diff --git a/build.gradle b/build.gradle
index 815e5fe..8faa09f 100644
--- a/build.gradle
+++ b/build.gradle
@@ -12,6 +12,7 @@ base {
 
 repositories {
     maven { url = "https://maven.fabricmc.net/" }
+    maven { url = "https://api.modrinth.com/maven" }
 }
 
 dependencies {
@@ -19,6 +20,9 @@ dependencies {
     mappings "net.fabricmc:yarn:1.21.1+build.3:v2"
     modImplementation "net.fabricmc:fabric-loader:0.16.5"
     modImplementation "net.fabricmc.fabric-api:fabric-api:0.116.12+1.21.1"
+
+    // Mod Menu — optional. Compile-only so the jar doesn't require it at runtime.
+    modCompileOnly "maven.modrinth:modmenu:11.0.3"
 }
 
 processResources {
diff --git a/gradle.properties b/gradle.properties
index e1dc041..099df92 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -8,4 +8,4 @@ archives_base_name=guiapi
 # Dependencies — keep in sync with build.gradle
 minecraft_version=1.21.1
 loader_version=0.16.5
-fabric_version=0.104.0+1.21.1
+fabric_version=0.116.12+1.21.1
diff --git a/src/main/java/dev/toolkitmc/guiapi/command/GuiCommand.java b/src/main/java/dev/toolkitmc/guiapi/command/GuiCommand.java
index 998386f..4086111 100644
--- a/src/main/java/dev/toolkitmc/guiapi/command/GuiCommand.java
+++ b/src/main/java/dev/toolkitmc/guiapi/command/GuiCommand.java
@@ -19,6 +19,8 @@
 /**
  * /guiapi open <namespace:id> [<targets>]
  * /guiapi list
+ * /guiapi reload
+ * /guiapi help
  *
  * Permission level 2 required.
  */
@@ -58,9 +60,17 @@ public static void register(CommandDispatcher<ServerCommandSource> dispatcher) {
 
                 .then(CommandManager.literal("list")
                     .executes(GuiCommand::listGuis))
+
+                .then(CommandManager.literal("reload")
+                    .executes(GuiCommand::reloadGuis))
+
+                .then(CommandManager.literal("help")
+                    .executes(GuiCommand::showHelp))
         );
     }
 
+    // ── Subcommand handlers ──────────────────────────────────────────────────
+
     private static int openGui(CommandContext<ServerCommandSource> ctx,
                                Collection<ServerPlayerEntity> targets) {
         Identifier id = IdentifierArgumentType.getIdentifier(ctx, "id");
@@ -90,8 +100,44 @@ private static int listGuis(CommandContext<ServerCommandSource> ctx) {
         StringBuilder sb = new StringBuilder("[GuiAPI] Loaded GUIs (" + all.size() + "):\n");
         all.forEach((id, def) ->
                 sb.append("  ").append(id)
-                  .append(" [pages=").append(def.getPageCount()).append("]\n"));
+                  .append(" [rows=").append(def.getRows())
+                  .append(", pages=").append(def.getPageCount()).append("]\n"));
         ctx.getSource().sendFeedback(() -> Text.literal(sb.toString().trim()), false);
         return all.size();
     }
+
+    private static int reloadGuis(CommandContext<ServerCommandSource> ctx) {
+        // Delegates to the server's full resource reload so GuiRegistry.apply()
+        // fires through the normal Fabric reload pipeline — same as /reload.
+        ctx.getSource().getServer()
+                .reloadResources(ctx.getSource().getServer().getDataPackManager().getEnabledIds())
+                .thenRun(() -> ctx.getSource().sendFeedback(
+                        () -> Text.literal("[GuiAPI] Reload complete. " +
+                                GuiRegistry.INSTANCE.getAll().size() + " GUI(s) loaded."),
+                        true))
+                .exceptionally(ex -> {
+                    ctx.getSource().sendError(
+                            Text.literal("[GuiAPI] Reload failed: " + ex.getMessage()));
+                    return null;
+                });
+        return 1;
+    }
+
+    private static int showHelp(CommandContext<ServerCommandSource> ctx) {
+        String help =
+                "[GuiAPI] Commands (permission level 2):\n" +
+                "  /guiapi open <id> [targets] - Open a GUI for yourself or target players\n" +
+                "  /guiapi list               - List all loaded GUI definitions\n" +
+                "  /guiapi reload             - Reload all datapack resources (including GUIs)\n" +
+                "  /guiapi help               - Show this help message\n" +
+                "\n" +
+                "Button JSON fields:\n" +
+                "  slot, page, item, name, lore, glint\n" +
+                "  click_type: any | left | right | shift  (default: any)\n" +
+                "  condition:  has_tag | score_gt | score_lt | score_eq\n" +
+                "  actions:    run_command | close | open_gui | message\n" +
+                "              next_page | prev_page | goto_page";
+        ctx.getSource().sendFeedback(() -> Text.literal(help), false);
+        return 1;
+    }
 }
diff --git a/src/main/java/dev/toolkitmc/guiapi/gui/BarrelGuiHandler.java b/src/main/java/dev/toolkitmc/guiapi/gui/BarrelGuiHandler.java
index 165460d..888d0b7 100644
--- a/src/main/java/dev/toolkitmc/guiapi/gui/BarrelGuiHandler.java
+++ b/src/main/java/dev/toolkitmc/guiapi/gui/BarrelGuiHandler.java
@@ -60,8 +60,10 @@ public static void open(ServerPlayerEntity player, GuiDefinition def, int page)
         int rows = Math.clamp(def.getRows(), 1, 6);
         int finalPage = page;
 
