diff --git a/tests/entrypoints/openai/parser/test_harmony_utils.py b/tests/entrypoints/openai/parser/test_harmony_utils.py
index 092e916f89..d2985264e0 100644
--- a/tests/entrypoints/openai/parser/test_harmony_utils.py
+++ b/tests/entrypoints/openai/parser/test_harmony_utils.py
@@ -2,11 +2,14 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
 import pytest
+from openai.types.responses import FunctionTool
 from openai_harmony import DeveloperContent, Message, Role
 
 from tests.entrypoints.openai.utils import verify_harmony_messages
+from vllm.entrypoints.openai.chat_completion.protocol import ChatCompletionToolsParam
 from vllm.entrypoints.openai.parser.harmony_utils import (
     auto_drop_analysis_messages,
+    create_tool_definition,
     extract_function_from_recipient,
     get_encoding,
     get_system_message,
@@ -20,6 +23,58 @@ from vllm.entrypoints.openai.responses.harmony import (
     response_previous_input_to_harmony,
 )
 
+_TOOL_PARAMETERS = {
+    "type": "object",
+    "properties": {"status": {"type": "string"}},
+    "required": ["status"],
+    "additionalProperties": False,
+}
+
+
+class TestCreateToolDefinition:
+    def test_chat_completion_omitted_description_defaults_to_empty_string(self):
+        tool = ChatCompletionToolsParam(
+            function={
+                "name": "report_status",
+                "parameters": _TOOL_PARAMETERS,
+            }
+        )
+
+        tool_definition = create_tool_definition(tool)
+
+        assert tool_definition.name == "report_status"
+        assert tool_definition.description == ""
+        assert tool_definition.parameters == _TOOL_PARAMETERS
+
+    def test_chat_completion_none_description_defaults_to_empty_string(self):
+        tool = ChatCompletionToolsParam(
+            function={
+                "name": "report_status",
+                "description": None,
+                "parameters": _TOOL_PARAMETERS,
+            }
+        )
+
+        tool_definition = create_tool_definition(tool)
+
+        assert tool_definition.name == "report_status"
+        assert tool_definition.description == ""
+        assert tool_definition.parameters == _TOOL_PARAMETERS
+
+    def test_response_tool_none_description_defaults_to_empty_string(self):
+        tool = FunctionTool(
+            name="report_status",
+            description=None,
+            parameters=_TOOL_PARAMETERS,
+            type="function",
+        )
+
+        tool_definition = create_tool_definition(tool)
+
+        assert tool_definition.name == "report_status"
+        assert tool_definition.description == ""
+        assert tool_definition.parameters == _TOOL_PARAMETERS
+
 
 class TestIsFunctionRecipient:
     @pytest.mark.parametrize(
diff --git a/vllm/entrypoints/openai/parser/harmony_utils.py b/vllm/entrypoints/openai/parser/harmony_utils.py
index cbd1f6bb78..771faabe60 100644
--- a/vllm/entrypoints/openai/parser/harmony_utils.py
+++ b/vllm/entrypoints/openai/parser/harmony_utils.py
@@ -150,12 +150,12 @@ def create_tool_definition(tool: ChatCompletionToolsParam | Tool):
     if isinstance(tool, ChatCompletionToolsParam):
         return ToolDescription.new(
             name=tool.function.name,
-            description=tool.function.description,
+            description=tool.function.description or "",
             parameters=tool.function.parameters,
         )
     return ToolDescription.new(
         name=tool.name,
-        description=tool.description,
+        description=tool.description or "",
         parameters=tool.parameters,
     )