An extremely simple, and hopefully useful plugin. It's designed simplicity and compatibility across versions in mind, so should not need updating frequently. Players with a certain permission node will get a certain multiplier bonus on any XP they pick up while on your server. This plugin has 0 configuration files, 0 commands, just a grand total of 9 permission nodes to choose from.
Any players carrying one of these permissions will have any XP they pick up multiplied by the numbered permission. So, if a player picks up 10 xp with xpmultiplier.2, they will recieve 20 xp. If they have xpmultiplier.4, they would get 40 xp, and so on.
xpmultiplier.2 xpmultiplier.3 xpmultiplier.4 xpmultiplier.5 xpmultiplier.6 xpmultiplier.7 xpmultiplier.8 xpmultiplier.9 xpmultiplier.10
As you can see, these are the permission nodes. You don't need a multiplier of 1, since this is what you get anyway, and if a player inherits two of the permissions the higher one will always be set. You cannot multiply two permissions together or anything, that would get complicated and messy.
Personally I recommend not really going above 3x-4x for normal players, for the sake of balancing the game. Players can get a ton of xp from mob grinders already.
This plugin was not made by me, but for me. I paid for this, and am letting the public make use of it. Therefore, treat it 'as is' without ANY support given should it not work.