-        SimpleInventory inv = buildInventory(player, def, page, rows * 9);
+        // Register state BEFORE building inventory so that any handleClick call
+        // triggered during screen open (edge case) already sees the correct state.
         OPEN_GUIS.put(player.getUuid(), new OpenState(def, page));
+        SimpleInventory inv = buildInventory(player, def, page, rows * 9);
 
         String pageIndicator = def.getPageCount() > 1
                 ? " §8[" + (page + 1) + "/" + def.getPageCount() + "]"
@@ -82,17 +84,34 @@ public net.minecraft.screen.ScreenHandler createMenu(
     }
 
     public static boolean handleClick(ServerPlayerEntity player, GuiDefinition def,
-                                      int page, int slot, SlotActionType actionType) {
-        if (actionType != SlotActionType.PICKUP && actionType != SlotActionType.QUICK_MOVE)
-            return true; // consume but ignore
+                                      int page, int slot, int mouseButton, SlotActionType actionType) {
+        // Resolve what kind of click this actually is.
+        // mouseButton: 0 = left, 1 = right (Minecraft protocol)
+        // actionType QUICK_MOVE = shift+click
+        final boolean isShift = actionType == SlotActionType.QUICK_MOVE;
+        final boolean isLeft  = !isShift && mouseButton == 0 && actionType == SlotActionType.PICKUP;
+        final boolean isRight = !isShift && mouseButton == 1 && actionType == SlotActionType.PICKUP;
+
+        // Consume every action type to block item manipulation.
+        // Only PICKUP and QUICK_MOVE can actually trigger button actions.
+        if (!isLeft && !isRight && !isShift) return true;
 
         for (GuiDefinition.Button btn : def.getButtonsForPage(page)) {
             if (btn.slot() != slot) continue;
-            if (!evaluateCondition(player, btn)) continue; // invisible button, ignore
+            if (!evaluateCondition(player, btn)) continue;
+
+            // Check click_type filter
+            boolean matches = switch (btn.clickType()) {
+                case LEFT  -> isLeft;
+                case RIGHT -> isRight;
+                case SHIFT -> isShift;
+                case ANY   -> isLeft || isRight || isShift;
+            };
+            if (!matches) continue;
 
