diff --git a/src/google/adk/tools/openapi_tool/common/common.py b/src/google/adk/tools/openapi_tool/common/common.py
index 7187b1bd..1df3125e 100644
--- a/src/google/adk/tools/openapi_tool/common/common.py
+++ b/src/google/adk/tools/openapi_tool/common/common.py
@@ -64,11 +64,9 @@ class ApiParameter(BaseModel):
   required: bool = False
 
   def model_post_init(self, _: Any):
-    self.py_name = (
-        self.py_name
-        if self.py_name
-        else rename_python_keywords(_to_snake_case(self.original_name))
-    )
+    if not self.py_name:
+      inferred_name = rename_python_keywords(_to_snake_case(self.original_name))
+      self.py_name = inferred_name or self._default_py_name()
     if isinstance(self.param_schema, str):
       self.param_schema = Schema.model_validate_json(self.param_schema)
 
@@ -77,6 +75,16 @@ class ApiParameter(BaseModel):
     self.type_hint = TypeHintHelper.get_type_hint(self.param_schema)
     return self
 
+  def _default_py_name(self) -> str:
+    location_defaults = {
+        'body': 'body',
+        'query': 'query_param',
+        'path': 'path_param',
+        'header': 'header_param',
+        'cookie': 'cookie_param',
+    }
+    return location_defaults.get(self.param_location or '', 'value')
+
   @model_serializer
   def _serialize(self):
     return {
diff --git a/src/google/adk/tools/openapi_tool/openapi_spec_parser/operation_parser.py b/src/google/adk/tools/openapi_tool/openapi_spec_parser/operation_parser.py
index 06d692a2..326ff678 100644
--- a/src/google/adk/tools/openapi_tool/openapi_spec_parser/operation_parser.py
+++ b/src/google/adk/tools/openapi_tool/openapi_spec_parser/operation_parser.py
@@ -139,10 +139,19 @@ class OperationParser:
             )
         )
       else:
+        # Prefer explicit body name to avoid empty keys when schema lacks type
+        # information (e.g., oneOf/anyOf/allOf) while retaining legacy behavior
+        # for simple scalar types.
+        if schema and (schema.oneOf or schema.anyOf or schema.allOf):
+          param_name = 'body'
+        elif not schema or not schema.type:
+          param_name = 'body'
+        else:
+          param_name = ''
+
         self._params.append(
-            # Empty name for unnamed body param
             ApiParameter(
-                original_name='',
+                original_name=param_name,
                 param_location='body',
                 param_schema=schema,
                 description=description,
diff --git a/tests/unittests/tools/openapi_tool/common/test_common.py b/tests/unittests/tools/openapi_tool/common/test_common.py
index 47aeb79f..faece5be 100644
--- a/tests/unittests/tools/openapi_tool/common/test_common.py
+++ b/tests/unittests/tools/openapi_tool/common/test_common.py
@@ -74,6 +74,24 @@ class TestApiParameter:
     )
     assert param.py_name == 'param_in'
 
+  def test_api_parameter_uses_location_default_when_name_missing(self):
+    schema = Schema(type='string')
+    param = ApiParameter(
+        original_name='',
+        param_location='body',
+        param_schema=schema,
+    )
+    assert param.py_name == 'body'
+
+  def test_api_parameter_uses_value_default_when_location_unknown(self):
+    schema = Schema(type='integer')
+    param = ApiParameter(
+        original_name='',
+        param_location='',
+        param_schema=schema,
+    )
+    assert param.py_name == 'value'
+
   def test_api_parameter_custom_py_name(self):
     schema = Schema(type='integer')
     param = ApiParameter(
diff --git a/tests/unittests/tools/openapi_tool/openapi_spec_parser/test_operation_parser.py b/tests/unittests/tools/openapi_tool/openapi_spec_parser/test_operation_parser.py
index 26cb944a..83741c97 100644
--- a/tests/unittests/tools/openapi_tool/openapi_spec_parser/test_operation_parser.py
+++ b/tests/unittests/tools/openapi_tool/openapi_spec_parser/test_operation_parser.py
@@ -164,6 +164,40 @@ def test_process_request_body_no_name():
   assert parser._params[0].param_location == 'body'
 
 
+def test_process_request_body_one_of_schema_assigns_name():
+  """Ensures oneOf bodies result in a named parameter."""
+  operation = Operation(
+      operationId='one_of_request',
+      requestBody=RequestBody(
+          content={
+              'application/json': MediaType(
+                  schema=Schema(
+                      oneOf=[
+                          Schema(
+                              type='object',
+                              properties={
+                                  'type': Schema(type='string'),
+                                  'stage': Schema(type='string'),
+                              },
+                          )
+                      ],
+                      discriminator={'propertyName': 'type'},
+                  )
+              )
+          }
+      ),
+      responses={'200': Response(description='ok')},
+  )
+  parser = OperationParser(operation)
+  params = parser.get_parameters()
+  assert len(params) == 1
+  assert params[0].original_name == 'body'
+  assert params[0].py_name == 'body'
+  schema = parser.get_json_schema()
+  assert 'body' in schema['properties']
+  assert '' not in schema['properties']
+
+
 def test_process_request_body_empty_object():
   """Test _process_request_body with a schema that is of type object but with no properties."""
   operation = Operation(