diff --git a/libs/vertexai/langchain_google_vertexai/functions_utils.py b/libs/vertexai/langchain_google_vertexai/functions_utils.py
index 1524d671..2bf56608 100644
--- a/libs/vertexai/langchain_google_vertexai/functions_utils.py
+++ b/libs/vertexai/langchain_google_vertexai/functions_utils.py
@@ -1,5 +1,5 @@
 import json
-from typing import Dict, List, Type, Union
+from typing import Any, Dict, List, Type, Union
 
 from langchain_core.exceptions import OutputParserException
 from langchain_core.output_parsers import BaseOutputParser
@@ -25,17 +25,7 @@ def _format_pydantic_to_vertex_function(
     return {
         "name": schema["title"],
         "description": schema.get("description", ""),
-        "parameters": {
-            "properties": {
-                k: {
-                    "type": v["type"],
-                    "description": v.get("description"),
-                }
-                for k, v in schema["properties"].items()
-            },
-            "required": schema["required"],
-            "type": schema["type"],
-        },
+        "parameters": _get_parameters_from_schema(schema=schema),
     }
 
 
@@ -48,17 +38,7 @@ def _format_tool_to_vertex_function(tool: BaseTool) -> FunctionDescription:
         return {
             "name": tool.name or schema["title"],
             "description": tool.description or schema["description"],
-            "parameters": {
-                "properties": {
-                    k: {
-                        "type": v["type"],
-                        "description": v.get("description"),
-                    }
-                    for k, v in schema["properties"].items()
-                },
-                "required": schema["required"],
-                "type": schema["type"],
-            },
+            "parameters": _get_parameters_from_schema(schema=schema),
         }
     else:
         return {
@@ -89,6 +69,37 @@ def _format_tools_to_vertex_tool(
     return [VertexTool(function_declarations=function_declarations)]
 
 
+def _get_parameters_from_schema(schema: Dict[str, Any]) -> Dict[str, Any]:
+    """Given a schema, format the parameters key to match VertexAI
+    expected input.
+
+    Args:
+        schema: Dictionary that must have the following keys.
+
+    Returns:
+        Dictionary with the formatted parameters.
+    """
+
+    parameters = {}
+
+    parameters["type"] = schema["type"]
+
+    if "required" in schema:
+        parameters["required"] = schema["required"]
+
+    schema_properties: Dict[str, Any] = schema.get("properties", {})
+
+    parameters["properties"] = {
+        parameter_name: {
+            "type": parameter_dict["type"],
+            "description": parameter_dict.get("description"),
+        }
+        for parameter_name, parameter_dict in schema_properties.items()
+    }
+
+    return parameters
+
+
 class PydanticFunctionsOutputParser(BaseOutputParser):
     """Parse an output as a pydantic object.
 
diff --git a/libs/vertexai/tests/unit_tests/test_function_utils.py b/libs/vertexai/tests/unit_tests/test_function_utils.py
new file mode 100644
index 00000000..c1248f2d
--- /dev/null
+++ b/libs/vertexai/tests/unit_tests/test_function_utils.py
@@ -0,0 +1,45 @@
+from langchain_core.tools import tool
+
+from langchain_google_vertexai.functions_utils import _format_tool_to_vertex_function
+
+
+def test_format_tool_to_vertex_function():
+    @tool
+    def get_datetime() -> str:
+        """Gets the current datetime"""
+        import datetime
+
+        return datetime.datetime.now().strftime("%Y-%m-%d")
+
+    schema = _format_tool_to_vertex_function(get_datetime)  # type: ignore
+
+    assert schema["name"] == "get_datetime"
+    assert schema["description"] == "get_datetime() -> str - Gets the current datetime"
+    assert "parameters" in schema
+    assert "required" not in schema["parameters"]
+
+    @tool
+    def sum_two_numbers(a: float, b: float) -> str:
+        """Sum two numbers 'a' and 'b'.
+
+        Returns:
+            a + b in string format
+        """
+        return str(a + b)
+
+    schema = _format_tool_to_vertex_function(sum_two_numbers)  # type: ignore
+
+    assert schema["name"] == "sum_two_numbers"
+    assert "parameters" in schema
+    assert len(schema["parameters"]["required"]) == 2
+
+    @tool
+    def do_something_optional(a: float, b: float = 0) -> str:
+        """Some description"""
+        return str(a + b)
+
+    schema = _format_tool_to_vertex_function(do_something_optional)  # type: ignore
+
+    assert schema["name"] == "do_something_optional"
+    assert "parameters" in schema
+    assert len(schema["parameters"]["required"]) == 1