diff --git a/src/tools/list.ts b/src/tools/list.ts
index eb26422..a8dcbe5 100644
--- a/src/tools/list.ts
+++ b/src/tools/list.ts
@@ -192,7 +192,7 @@ export async function listToolHandler(
     }
 
     // Process the response based on item type
-    const effective_item_type = input.item_type || (input.app ? "application_windows" : "running_applications");
+    const effective_item_type = (input.item_type && input.item_type.trim() !== "") ? input.item_type : (input.app ? "application_windows" : "running_applications");
 
     if (effective_item_type === "running_applications") {
       return handleApplicationsList(
@@ -387,7 +387,7 @@ async function handleServerStatus(
 
 export function buildSwiftCliArgs(input: ListToolInput): string[] {
   const args = ["list"];
-  const itemType = input.item_type || (input.app ? "application_windows" : "running_applications");
+  const itemType = (input.item_type && input.item_type.trim() !== "") ? input.item_type : (input.app ? "application_windows" : "running_applications");
 
   if (itemType === "running_applications") {
     args.push("apps");
diff --git a/tests/unit/tools/list.test.ts b/tests/unit/tools/list.test.ts
index 3dfadef..3fa1711 100644
--- a/tests/unit/tools/list.test.ts
+++ b/tests/unit/tools/list.test.ts
@@ -983,4 +983,40 @@ describe("List Tool", () => {
       expect(() => listToolSchema.parse(input)).toThrow();
     });
   });
+
+  describe("buildSwiftCliArgs empty string handling", () => {
+    it("should treat empty string item_type as undefined and default correctly", () => {
+      // Test case where item_type is empty string (should default to running_applications)
+      const inputWithEmptyString: ListToolInput = {
+        item_type: "",
+        include_window_details: [],
+      };
+      
+      const args = buildSwiftCliArgs(inputWithEmptyString);
+      expect(args).toEqual(["list", "apps"]);
+    });
+
+    it("should treat empty string item_type with app as application_windows", () => {
+      // Test case where item_type is empty string but app is provided
+      const inputWithEmptyStringAndApp: ListToolInput = {
+        item_type: "",
+        app: "Safari",
+        include_window_details: [],
+      };
+      
+      const args = buildSwiftCliArgs(inputWithEmptyStringAndApp);
+      expect(args).toEqual(["list", "windows", "--app", "Safari"]);
+    });
+
+    it("should treat whitespace-only item_type as undefined", () => {
+      // Test case where item_type is just whitespace
+      const inputWithWhitespace: ListToolInput = {
+        item_type: "   ",
+        include_window_details: [],
+      };
+      
+      const args = buildSwiftCliArgs(inputWithWhitespace);
+      expect(args).toEqual(["list", "apps"]);
+    });
+  });
 });