diff --git a/src/google/adk/models/llm_request.py b/src/google/adk/models/llm_request.py
index 39fddef4..b83fd1d9 100644
--- a/src/google/adk/models/llm_request.py
+++ b/src/google/adk/models/llm_request.py
@@ -24,6 +24,24 @@ from pydantic import Field
 from ..tools.base_tool import BaseTool
 
 
+def _find_tool_with_function_declarations(
+    llm_request: LlmRequest,
+) -> Optional[types.Tool]:
+  """Find an existing Tool with function_declarations in the LlmRequest."""
+  # TODO: add individual tool with declaration and merge in google_llm.py
+  if not llm_request.config or not llm_request.config.tools:
+    return None
+
+  return next(
+      (
+          tool
+          for tool in llm_request.config.tools
+          if isinstance(tool, types.Tool) and tool.function_declarations
+      ),
+      None,
+  )
+
+
 class LlmRequest(BaseModel):
   """LLM request class that allows passing in tools, output schema and system
 
@@ -81,15 +99,26 @@ class LlmRequest(BaseModel):
       return
     declarations = []
     for tool in tools:
-      if isinstance(tool, BaseTool):
-        declaration = tool._get_declaration()
-      else:
-        declaration = tool.get_declaration()
+      declaration = tool._get_declaration()
       if declaration:
         declarations.append(declaration)
         self.tools_dict[tool.name] = tool
     if declarations:
-      self.config.tools.append(types.Tool(function_declarations=declarations))
+      if self.config.tools is None:
+        self.config.tools = []
+
+      # Find existing tool with function_declarations and append to it
+      if tool_with_function_declarations := _find_tool_with_function_declarations(
+          self
+      ):
+        if tool_with_function_declarations.function_declarations is None:
+          tool_with_function_declarations.function_declarations = []
+        tool_with_function_declarations.function_declarations.extend(
+            declarations
+        )
+      else:
+        # No existing tool with function_declarations, create new one
+        self.config.tools.append(types.Tool(function_declarations=declarations))
 
   def set_output_schema(self, base_model: type[BaseModel]) -> None:
     """Sets the output schema for the request.
diff --git a/src/google/adk/tools/base_tool.py b/src/google/adk/tools/base_tool.py
index 21f721fb..90c57539 100644
--- a/src/google/adk/tools/base_tool.py
+++ b/src/google/adk/tools/base_tool.py
@@ -125,30 +125,8 @@ class BaseTool(ABC):
       tool_context: The context of the tool.
       llm_request: The outgoing LLM request, mutable this method.
     """
-    if (function_declaration := self._get_declaration()) is None:
-      return
-
-    llm_request.tools_dict[self.name] = self
-    if tool_with_function_declarations := _find_tool_with_function_declarations(
-        llm_request
-    ):
-      if tool_with_function_declarations.function_declarations is None:
-        tool_with_function_declarations.function_declarations = []
-      tool_with_function_declarations.function_declarations.append(
-          function_declaration
-      )
-    else:
-      llm_request.config = (
-          types.GenerateContentConfig()
-          if not llm_request.config
-          else llm_request.config
-      )
-      llm_request.config.tools = (
-          [] if not llm_request.config.tools else llm_request.config.tools
-      )
-      llm_request.config.tools.append(
-          types.Tool(function_declarations=[function_declaration])
-      )
+    # Use the consolidated logic in LlmRequest.append_tools
+    llm_request.append_tools([self])
 
   @property
   def _api_variant(self) -> GoogleLLMVariant:
@@ -232,20 +210,3 @@ class BaseTool(ABC):
         else:
           logger.warning("Unsupported parsing for argument: %s.", param_name)
     return cls(**kwargs)
-
-
-def _find_tool_with_function_declarations(
-    llm_request: LlmRequest,
-) -> Optional[types.Tool]:
-  # TODO: add individual tool with declaration and merge in google_llm.py
-  if not llm_request.config or not llm_request.config.tools:
-    return None
-
-  return next(
-      (
-          tool
-          for tool in llm_request.config.tools
-          if isinstance(tool, types.Tool) and tool.function_declarations
-      ),
-      None,
-  )
diff --git a/tests/unittests/models/test_llm_request.py b/tests/unittests/models/test_llm_request.py
new file mode 100644
index 00000000..78942296
--- /dev/null
+++ b/tests/unittests/models/test_llm_request.py
@@ -0,0 +1,310 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tests for LlmRequest functionality."""
+
+import asyncio
+from typing import Optional
+
+from google.adk.agents.invocation_context import InvocationContext
+from google.adk.agents.sequential_agent import SequentialAgent
+from google.adk.models.llm_request import LlmRequest
+from google.adk.sessions.in_memory_session_service import InMemorySessionService
+from google.adk.tools.base_tool import BaseTool
+from google.adk.tools.function_tool import FunctionTool
+from google.adk.tools.tool_context import ToolContext
+from google.genai import types
+import pytest
+
+
+def dummy_tool(query: str) -> str:
+  """A dummy tool for testing."""
