feat: Support MCP prompts

Add support for MCP prompts via the McpInstructionProvider class, which can be specified as an agent's instruction.

Co-authored-by: Kathy Wu <wukathy@google.com>
PiperOrigin-RevId: 828166051

src/google/adk/agents/__init__.py

@@ -12,6 +12,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import logging
+import sys
+
 from .base_agent import BaseAgent
 from .invocation_context import InvocationContext
 from .live_request_queue import LiveRequest
@@ -35,3 +38,16 @@ __all__ = [
     'LiveRequestQueue',
     'RunConfig',
 ]
+
+if sys.version_info < (3, 10):
+  logger = logging.getLogger('google_adk.' + __name__)
+  logger.warning(
+      'MCP requires Python 3.10 or above. Please upgrade your Python'
+      ' version in order to use it.'
+  )
+else:
+  from .mcp_instruction_provider import McpInstructionProvider
+
+  __all__.extend([
+      'McpInstructionProvider',
+  ])

src/google/adk/agents/mcp_instruction_provider.py

@@ -0,0 +1,107 @@
+# 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.
+
+"""Provides instructions to an agent by fetching prompts from an MCP server."""
+
+from __future__ import annotations
+
+import logging
+import sys
+from typing import Any
+from typing import Dict
+from typing import TextIO
+
+from .llm_agent import InstructionProvider
+from .readonly_context import ReadonlyContext
+
+# Attempt to import MCP Session Manager from the MCP library, and hints user to
+# upgrade their Python version to 3.10 if it fails.
+try:
+  from mcp import types
+
+  from ..tools.mcp_tool.mcp_session_manager import MCPSessionManager
+except ImportError as e:
+  if sys.version_info < (3, 10):
+    raise ImportError(
+        "MCP Session Manager requires Python 3.10 or above. Please upgrade"
+        " your Python version."
+    ) from e
+  else:
+    raise e
+
+
+class McpInstructionProvider(InstructionProvider):
+  """Fetches agent instructions from an MCP server."""
+
+  def __init__(
+      self,
+      connection_params: Any,
+      prompt_name: str,
+      errlog: TextIO = sys.stderr,
+  ):
+    """Initializes the McpInstructionProvider.
+
+    Args:
+        connection_params: Parameters for connecting to the MCP server.
+        prompt_name: The name of the MCP Prompt to fetch.
+        errlog: TextIO stream for error logging.
+    """
+    self._connection_params = connection_params
+    self._errlog = errlog or logging.getLogger(__name__)
+    self._mcp_session_manager = MCPSessionManager(
+        connection_params=self._connection_params,
+        errlog=self._errlog,
+    )
+    self.prompt_name = prompt_name
+
+  async def __call__(self, context: ReadonlyContext) -> str:
+    """Fetches the instruction from the MCP server.
+
+    Args:
+        context: The read-only context of the agent.
+
+    Returns:
+        The instruction string.
+    """
+    session = await self._mcp_session_manager.create_session()
+    # Fetch prompt definition to get the required argument names
+    prompt_definitions = await session.list_prompts()
+    prompt_definition = next(
+        (p for p in prompt_definitions.prompts if p.name == self.prompt_name),
+        None,
+    )
+
+    # Fetch arguments from context state if the prompt requires them
+    prompt_args: Dict[str, Any] = {}
+    if prompt_definition and prompt_definition.arguments:
+      arg_names = {arg.name for arg in prompt_definition.arguments}
+      prompt_args = {
+          k: v for k, v in (context.state or {}).items() if k in arg_names
+      }
+
+    # Fetch the specific prompt by name with arguments from context state
+    prompt_result: types.GetPromptResult = await session.get_prompt(
+        self.prompt_name, arguments=prompt_args
+    )
+
+    if prompt_result and prompt_result.messages:
+      # Concatenate content of all messages to form the instruction.
+      instruction = "".join(
+          message.content.text
+          for message in prompt_result.messages
+          if message.content.type == "text"
+      )
+      return instruction
+    else:
+      raise ValueError(f"Failed to load MCP prompt '{self.prompt_name}'.")