From the server rules:
1.3 - The following modifications are ALLOWED and are the only the official version of the specified modifications can be used:
Optifine by sp614x or any similar client performance improvement modifications.
Modifications which allow the enhancement of shaders, graphics, etc. but do not provide a benefit such as ESP.
Modifications which display status messages of armour, active potions, etc.
Modifications which display a mini-map but do not show other player location data, entity values, etc.
You can find the rest of the rules here. However I'd suggest further clarifying with a staff member to be safe