             for (GuiDefinition.ButtonAction action : btn.actions()) {
                 boolean shouldBreak = executeAction(player, def, page, action);
-                if (shouldBreak) break; // close/open_gui terminates chain
+                if (shouldBreak) break;
             }
             return true;
         }
@@ -122,7 +141,13 @@ private static SimpleInventory buildInventory(ServerPlayerEntity player,
 
     private static ItemStack buildStack(GuiDefinition.Button btn) {
         Identifier itemId = Identifier.tryParse(btn.item());
-        Item item = itemId != null ? Registries.ITEM.get(itemId) : Items.STONE;
+        Item item;
+        if (itemId != null && Registries.ITEM.containsId(itemId)) {
+            item = Registries.ITEM.get(itemId);
+        } else {
+            GuiApiMod.LOGGER.warn("[GuiAPI] Unknown item '{}' in slot {}, falling back to stone.", btn.item(), btn.slot());
+            item = Items.STONE;
+        }
 
         ItemStack stack = new ItemStack(item);
 
diff --git a/src/main/java/dev/toolkitmc/guiapi/gui/GuiDefinition.java b/src/main/java/dev/toolkitmc/guiapi/gui/GuiDefinition.java
index dd16b8a..84d1069 100644
--- a/src/main/java/dev/toolkitmc/guiapi/gui/GuiDefinition.java
+++ b/src/main/java/dev/toolkitmc/guiapi/gui/GuiDefinition.java
@@ -23,6 +23,7 @@
  *       "name": "§bClick Me",
  *       "lore": ["§7Line 1"],
  *       "glint": true,                    // enchantment glint effect
+ *       "click_type": "any",             // any (default) | left | right | shift
  *       "condition": {                    // optional visibility condition
  *         "type": "has_tag",             // has_tag | score_gt | score_lt | score_eq
  *         "value": "my_tag"             // tag name OR "objective:min:max" for score
@@ -58,6 +59,26 @@ public class GuiDefinition {
 
     // ── Enums ────────────────────────────────────────────────────────────────
 
+    /**
+     * Which mouse button triggers this button's actions.
+     *   ANY   — left or right click (default, original behaviour)
+     *   LEFT  — only left click
+     *   RIGHT — only right click
+     *   SHIFT — only shift+left click (QUICK_MOVE)
+     */
+    public enum ClickType {
+        ANY, LEFT, RIGHT, SHIFT;
+
+        public static ClickType fromString(String s) {
+            return switch (s.toLowerCase()) {
+                case "left"  -> LEFT;
+                case "right" -> RIGHT;
+                case "shift" -> SHIFT;
+                default      -> ANY;
+            };
+        }
+    }
+
     public enum ActionType {
         RUN_COMMAND, CLOSE, OPEN_GUI, MESSAGE, NEXT_PAGE, PREV_PAGE, GOTO_PAGE;
 
@@ -112,6 +133,7 @@ public record Button(
             String name,
             List<String> lore,
             boolean glint,
+            ClickType clickType,
             Optional<ButtonCondition> condition,
             List<ButtonAction> actions
     ) {}
@@ -157,6 +179,10 @@ private static Button parseButton(JsonObject b) {
         String name = b.has("name") ? b.get("name").getAsString() : "";
         boolean glint = b.has("glint") && b.get("glint").getAsBoolean();
 
+        ClickType clickType = b.has("click_type")
+                ? ClickType.fromString(b.get("click_type").getAsString())
+                : ClickType.ANY;
+
         List<String> lore = new ArrayList<>();
         if (b.has("lore") && b.get("lore").isJsonArray()) {
             for (JsonElement l : b.getAsJsonArray("lore"))
@@ -184,7 +210,7 @@ private static Button parseButton(JsonObject b) {
 
         if (actions.isEmpty()) actions.add(new ButtonAction(ActionType.CLOSE, ""));
 
