While we encourage players to retain the Vanilla experience as much as possible, we understand that at times you may want a little help. When we are running Bukkit/Spigot, we also install some administrative mods to help us keep track of things on the server and minimize the amount of information we have to remember or pull up references for. So we get that there is occasionally a need to give yourself a little hand up with a client-side mod or two.
Our guidelines around this are simple. As long as it doesn’t impact your ability as a player or the world itself, then it is an allowable mod. Examples of a non-allowed mod would be those that make you fly, run at super speed, go invisible without potions, increase mining speed, gain access to ores or materials quicker, teleport, etc. Anything that gives you a distinct game advantage over other players, please clarify with an admin before use on the server.
Allowed mods are those that are undetectable by other players. Minimaps are a good example of this, as are resource packs (unless those packs give you a distinct advantage as mentioned above), and camera mods. Other mods that allow you to automate certain regular actions are also OK, such as Better Sprinting and Macro/Keybind. Resource management mods such as Not Enough Items and Inventory Tweaks are also allowed.
We ask that if you are going to use these mods, you do so in a manner that still adheres to the general rules. For example, don’t use Auto Click to go AFK at a spawner. While your player may not technically be AFK, you yourself are, and that can cause problems if something goes wrong and you are not there to address the issue when an admin is trying to figure it out.
Of course, some of these mods are not even updated yet for 1.13, so it may be hard for you to implement them in the current server, and there are no plans to roll back the server to accommodate out of date mods, so please do not ask.
If you have doubts as to whether the mod you are using is allowed, please contact an admin for further review and we will let you know.