the one change i wanted to make

src/main/java/noppes/npcs/CustomNpcs.java

@@ -64,6 +64,7 @@ import nikedemos.markovnames.generators.MarkovSlavic;
 import nikedemos.markovnames.generators.MarkovSpanish;
 import nikedemos.markovnames.generators.MarkovWelsh;
 import noppes.npcs.compat.PixelmonHelper;
+import noppes.npcs.config.ConfigClient;
 import noppes.npcs.config.ConfigMain;
 import noppes.npcs.config.LoadConfiguration;
 import noppes.npcs.config.legacy.LegacyConfig;
@@ -119,6 +120,9 @@ import noppes.npcs.entity.old.EntityNpcNagaMale;
 import noppes.npcs.entity.old.EntityNpcSkeleton;
 import noppes.npcs.scripted.NpcAPI;
 import somehussar.janino.AdvancedClassFilter;
+import tconstruct.client.tabs.InventoryTabCustomNpc;
+import tconstruct.client.tabs.InventoryTabVanilla;
+import tconstruct.client.tabs.TabRegistry;
 
 import java.io.File;
 import java.util.HashSet;
@@ -340,6 +344,15 @@ public class CustomNpcs {
 
     @EventHandler
     public void loadComplete(FMLLoadCompleteEvent ev) {
+        if (ev.getSide().isClient()) {
+            if (ConfigClient.InventoryGuiEnabled) {
+                MinecraftForge.EVENT_BUS.register(new TabRegistry());
+                if (TabRegistry.getTabList().isEmpty()) {
+                    TabRegistry.registerTab(new InventoryTabVanilla());
+                }
+                TabRegistry.registerTab(new InventoryTabCustomNpc());
+            }
+        }
         proxy.buildPackageIndex();
 
         // Load built-in animations on the client so they're available for ability preview.

src/main/java/noppes/npcs/client/ClientProxy.java

@@ -384,14 +384,6 @@ public class ClientProxy extends CommonProxy {
 
         // Lightning effect rendering system
         MinecraftForge.EVENT_BUS.register(new LightningHandler());
-
-        if (ConfigClient.InventoryGuiEnabled) {
-            MinecraftForge.EVENT_BUS.register(new TabRegistry());
-            if (TabRegistry.getTabList().isEmpty()) {
-                TabRegistry.registerTab(new InventoryTabVanilla());
-            }
-            TabRegistry.registerTab(new InventoryTabCustomNpc());
-        }
     }
 
     public FakePlayer getCommandPlayer(IWorld world) {