-        return new Button(slot, page, item, name, lore, glint, condition, actions);
+        return new Button(slot, page, item, name, lore, glint, clickType, condition, actions);
     }
 
     private static ButtonAction parseAction(JsonObject a) {
@@ -201,7 +227,8 @@ private static ButtonAction parseAction(JsonObject a) {
 
     public Identifier getId()        { return id; }
     public String getTitle()         { return title; }
-    public int getRows()             { return rows; }
+    /** Always in [1, 6]. */
+    public int getRows()             { return Math.clamp(rows, 1, 6); }
     public int getPageCount()        { return pageCount; }
     public List<Button> getButtons() { return buttons; }
 
diff --git a/src/main/java/dev/toolkitmc/guiapi/gui/GuiScreenHandler.java b/src/main/java/dev/toolkitmc/guiapi/gui/GuiScreenHandler.java
index 7ce9ab9..905bf87 100644
--- a/src/main/java/dev/toolkitmc/guiapi/gui/GuiScreenHandler.java
+++ b/src/main/java/dev/toolkitmc/guiapi/gui/GuiScreenHandler.java
@@ -24,13 +24,16 @@ public GuiScreenHandler(ScreenHandlerType<?> type, int syncId,
 
     @Override
     public void onSlotClick(int slotIndex, int button, SlotActionType actionType, PlayerEntity player) {
-        if (slotIndex >= 0 && slotIndex < definition.getRows() * 9) {
+        // `getRows()` is from GenericContainerScreenHandler — always matches
+        // the actual inventory size, regardless of what GuiDefinition.getRows() returns.
+        int guiSlotCount = getRows() * 9;
+        if (slotIndex >= 0 && slotIndex < guiSlotCount) {
             if (player instanceof ServerPlayerEntity sp) {
-                BarrelGuiHandler.handleClick(sp, definition, page, slotIndex, actionType);
+                BarrelGuiHandler.handleClick(sp, definition, page, slotIndex, button, actionType);
             }
-            return; // consume, don't call super
+            return; // consume; don't call super
         }
-        // Block player inventory clicks too
+        // Block player-inventory clicks (slotIndex >= guiSlotCount) as well — no super call.
     }
 
     @Override
diff --git a/src/main/java/dev/toolkitmc/guiapi/loader/GuiRegistry.java b/src/main/java/dev/toolkitmc/guiapi/loader/GuiRegistry.java
index b3a26fd..5f177c9 100644
--- a/src/main/java/dev/toolkitmc/guiapi/loader/GuiRegistry.java
+++ b/src/main/java/dev/toolkitmc/guiapi/loader/GuiRegistry.java
@@ -53,6 +53,13 @@ protected Map<Identifier, GuiDefinition> prepare(ResourceManager manager, Profil
 
                        JsonObject json = GSON.fromJson(reader, JsonObject.class);
 