+  return f'Searched for: {query}'
+
+
+def test_append_tools_with_none_config_tools():
+  """Test that append_tools initializes config.tools when it's None."""
+  request = LlmRequest()
+
+  # Initially config.tools should be None
+  assert request.config.tools is None
+
+  # Create a tool to append
+  tool = FunctionTool(func=dummy_tool)
+
+  # This should not raise an AttributeError
+  request.append_tools([tool])
+
+  # Now config.tools should be initialized and contain the tool
+  assert request.config.tools is not None
+  assert len(request.config.tools) == 1
+  assert len(request.config.tools[0].function_declarations) == 1
+  assert request.config.tools[0].function_declarations[0].name == 'dummy_tool'
+
+  # Tool should also be in tools_dict
+  assert 'dummy_tool' in request.tools_dict
+  assert request.tools_dict['dummy_tool'] == tool
+
+
+def test_append_tools_with_existing_tools():
+  """Test that append_tools works correctly when config.tools already exists."""
+  request = LlmRequest()
+
+  # Pre-initialize config.tools with an existing tool
+  existing_declaration = types.FunctionDeclaration(
+      name='existing_tool', description='An existing tool', parameters={}
+  )
+  request.config.tools = [
+      types.Tool(function_declarations=[existing_declaration])
+  ]
+
+  # Create a new tool to append
+  tool = FunctionTool(func=dummy_tool)
+
+  # Append the new tool
+  request.append_tools([tool])
+
+  # Should still have 1 tool but now with 2 function declarations
+  assert len(request.config.tools) == 1
+  assert len(request.config.tools[0].function_declarations) == 2
+
+  # Verify both declarations are present
+  decl_names = {
+      decl.name for decl in request.config.tools[0].function_declarations
+  }
+  assert decl_names == {'existing_tool', 'dummy_tool'}
+
+
+def test_append_tools_empty_list():
+  """Test that append_tools handles empty list correctly."""
+  request = LlmRequest()
+
+  # This should not modify anything
+  request.append_tools([])
+
+  # config.tools should still be None
+  assert request.config.tools is None
+  assert len(request.tools_dict) == 0
+
+
+def test_append_tools_tool_with_no_declaration():
+  """Test append_tools with a BaseTool that returns None from _get_declaration."""
+  from google.adk.tools.base_tool import BaseTool
+
+  request = LlmRequest()
+
+  # Create a mock tool that inherits from BaseTool and returns None for declaration
+  class NoDeclarationTool(BaseTool):
+
+    def __init__(self):
+      super().__init__(
+          name='no_decl_tool', description='A tool with no declaration'
+      )
+
+    def _get_declaration(self):
+      return None
+
+  tool = NoDeclarationTool()
+
+  # This should not add anything to config.tools but should handle gracefully
+  request.append_tools([tool])
+
+  # config.tools should still be None since no declarations were added
+  assert request.config.tools is None
+  # tools_dict should be empty since no valid declaration
+  assert len(request.tools_dict) == 0
+
+
+def test_append_tools_consolidates_declarations_in_single_tool():
+  """Test that append_tools puts all function declarations in a single Tool."""
+  request = LlmRequest()
+
+  # Create multiple tools
+  tool1 = FunctionTool(func=dummy_tool)
+
+  def another_tool(param: str) -> str:
+    return f'Another: {param}'
+
+  def third_tool(value: int) -> int:
+    return value * 2
+
+  tool2 = FunctionTool(func=another_tool)
+  tool3 = FunctionTool(func=third_tool)
+
+  # Append all tools at once
+  request.append_tools([tool1, tool2, tool3])
+
+  # Should have exactly 1 Tool with 3 function declarations
+  assert len(request.config.tools) == 1
+  assert len(request.config.tools[0].function_declarations) == 3
+
+  # Verify all tools are in tools_dict
+  assert len(request.tools_dict) == 3
+  assert 'dummy_tool' in request.tools_dict
+  assert 'another_tool' in request.tools_dict
+  assert 'third_tool' in request.tools_dict
+
+
+async def _create_tool_context() -> ToolContext:
+  """Helper to create a ToolContext for testing."""
+  session_service = InMemorySessionService()
+  session = await session_service.create_session(
+      app_name='test_app', user_id='test_user'
+  )
+  agent = SequentialAgent(name='test_agent')
+  invocation_context = InvocationContext(
+      invocation_id='invocation_id',
+      agent=agent,
+      session=session,
+      session_service=session_service,
+  )
+  return ToolContext(invocation_context)
+
+
+class _MockTool(BaseTool):
+  """Mock tool for testing process_llm_request behavior."""
