diff --git a/src/google/adk/agents/callback_context.py b/src/google/adk/agents/callback_context.py
index 9d6e311..724d49a 100644
--- a/src/google/adk/agents/callback_context.py
+++ b/src/google/adk/agents/callback_context.py
@@ -60,11 +60,6 @@ class CallbackContext(ReadonlyContext):
     """
     return self._state
 
-  @property
-  def user_content(self) -> Optional[types.Content]:
-    """The user content that started this invocation. READONLY field."""
-    return self._invocation_context.user_content
-
   async def load_artifact(
       self, filename: str, version: Optional[int] = None
   ) -> Optional[types.Part]:
diff --git a/src/google/adk/agents/llm_agent.py b/src/google/adk/agents/llm_agent.py
index 4d4ceae..0076c6a 100644
--- a/src/google/adk/agents/llm_agent.py
+++ b/src/google/adk/agents/llm_agent.py
@@ -15,7 +15,15 @@
 from __future__ import annotations
 
 import logging
-from typing import Any, AsyncGenerator, Awaitable, Callable, Literal, Optional, Union
+from typing import (
+    Any,
+    AsyncGenerator,
+    Awaitable,
+    Callable,
+    Literal,
+    Optional,
+    Union,
+)
 
 from google.genai import types
 from pydantic import BaseModel
@@ -38,6 +46,7 @@ from ..models.llm_response import LlmResponse
 from ..models.registry import LLMRegistry
 from ..planners.base_planner import BasePlanner
 from ..tools.base_tool import BaseTool
+from ..tools.base_toolset import BaseToolset
 from ..tools.function_tool import FunctionTool
 from ..tools.tool_context import ToolContext
 from .base_agent import BaseAgent
@@ -89,18 +98,19 @@ AfterToolCallback: TypeAlias = Union[
 
 InstructionProvider: TypeAlias = Callable[[ReadonlyContext], str]
 
-ToolUnion: TypeAlias = Union[Callable, BaseTool]
+ToolUnion: TypeAlias = Union[Callable, BaseTool, BaseToolset]
 ExamplesUnion = Union[list[Example], BaseExampleProvider]
 
 
-def _convert_tool_union_to_tool(
-    tool_union: ToolUnion,
-) -> BaseTool:
-  return (
-      tool_union
-      if isinstance(tool_union, BaseTool)
-      else FunctionTool(tool_union)
-  )
+async def _convert_tool_union_to_tools(
+    tool_union: ToolUnion, ctx: ReadonlyContext
+) -> list[BaseTool]:
+  if isinstance(tool_union, BaseTool):
+    return [tool_union]
+  if isinstance(tool_union, Callable):
+    return [FunctionTool(func=tool_union)]
+
+  return await tool_union.get_tools(ctx)
 
 
 class LlmAgent(BaseAgent):
@@ -312,13 +322,17 @@ class LlmAgent(BaseAgent):
     else:
       return self.global_instruction(ctx)
 
-  @property
-  def canonical_tools(self) -> list[BaseTool]:
-    """The resolved self.tools field as a list of BaseTool.
+  async def canonical_tools(
+      self, ctx: ReadonlyContext = None
+  ) -> list[BaseTool]:
+    """The resolved self.tools field as a list of BaseTool based on the context.
 
     This method is only for use by Agent Development Kit.
     """
-    return [_convert_tool_union_to_tool(tool) for tool in self.tools]
+    resolved_tools = []
+    for tool_union in self.tools:
+      resolved_tools.extend(await _convert_tool_union_to_tools(tool_union, ctx))
+    return resolved_tools
 
   @property
   def canonical_before_model_callbacks(
diff --git a/src/google/adk/agents/readonly_context.py b/src/google/adk/agents/readonly_context.py
index fb373cc..928e2d1 100644
--- a/src/google/adk/agents/readonly_context.py
+++ b/src/google/adk/agents/readonly_context.py
@@ -15,10 +15,11 @@
 from __future__ import annotations
 
 from types import MappingProxyType
-from typing import Any
+from typing import Any, Optional
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
+  from google.genai import types
   from .invocation_context import InvocationContext
 
 
@@ -30,6 +31,11 @@ class ReadonlyContext:
   ) -> None:
     self._invocation_context = invocation_context
 