+                       // Reject unsupported GUI types explicitly (e.g. legacy "dialog" format)
+                       if (json.has("type") && !json.get("type").getAsString().equals("barrel")) {
+                           GuiApiMod.LOGGER.warn("[GuiAPI] Skipping {} — unsupported type '{}'. Only chest/barrel GUIs are supported.",
+                                   fileId, json.get("type").getAsString());
+                           return;
+                       }
+
                        // fileId looks like: <ns>:gui/<name>.json
                        // Compute logical GUI id: <ns>:<name>  (strip "gui/" prefix + ".json")
                        String path = fileId.getPath(); // "gui/my_gui.json"
diff --git a/src/main/java/dev/toolkitmc/guiapi/modmenu/GuiApiModMenuEntry.java b/src/main/java/dev/toolkitmc/guiapi/modmenu/GuiApiModMenuEntry.java
new file mode 100644
index 0000000..2dc3f8e
--- /dev/null
+++ b/src/main/java/dev/toolkitmc/guiapi/modmenu/GuiApiModMenuEntry.java
@@ -0,0 +1,89 @@
+package dev.toolkitmc.guiapi.modmenu;
+
+import com.terraformersmc.modmenu.api.ConfigScreenFactory;
+import com.terraformersmc.modmenu.api.ModMenuApi;
+import dev.toolkitmc.guiapi.loader.GuiRegistry;
+import net.minecraft.client.MinecraftClient;
+import net.minecraft.client.gui.screen.Screen;
+import net.minecraft.client.gui.screen.multiplayer.AddServerScreen;
+import net.minecraft.client.gui.widget.ButtonWidget;
+import net.minecraft.client.gui.widget.TextWidget;
+import net.minecraft.text.Text;
+
+/**
+ * Mod Menu integration — shows a simple info screen listing loaded GUIs.
+ *
+ * This class is only loaded when Mod Menu is present (modCompileOnly dependency).
+ * The entrypoint declaration in fabric.mod.json is under "modmenu", which Fabric
+ * Loader only invokes if the modmenu mod is installed.
+ */
+public class GuiApiModMenuEntry implements ModMenuApi {
+
+    @Override
+    public ConfigScreenFactory<?> getModConfigScreenFactory() {
+        return parent -> new GuiApiInfoScreen(parent);
+    }
+
+    // ── Simple info screen ───────────────────────────────────────────────────
+
+    private static class GuiApiInfoScreen extends Screen {
+
+        private final Screen parent;
+
+        protected GuiApiInfoScreen(Screen parent) {
+            super(Text.literal("GUI API"));
+            this.parent = parent;
+        }
+
+        @Override
+        protected void init() {
+            // Title
+            addDrawableChild(new TextWidget(
+                    width / 2 - 150, 20, 300, 10,
+                    Text.literal("§6GUI API §7— Datapack-driven chest GUI system"),
+                    textRenderer));
+
+            // Loaded GUI count
+            int count = GuiRegistry.INSTANCE.getAll().size();
+            addDrawableChild(new TextWidget(
+                    width / 2 - 150, 40, 300, 10,
+                    Text.literal("§7Loaded GUIs: §f" + count +
+                            (count == 0 ? " §c(join a world to load datapacks)" : "")),
+                    textRenderer));
+
+            // Loaded GUI list (up to 10)
+            int y = 60;
+            int shown = 0;
+            for (var entry : GuiRegistry.INSTANCE.getAll().entrySet()) {
+                if (shown >= 10) {
+                    addDrawableChild(new TextWidget(
+                            width / 2 - 150, y, 300, 10,
+                            Text.literal("§8... and " + (count - 10) + " more"),
+                            textRenderer));
+                    break;
+                }
+                var def = entry.getValue();
+                addDrawableChild(new TextWidget(
+                        width / 2 - 150, y, 300, 10,
+                        Text.literal("§a" + entry.getKey() +
+                                " §8[rows=" + def.getRows() +
+                                ", pages=" + def.getPageCount() + "]"),
+                        textRenderer));
+                y += 12;
+                shown++;
+            }
+
+            // Close button
+            addDrawableChild(ButtonWidget.builder(
+                    Text.literal("Close"),
+                    btn -> MinecraftClient.getInstance().setScreen(parent))
+                    .dimensions(width / 2 - 50, height - 30, 100, 20)
+                    .build());
+        }
+
+        @Override
+        public void close() {
+            MinecraftClient.getInstance().setScreen(parent);
+        }
+    }
+}
diff --git a/src/main/resources/fabric.mod.json b/src/main/resources/fabric.mod.json
index 911ac84..ffdf1db 100644
--- a/src/main/resources/fabric.mod.json
+++ b/src/main/resources/fabric.mod.json
@@ -20,6 +20,9 @@
   "entrypoints": {
     "main": [
       "dev.toolkitmc.guiapi.GuiApiMod"
+    ],
+    "modmenu": [
+      "dev.toolkitmc.guiapi.modmenu.GuiApiModMenuEntry"
     ]
   },
   "depends": {
@@ -27,5 +30,8 @@
     "fabric-api": "*",
     "minecraft": "~1.21.1",
     "java": ">=21"
+  },
+  "suggests": {
+    "modmenu": "*"
   }
-}
\ No newline at end of file
+}