Hey there! 
How can I change players tablist header & footer using server side?

You can change player tablist header and footer by creating ClientboundTabListPacket and sending it to player.

Example:

public static ClientboundTabListPacket tabListPacket = new ClientboundTabListPacket(MutableComponent.create(new LiteralContents("Its header")), MutableComponent.create(new LiteralContents("Its footer")));

@SubscribeEvent
public static void onLoggedInEvent(PlayerEvent.PlayerLoggedInEvent loggedInEvent) {
	ServerPlayer serverPlayer = (ServerPlayer) loggedInEvent.getEntity();
	serverPlayer.connection.send(tabListPacket);
}

Edited November 15, 20231 yr by WeakInTheHead