diff --git a/tests/test_todo_tool.py b/tests/test_todo_tool.py
index a193e8ee..5fa2b242 100644
--- a/tests/test_todo_tool.py
+++ b/tests/test_todo_tool.py
@@ -29,15 +29,15 @@ class FakeCollection:
         pass
 
     def insert_one(self, doc):
-        key = (doc["user_id"], doc["tool_id"], int(doc["todo_id"]))
+        key = (doc["user_id"], doc["tool_id"], doc["todo_id"])
         self.docs[key] = doc
         return type("res", (), {"inserted_id": key})
 
     def find_one(self, query):
-        key = (query.get("user_id"), query.get("tool_id"), int(query.get("todo_id")))
+        key = (query.get("user_id"), query.get("tool_id"), query.get("todo_id"))
         return self.docs.get(key)
 
-    def find(self, query):
+    def find(self, query, projection=None):
         user_id = query.get("user_id")
         tool_id = query.get("tool_id")
         filtered = [
@@ -47,7 +47,7 @@ class FakeCollection:
         return FakeCursor(filtered)
 
     def update_one(self, query, update, upsert=False):
-        key = (query.get("user_id"), query.get("tool_id"), int(query.get("todo_id")))
+        key = (query.get("user_id"), query.get("tool_id"), query.get("todo_id"))
         if key in self.docs:
             self.docs[key].update(update.get("$set", {}))
             return type("res", (), {"matched_count": 1})
@@ -59,7 +59,7 @@ class FakeCollection:
             return type("res", (), {"matched_count": 0})
 
     def delete_one(self, query):
-        key = (query.get("user_id"), query.get("tool_id"), int(query.get("todo_id")))
+        key = (query.get("user_id"), query.get("tool_id"), query.get("todo_id"))
         if key in self.docs:
             del self.docs[key]
             return type("res", (), {"deleted_count": 1})
@@ -69,6 +69,10 @@ class FakeCollection:
 @pytest.fixture
 def todo_tool(monkeypatch) -> TodoListTool:
     """Provides a TodoListTool with a fake MongoDB backend."""
+    # Reset the MongoDB client cache to ensure our mock is used
+    from application.core.mongo_db import MongoDB
+    MongoDB._client = None
+
     fake_collection = FakeCollection()
     fake_client = {settings.MONGO_DB_NAME: {"todos": fake_collection}}
     monkeypatch.setattr("application.core.mongo_db.MongoDB.get_client", lambda: fake_client)
@@ -76,52 +80,72 @@ def todo_tool(monkeypatch) -> TodoListTool:
 
 
 def test_create_and_get(todo_tool: TodoListTool):
-    res = todo_tool.execute_action("todo_create", title="Write tests", description="Write pytest cases")
-    assert res["status_code"] == 201
-    todo_id = res["todo_id"]
+    res = todo_tool.execute_action("create", title="Write tests")
+    assert "Todo created with ID" in res
+    # Extract todo_id from response like "Todo created with ID test_user_test_tool_1: Write tests"
+    todo_id = res.split("ID ")[1].split(":")[0].strip()
 
-    get_res = todo_tool.execute_action("todo_get", todo_id=todo_id)
-    assert get_res["status_code"] == 200
-    assert get_res["todo"]["title"] == "Write tests"
-    assert get_res["todo"]["description"] == "Write pytest cases"
+    get_res = todo_tool.execute_action("get", todo_id=todo_id)
+    assert "Error" not in get_res
+    assert "Write tests" in get_res
 
 
 def test_get_all_todos(todo_tool: TodoListTool):
-    todo_tool.execute_action("todo_create", title="Task 1")
-    todo_tool.execute_action("todo_create", title="Task 2")
+    todo_tool.execute_action("create", title="Task 1")
+    todo_tool.execute_action("create", title="Task 2")
 
-    list_res = todo_tool.execute_action("todo_list")
-    assert list_res["status_code"] == 200
-    titles = [todo["title"] for todo in list_res["todos"]]
-    assert "Task 1" in titles
-    assert "Task 2" in titles
+    list_res = todo_tool.execute_action("list")
+    assert "Task 1" in list_res
+    assert "Task 2" in list_res
 
 
 def test_update_todo(todo_tool: TodoListTool):
-    create_res = todo_tool.execute_action("todo_create", title="Initial Title")
-    todo_id = create_res["todo_id"]
+    create_res = todo_tool.execute_action("create", title="Initial Title")
+    todo_id = create_res.split("ID ")[1].split(":")[0].strip()
 
-    update_res = todo_tool.execute_action("todo_update", todo_id=todo_id, updates={"title": "Updated Title", "status": "done"})
-    assert update_res["status_code"] == 200
+    update_res = todo_tool.execute_action("update", todo_id=todo_id, title="Updated Title")
+    assert "updated" in update_res.lower()
+    assert "Updated Title" in update_res
 