+
+  def __init__(self, name: str):
+    super().__init__(name=name, description=f'Mock tool {name}')
+
+  def _get_declaration(self) -> Optional[types.FunctionDeclaration]:
+    return types.FunctionDeclaration(
+        name=self.name,
+        description=self.description,
+        parameters=types.Schema(type=types.Type.STRING, title='param'),
+    )
+
+
+@pytest.mark.asyncio
+async def test_process_llm_request_consolidates_declarations_in_single_tool():
+  """Test that multiple process_llm_request calls consolidate in single Tool."""
+  request = LlmRequest()
+  tool_context = await _create_tool_context()
+
+  # Create multiple tools
+  tool1 = _MockTool('tool1')
+  tool2 = _MockTool('tool2')
+  tool3 = _MockTool('tool3')
+
+  # Process each tool individually (simulating what happens in real usage)
+  await tool1.process_llm_request(
+      tool_context=tool_context, llm_request=request
+  )
+  await tool2.process_llm_request(
+      tool_context=tool_context, llm_request=request
+  )
+  await tool3.process_llm_request(
+      tool_context=tool_context, llm_request=request
+  )
+
+  # Should have exactly 1 Tool with 3 function declarations
+  assert len(request.config.tools) == 1
+  assert len(request.config.tools[0].function_declarations) == 3
+
+  # Verify all function declaration names
+  decl_names = [
+      decl.name for decl in request.config.tools[0].function_declarations
+  ]
+  assert 'tool1' in decl_names
+  assert 'tool2' in decl_names
+  assert 'tool3' in decl_names
+
+  # Verify all tools are in tools_dict
+  assert len(request.tools_dict) == 3
+  assert 'tool1' in request.tools_dict
+  assert 'tool2' in request.tools_dict
+  assert 'tool3' in request.tools_dict
+
+
+@pytest.mark.asyncio
+async def test_append_tools_and_process_llm_request_consistent_behavior():
+  """Test that append_tools and process_llm_request produce same structure."""
+  tool_context = await _create_tool_context()
+
+  # Test 1: Using append_tools
+  request1 = LlmRequest()
+  tool1 = _MockTool('tool1')
+  tool2 = _MockTool('tool2')
+  tool3 = _MockTool('tool3')
+  request1.append_tools([tool1, tool2, tool3])
+
+  # Test 2: Using process_llm_request
+  request2 = LlmRequest()
+  tool4 = _MockTool('tool1')  # Same names for comparison
+  tool5 = _MockTool('tool2')
+  tool6 = _MockTool('tool3')
+  await tool4.process_llm_request(
+      tool_context=tool_context, llm_request=request2
+  )
+  await tool5.process_llm_request(
+      tool_context=tool_context, llm_request=request2
+  )
+  await tool6.process_llm_request(
+      tool_context=tool_context, llm_request=request2
+  )
+
+  # Both approaches should produce identical structure
+  assert len(request1.config.tools) == len(request2.config.tools) == 1
+  assert len(request1.config.tools[0].function_declarations) == 3
+  assert len(request2.config.tools[0].function_declarations) == 3
+
+  # Function declaration names should match
+  decl_names1 = {
+      decl.name for decl in request1.config.tools[0].function_declarations
+  }
+  decl_names2 = {
+      decl.name for decl in request2.config.tools[0].function_declarations
+  }
+  assert decl_names1 == decl_names2 == {'tool1', 'tool2', 'tool3'}
+
+
+def test_multiple_append_tools_calls_consolidate():
+  """Test that multiple append_tools calls add to the same Tool."""
+  request = LlmRequest()
+
+  # First call to append_tools
+  tool1 = FunctionTool(func=dummy_tool)
+  request.append_tools([tool1])
+
+  # Should have 1 tool with 1 declaration
+  assert len(request.config.tools) == 1
+  assert len(request.config.tools[0].function_declarations) == 1
+  assert request.config.tools[0].function_declarations[0].name == 'dummy_tool'
+
+  # Second call to append_tools with different tools
+  def another_tool(param: str) -> str:
+    return f'Another: {param}'
+
+  def third_tool(value: int) -> int:
+    return value * 2
+
+  tool2 = FunctionTool(func=another_tool)
+  tool3 = FunctionTool(func=third_tool)
+  request.append_tools([tool2, tool3])
+
+  # Should still have 1 tool but now with 3 declarations
+  assert len(request.config.tools) == 1
+  assert len(request.config.tools[0].function_declarations) == 3
+
+  # Verify all declaration names are present
+  decl_names = {
+      decl.name for decl in request.config.tools[0].function_declarations
+  }
+  assert decl_names == {'dummy_tool', 'another_tool', 'third_tool'}
+
+  # Verify all tools are in tools_dict
+  assert len(request.tools_dict) == 3
+  assert 'dummy_tool' in request.tools_dict
+  assert 'another_tool' in request.tools_dict
+  assert 'third_tool' in request.tools_dict