feat: Add a load MCP resource tool

If the user specifies use_mcp_resources=True in their MCPToolset, the agent will be able to load resources with the load_mcp_resource_tool.

Co-authored-by: Kathy Wu <wukathy@google.com>
PiperOrigin-RevId: 866539602

tests/unittests/tools/mcp_tool/test_mcp_toolset.py

@@ -25,6 +25,7 @@ from unittest.mock import patch
 
 from google.adk.agents.readonly_context import ReadonlyContext
 from google.adk.auth.auth_credential import AuthCredential
+from google.adk.tools.load_mcp_resource_tool import LoadMcpResourceTool
 from google.adk.tools.mcp_tool.mcp_session_manager import MCPSessionManager
 from google.adk.tools.mcp_tool.mcp_session_manager import SseConnectionParams
 from google.adk.tools.mcp_tool.mcp_session_manager import StdioConnectionParams
@@ -81,6 +82,14 @@ class TestMcpToolset:
     assert toolset._errlog == sys.stderr
     assert toolset._auth_scheme is None
     assert toolset._auth_credential is None
+    assert toolset._use_mcp_resources is False
+
+  def test_init_with_use_mcp_resources(self):
+    """Test initialization with use_mcp_resources."""
+    toolset = McpToolset(
+        connection_params=self.mock_stdio_params, use_mcp_resources=True
+    )
+    assert toolset._use_mcp_resources is True
 
   def test_init_with_stdio_connection_params(self):
     """Test initialization with StdioConnectionParams."""
@@ -161,17 +170,21 @@ class TestMcpToolset:
         return_value=MockListToolsResult(mock_tools)
     )
 
-    toolset = McpToolset(connection_params=self.mock_stdio_params)
+    toolset = McpToolset(
+        connection_params=self.mock_stdio_params, use_mcp_resources=True
+    )
     toolset._mcp_session_manager = self.mock_session_manager
 
     tools = await toolset.get_tools()
 
-    assert len(tools) == 3
-    for tool in tools:
+    assert len(tools) == 4
+    for tool in tools[:3]:
       assert isinstance(tool, MCPTool)
+    assert isinstance(tools[3], LoadMcpResourceTool)
     assert tools[0].name == "tool1"
     assert tools[1].name == "tool2"
     assert tools[2].name == "tool3"
+    assert tools[3].name == "load_mcp_resource"
 
   @pytest.mark.asyncio
   async def test_get_tools_with_list_filter(self):
@@ -338,6 +351,7 @@ class TestMcpToolset:
     toolset = McpToolset(
         connection_params=mock_connection_params,
         tool_name_prefix="my_prefix",
+        use_mcp_resources=True,
     )
 
     # Replace the internal session manager with our mock
@@ -352,13 +366,15 @@ class TestMcpToolset:
     prefixed_tools = await toolset.get_tools_with_prefix()
 
     # Assert that the tools are prefixed correctly
-    assert len(prefixed_tools) == 2
+    assert len(prefixed_tools) == 3
     assert prefixed_tools[0].name == "my_prefix_tool1"
     assert prefixed_tools[1].name == "my_prefix_tool2"
+    assert prefixed_tools[2].name == "my_prefix_load_mcp_resource"
 
     # Assert that the original tools are not modified
     assert tools[0].name == "tool1"
     assert tools[1].name == "tool2"
+    assert tools[2].name == "load_mcp_resource"
 
   def test_init_with_progress_callback(self):
     """Test initialization with progress_callback."""

