on|off> - turn console debug output on or off. Also should normally never be needed.
Permission: worldborder.debug