Information

Minecraft version: 1.17.1
Modloader: Fabric
Fabric loader version: latest
Environment: Multiplayer

Mod name: Tree Harvester (Fabric)
Mod version: latest

Question

is this a server side mode?

Yes you can use it server side only, though if you use the config option to break all leaves instantly you'll probably want it on the client to prevent the sound from going crazy.