tests/unittests/tools/test_load_mcp_resource_tool.py

@@ -0,0 +1,165 @@
+# Copyright 2026 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.
+
+import base64
+import json
+from unittest.mock import AsyncMock
+from unittest.mock import Mock
+from unittest.mock import patch
+
+from google.adk.models.llm_request import LlmRequest
+from google.adk.tools.load_mcp_resource_tool import LoadMcpResourceTool
+from google.adk.tools.mcp_tool.mcp_toolset import McpToolset
+from google.adk.tools.tool_context import ToolContext
+from google.genai import types
+from mcp.types import BlobResourceContents
+from mcp.types import TextResourceContents
+import pytest
+
+
+class TestLoadMcpResourceTool:
+  """Test suite for LoadMcpResourceTool class."""
+
+  def setup_method(self):
+    """Set up test fixtures."""
+    self.mock_mcp_toolset = Mock(spec=McpToolset)
+    self.mock_tool_context = Mock(spec=ToolContext)
+
+  def test_init(self):
+    """Test initialization."""
+    tool = LoadMcpResourceTool(mcp_toolset=self.mock_mcp_toolset)
+    assert tool.name == "load_mcp_resource"
+    assert tool._mcp_toolset == self.mock_mcp_toolset
+
+  @pytest.mark.asyncio
+  async def test_run_async(self):
+    """Test run_async method."""
+    tool = LoadMcpResourceTool(mcp_toolset=self.mock_mcp_toolset)
+    args = {"resource_names": ["res1", "res2"]}
+    result = await tool.run_async(
+        args=args, tool_context=self.mock_tool_context
+    )
+
+    assert result["resource_names"] == ["res1", "res2"]
+    assert "temporarily inserted" in result["status"]
+
+  def test_get_declaration(self):
+    """Test _get_declaration method."""
+    tool = LoadMcpResourceTool(mcp_toolset=self.mock_mcp_toolset)
+    declaration = tool._get_declaration()
+
+    assert isinstance(declaration, types.FunctionDeclaration)
+    assert declaration.name == "load_mcp_resource"
+    # Basic schema check, precise structure depends on is_feature_enabled
+    # and implementation details which might vary.
+
+  @pytest.mark.asyncio
+  async def test_process_llm_request_injects_list(self):
+    """Test that resource list is injected when enabled."""
+    tool = LoadMcpResourceTool(mcp_toolset=self.mock_mcp_toolset)
+    llm_request = Mock(spec=LlmRequest)
+    llm_request.contents = []
+
+    # Mock list_resources
+    self.mock_mcp_toolset.list_resources = AsyncMock(
+        return_value=["res1", "res2"]
+    )
+
+    await tool.process_llm_request(
+        tool_context=self.mock_tool_context, llm_request=llm_request
+    )
+
+    llm_request.append_instructions.assert_called_once()
+    instructions = llm_request.append_instructions.call_args[0][0]
+    assert "res1" in instructions[0]
+    assert "res2" in instructions[0]
+
+  async def test_process_llm_request_loads_content_text(self):
+    """Test loading text resource content."""
+    tool = LoadMcpResourceTool(mcp_toolset=self.mock_mcp_toolset)
+    llm_request = Mock(spec=LlmRequest)
+    llm_request.contents = []
+
+    # Setup LLM request with function call response asking for "res1"
+    function_response = Mock()
+    function_response.name = "load_mcp_resource"
+    function_response.response = {"resource_names": ["res1"]}
+
+    part = Mock()
+    part.function_response = function_response
+
+    content = Mock()
+    content.parts = [part]
+    llm_request.contents = [content]
+
+    # Mock read_resource
+    text_content = TextResourceContents(
+        uri="file:///res1", mimeType="text/plain", text="hello content"
+    )
+    self.mock_mcp_toolset.read_resource = AsyncMock(return_value=[text_content])
+
+    await tool.process_llm_request(
+        tool_context=self.mock_tool_context, llm_request=llm_request
+    )
+
+    # Verify content was appended
+    assert len(llm_request.contents) == 2  # Original + new content
+    new_content = llm_request.contents[1]
+    assert new_content.role == "user"
+    assert len(new_content.parts) == 2
+    assert "Resource res1 is:" in new_content.parts[0].text
+    assert new_content.parts[1].text == "hello content"
+
+  @pytest.mark.asyncio
+  async def test_process_llm_request_loads_content_binary(self):
+    """Test loading binary resource content."""
+    tool = LoadMcpResourceTool(mcp_toolset=self.mock_mcp_toolset)
+    llm_request = Mock(spec=LlmRequest)
+    llm_request.contents = []
+
+    # Setup LLM request with function call response asking for "res1"
+    function_response = Mock()
+    function_response.name = "load_mcp_resource"
+    function_response.response = {"resource_names": ["res1"]}
+
+    part = Mock()
+    part.function_response = function_response
+
+    content = Mock()
+    content.parts = [part]
+    llm_request.contents = [content]
+
+    # Mock read_resource
+    blob_data = b"binary data"
+    blob_b64 = base64.b64encode(blob_data).decode("ascii")
+    blob_content = BlobResourceContents(
+        uri="file:///res1", mimeType="image/png", blob=blob_b64
+    )
+    self.mock_mcp_toolset.read_resource = AsyncMock(return_value=[blob_content])
+
+    await tool.process_llm_request(
+        tool_context=self.mock_tool_context, llm_request=llm_request
+    )
+
+    # Verify content was appended
+    assert len(llm_request.contents) == 2
+    new_content = llm_request.contents[1]
+    # Check that the second part is bytes
+    # Note: google.genai.types.Part.from_bytes creates a Part with inline_data
+    # Accessing it depends on the Part implementation.
+    # Since we are using real types.Part (not mocked), we can check attributes.
+    part = new_content.parts[1]
+    assert part.inline_data is not None
+    assert part.inline_data.mime_type == "image/png"
+    assert part.inline_data.data == blob_data