-    get_res = todo_tool.execute_action("todo_get", todo_id=todo_id)
-    assert get_res["todo"]["title"] == "Updated Title"
-    assert get_res["todo"]["status"] == "done"
+    get_res = todo_tool.execute_action("get", todo_id=todo_id)
+    assert "Updated Title" in get_res
+
+
+def test_complete_todo(todo_tool: TodoListTool):
+    create_res = todo_tool.execute_action("create", title="To Complete")
+    todo_id = create_res.split("ID ")[1].split(":")[0].strip()
+
+    # Check initial status is open
+    get_res = todo_tool.execute_action("get", todo_id=todo_id)
+    assert "open" in get_res
+
+    # Mark as completed
+    complete_res = todo_tool.execute_action("complete", todo_id=todo_id)
+    assert "completed" in complete_res.lower()
+
+    # Verify status changed to completed
+    get_res = todo_tool.execute_action("get", todo_id=todo_id)
+    assert "completed" in get_res
 
 
 def test_delete_todo(todo_tool: TodoListTool):
-    create_res = todo_tool.execute_action("todo_create", title="To Delete")
-    todo_id = create_res["todo_id"]
+    create_res = todo_tool.execute_action("create", title="To Delete")
+    todo_id = create_res.split("ID ")[1].split(":")[0].strip()
 
-    delete_res = todo_tool.execute_action("todo_delete", todo_id=todo_id)
-    assert delete_res["status_code"] == 200
+    delete_res = todo_tool.execute_action("delete", todo_id=todo_id)
+    assert "deleted" in delete_res.lower()
 
-    get_res = todo_tool.execute_action("todo_get", todo_id=todo_id)
-    assert get_res["status_code"] == 404
+    get_res = todo_tool.execute_action("get", todo_id=todo_id)
+    assert "Error" in get_res
+    assert "not found" in get_res
 
 
 def test_isolation_and_default_tool_id(monkeypatch):
     """Ensure todos are isolated by tool_id and user_id."""
+    # Reset the MongoDB client cache to ensure our mock is used
+    from application.core.mongo_db import MongoDB
+    MongoDB._client = None
+
     fake_collection = FakeCollection()
     fake_client = {settings.MONGO_DB_NAME: {"todos": fake_collection}}
     monkeypatch.setattr("application.core.mongo_db.MongoDB.get_client", lambda: fake_client)
@@ -130,17 +154,20 @@ def test_isolation_and_default_tool_id(monkeypatch):
     tool1 = TodoListTool({"tool_id": "tool_1"}, user_id="u1")
     tool2 = TodoListTool({"tool_id": "tool_2"}, user_id="u1")
 
-    r1_create = tool1.execute_action("todo_create", title="from tool 1")
-    r2_create = tool2.execute_action("todo_create", title="from tool 2")
+    r1_create = tool1.execute_action("create", title="from tool 1")
+    r2_create = tool2.execute_action("create", title="from tool 2")
 
-    r1 = tool1.execute_action("todo_get", todo_id=r1_create["todo_id"])
-    r2 = tool2.execute_action("todo_get", todo_id=r2_create["todo_id"])
+    todo_id_1 = r1_create.split("ID ")[1].split(":")[0].strip()
+    todo_id_2 = r2_create.split("ID ")[1].split(":")[0].strip()
 
-    assert r1["status_code"] == 200
-    assert r1["todo"]["title"] == "from tool 1"
+    r1 = tool1.execute_action("get", todo_id=todo_id_1)
+    r2 = tool2.execute_action("get", todo_id=todo_id_2)
 
-    assert r2["status_code"] == 200
-    assert r2["todo"]["title"] == "from tool 2"
+    assert "Error" not in r1
+    assert "from tool 1" in r1
+
+    assert "Error" not in r2
+    assert "from tool 2" in r2
 
     # Same user, no tool_id → should default to same value
     t3 = TodoListTool({}, user_id="default_user")
@@ -149,8 +176,9 @@ def test_isolation_and_default_tool_id(monkeypatch):
     assert t3.tool_id == "default_default_user"
     assert t4.tool_id == "default_default_user"
 
-    create_res = t3.execute_action("todo_create", title="shared default")
-    r = t4.execute_action("todo_get", todo_id=create_res["todo_id"])
+    create_res = t3.execute_action("create", title="shared default")
+    todo_id = create_res.split("ID ")[1].split(":")[0].strip()
+    r = t4.execute_action("get", todo_id=todo_id)
 
-    assert r["status_code"] == 200
-    assert r["todo"]["title"] == "shared default"
+    assert "Error" not in r
+    assert "shared default" in r