diff --git a/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py b/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py
index 5cd02293f14..51362106000 100644
--- a/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py
+++ b/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py
@@ -680,6 +680,13 @@ class VertexGeminiConfig(VertexAIBaseConfig, BaseConfig):
                     f"Gemini: Transforming OpenAI-style '{tool['type']}' tool to googleSearch"
                 )
                 tool = {VertexToolName.GOOGLE_SEARCH.value: {}}
+            elif tool.get("type") == "namespace" and (
+                not tool.get("description") or not tool.get("parameters")
+            ):
+                raise ValueError(
+                    "Namespace tools require description and parameters before "
+                    "converting to Gemini function declarations"
+                )
             # Handle tools with 'type' field (OpenAI spec compliance) Ignore this field -> https://github.com/BerriAI/litellm/issues/14644#issuecomment-3342061838
             elif "type" in tool:
                 tool = {k: tool[k] for k in tool if k != "type"}
diff --git a/litellm/responses/litellm_completion_transformation/transformation.py b/litellm/responses/litellm_completion_transformation/transformation.py
index 697b27a4ece..e2afe3cb8ca 100644
--- a/litellm/responses/litellm_completion_transformation/transformation.py
+++ b/litellm/responses/litellm_completion_transformation/transformation.py
@@ -1388,6 +1388,14 @@ class LiteLLMCompletionResponsesConfig:
                 )
             elif tool.get("type") in ("function", "namespace"):
                 typed_tool = cast(FunctionToolParam, tool)
+                if tool.get("type") == "namespace" and (
+                    not typed_tool.get("description")
+                    or not typed_tool.get("parameters")
+                ):
+                    raise ValueError(
+                        "Responses API namespace tools require description and "
+                        "parameters before converting to Chat Completion tools"
+                    )
                 # Ensure parameters has "type": "object" as required by providers like Anthropic
                 parameters = dict(typed_tool.get("parameters", {}) or {})
                 if not parameters or "type" not in parameters:
diff --git a/tests/test_litellm/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py b/tests/test_litellm/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py
index 0d02521433a..c99b52805fb 100644
--- a/tests/test_litellm/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py
+++ b/tests/test_litellm/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py
@@ -2917,6 +2917,16 @@ def test_vertex_ai_function_declarations_with_other_tools_separate():
     assert func_tool["function_declarations"][0]["name"] == "get_weather"
 
 
+def test_vertex_ai_namespace_tool_without_schema_raises():
+    v = VertexGeminiConfig()
+
+    with pytest.raises(ValueError, match="Namespace tools require description"):
+        v._map_function(
+            value=[{"type": "namespace", "name": "mcp__node_repl"}],
+            optional_params={},
+        )
+
+
 def test_vertex_ai_single_tool_type_still_works():
     """
     Test that single tool type usage still works correctly (backward compatibility).
diff --git a/tests/test_litellm/responses/litellm_completion_transformation/test_litellm_completion_responses.py b/tests/test_litellm/responses/litellm_completion_transformation/test_litellm_completion_responses.py
index 8fcc1e64220..de2df14367b 100644
--- a/tests/test_litellm/responses/litellm_completion_transformation/test_litellm_completion_responses.py
+++ b/tests/test_litellm/responses/litellm_completion_transformation/test_litellm_completion_responses.py
@@ -1,6 +1,8 @@
 import os
 import sys
 
+import pytest
+
 sys.path.insert(
     0, os.path.abspath("../../..")
 )  # Adds the parent directory to the system path
@@ -1222,11 +1224,22 @@ class TestToolTransformation:
         assert result_tool["type"] == "function"
         assert result_tool["function"]["name"] == "mcp__node_repl"
         assert (
-            result_tool["function"]["description"]
-            == "Run JavaScript in the node REPL"
+            result_tool["function"]["description"] == "Run JavaScript in the node REPL"
         )
         assert result_tool["function"]["parameters"] == namespace_tool["parameters"]
 
+    def test_transform_namespace_tools_without_schema_raises(self):
+        """Name-only namespace tools cannot be converted into usable functions."""
+        namespace_tool = {
+            "type": "namespace",
+            "name": "mcp__node_repl",
+        }
+
+        with pytest.raises(ValueError, match="namespace tools require description"):
+            LiteLLMCompletionResponsesConfig.transform_responses_api_tools_to_chat_completion_tools(
+                tools=[namespace_tool]
+            )
+
     def test_transform_code_execution_tools(self):
         """Test that code_execution tools are passed through as-is"""
         code_execution_tool = {