+  @property
+  def user_content(self) -> Optional[types.Content]:
+    """The user content that started this invocation. READONLY field."""
+    return self._invocation_context.user_content
+
   @property
   def invocation_id(self) -> str:
     """The current invocation id."""
diff --git a/src/google/adk/auth/auth_preprocessor.py b/src/google/adk/auth/auth_preprocessor.py
index 9a2f355..8ad30b7 100644
--- a/src/google/adk/auth/auth_preprocessor.py
+++ b/src/google/adk/auth/auth_preprocessor.py
@@ -20,6 +20,7 @@ from typing import TYPE_CHECKING
 from typing_extensions import override
 
 from ..agents.invocation_context import InvocationContext
+from ..agents.readonly_context import ReadonlyContext
 from ..events.event import Event
 from ..flows.llm_flows import functions
 from ..flows.llm_flows._base_llm_processor import BaseLlmRequestProcessor
@@ -105,7 +106,12 @@ class _AuthLlmRequestProcessor(BaseLlmRequestProcessor):
             function_response_event = await functions.handle_function_calls_async(
                 invocation_context,
                 event,
-                {tool.name: tool for tool in agent.canonical_tools},
+                {
+                    tool.name: tool
+                    for tool in await agent.canonical_tools(
+                        ReadonlyContext(invocation_context)
+                    )
+                },
                 # there could be parallel function calls that require auth
                 # auth response would be a dict keyed by function call id
                 tools_to_resume,
diff --git a/src/google/adk/cli/agent_graph.py b/src/google/adk/cli/agent_graph.py
index ebc6191..c1b5fa5 100644
--- a/src/google/adk/cli/agent_graph.py
+++ b/src/google/adk/cli/agent_graph.py
@@ -35,7 +35,7 @@ else:
   retrieval_tool_module_loaded = True
 
 
-def build_graph(graph, agent: BaseAgent, highlight_pairs):
+async def build_graph(graph, agent: BaseAgent, highlight_pairs):
   dark_green = '#0F5223'
   light_green = '#69CB87'
   light_gray = '#cccccc'
@@ -133,12 +133,12 @@ def build_graph(graph, agent: BaseAgent, highlight_pairs):
     build_graph(graph, sub_agent, highlight_pairs)
     draw_edge(agent.name, sub_agent.name)
   if isinstance(agent, LlmAgent):
-    for tool in agent.canonical_tools:
+    for tool in await agent.canonical_tools():
       draw_node(tool)
       draw_edge(agent.name, get_node_name(tool))
 
 
-def get_agent_graph(root_agent, highlights_pairs, image=False):
+async def get_agent_graph(root_agent, highlights_pairs, image=False):
   print('build graph')
   graph = graphviz.Digraph(graph_attr={'rankdir': 'LR', 'bgcolor': '#333537'})
   build_graph(graph, root_agent, highlights_pairs)
diff --git a/src/google/adk/cli/fast_api.py b/src/google/adk/cli/fast_api.py
index aa3de52..91cf3b3 100644
--- a/src/google/adk/cli/fast_api.py
+++ b/src/google/adk/cli/fast_api.py
@@ -24,13 +24,9 @@ import re
 import sys
 import traceback
 import typing
-from typing import Any
-from typing import List
-from typing import Literal
-from typing import Optional
+from typing import Any, List, Literal, Optional, Union
 
 import click
-from click import Tuple
 from fastapi import FastAPI
 from fastapi import HTTPException
 from fastapi import Query
@@ -53,9 +49,10 @@ from pydantic import ValidationError
 from starlette.types import Lifespan
 
 from ..agents import RunConfig
+from ..agents.base_agent import BaseAgent
 from ..agents.live_request_queue import LiveRequest
 from ..agents.live_request_queue import LiveRequestQueue
-from ..agents.llm_agent import Agent
+from ..agents.llm_agent import Agent, LlmAgent
 from ..agents.run_config import StreamingMode
 from ..artifacts import InMemoryArtifactService
 from ..events.event import Event
@@ -65,6 +62,7 @@ from ..sessions.database_session_service import DatabaseSessionService
 from ..sessions.in_memory_session_service import InMemorySessionService
 from ..sessions.session import Session
 from ..sessions.vertex_ai_session_service import VertexAiSessionService
+from ..tools.base_toolset import BaseToolset
 from .cli_eval import EVAL_SESSION_ID_PREFIX
 from .cli_eval import EvalMetric
 from .cli_eval import EvalMetricResult
@@ -163,6 +161,7 @@ def get_fast_api_app(
   trace.set_tracer_provider(provider)
 
   exit_stacks = []
+  toolsets_to_close: set[BaseToolset] = set()
 
   @asynccontextmanager
   async def internal_lifespan(app: FastAPI):
@@ -173,6 +172,8 @@ def get_fast_api_app(
         if exit_stacks:
           for stack in exit_stacks:
             await stack.aclose()
+        for toolset in toolsets_to_close:
+          await toolset.close()
     else:
       yield
 
@@ -673,7 +674,7 @@ def get_fast_api_app(
         from_name = event.author
         to_name = function_call.name
         function_call_highlights.append((from_name, to_name))
-        dot_graph = agent_graph.get_agent_graph(
+        dot_graph = await agent_graph.get_agent_graph(
             root_agent, function_call_highlights
         )
     elif function_responses:
@@ -682,13 +683,13 @@ def get_fast_api_app(
         from_name = function_response.name
         to_name = event.author
         function_responses_highlights.append((from_name, to_name))
-        dot_graph = agent_graph.get_agent_graph(
+        dot_graph = await agent_graph.get_agent_graph(
             root_agent, function_responses_highlights
         )
     else:
       from_name = event.author
       to_name = ""
-      dot_graph = agent_graph.get_agent_graph(
+      dot_graph = await agent_graph.get_agent_graph(
           root_agent, [(from_name, to_name)]
       )
     if dot_graph and isinstance(dot_graph, graphviz.Digraph):
@@ -766,6 +767,16 @@ def get_fast_api_app(
       for task in pending:
         task.cancel()
 
+  def _get_all_toolsets(agent: BaseAgent) -> set[BaseToolset]:
+    toolsets = set()
+    if isinstance(agent, LlmAgent):
+      for tool_union in agent.tools:
+        if isinstance(tool_union, BaseToolset):
+          toolsets.add(tool_union)
+    for sub_agent in agent.sub_agents:
+      toolsets.update(_get_all_toolsets(sub_agent))
+    return toolsets
+
   async def _get_root_agent_async(app_name: str) -> Agent:
     """Returns the root agent for the given app."""
     if app_name in root_agent_dict:
@@ -786,6 +797,7 @@ def get_fast_api_app(
         raise RuntimeError(f"error getting root agent, {e}") from e
 
     root_agent_dict[app_name] = root_agent
+    toolsets_to_close.update(_get_all_toolsets(root_agent))
     return root_agent
 
   async def _get_runner_async(app_name: str) -> Runner:
diff --git a/src/google/adk/evaluation/evaluation_generator.py b/src/google/adk/evaluation/evaluation_generator.py
index 779c8ad..09fcf26 100644
--- a/src/google/adk/evaluation/evaluation_generator.py
+++ b/src/google/adk/evaluation/evaluation_generator.py
@@ -258,7 +258,7 @@ class EvaluationGenerator:
     if not isinstance(agent, Agent) and not isinstance(agent, LlmAgent):
       return
 
-    for tool in agent.canonical_tools:
+    for tool in await agent.canonical_tools():
       tool_name = tool.name
       if tool_name in all_mock_tools:
         agent.before_tool_callback = callback
diff --git a/src/google/adk/flows/llm_flows/base_llm_flow.py b/src/google/adk/flows/llm_flows/base_llm_flow.py
index acf4d54..5268034 100644
--- a/src/google/adk/flows/llm_flows/base_llm_flow.py
+++ b/src/google/adk/flows/llm_flows/base_llm_flow.py
@@ -29,6 +29,7 @@ from ...agents.base_agent import BaseAgent
 from ...agents.callback_context import CallbackContext
 from ...agents.invocation_context import InvocationContext
 from ...agents.live_request_queue import LiveRequestQueue
+from ...agents.readonly_context import ReadonlyContext
 from ...agents.run_config import StreamingMode
 from ...agents.transcription_entry import TranscriptionEntry
 from ...events.event import Event
@@ -296,7 +297,9 @@ class BaseLlmFlow(ABC):
         yield event
 
     # Run processors for tools.
-    for tool in agent.canonical_tools:
+    for tool in await agent.canonical_tools(
+        ReadonlyContext(invocation_context)
+    ):
       tool_context = ToolContext(invocation_context)
       await tool.process_llm_request(
           tool_context=tool_context, llm_request=llm_request
diff --git a/src/google/adk/runners.py b/src/google/adk/runners.py
index 1ec8631..529c467 100644
--- a/src/google/adk/runners.py
+++ b/src/google/adk/runners.py
@@ -18,9 +18,7 @@ import asyncio
 import logging
 import queue
 import threading
-from typing import AsyncGenerator
-from typing import Generator
-from typing import Optional
+from typing import AsyncGenerator, Generator, Optional
 
 from deprecated import deprecated
 from google.genai import types
@@ -391,7 +389,7 @@ class Runner:
             f'CFC is not supported for model: {model_name} in agent:'
             f' {self.agent.name}'
         )
-      if built_in_code_execution not in self.agent.canonical_tools:
+      if built_in_code_execution not in self.agent.canonical_tools():
         self.agent.tools.append(built_in_code_execution)
 
     return InvocationContext(
diff --git a/src/google/adk/tools/base_toolset.py b/src/google/adk/tools/base_toolset.py
new file mode 100644
index 0000000..d603a8e
--- /dev/null
+++ b/src/google/adk/tools/base_toolset.py
@@ -0,0 +1,56 @@
+from abc import ABC
+from abc import abstractmethod
+from typing import Protocol
+
+from google.adk.agents.readonly_context import ReadonlyContext
+from google.adk.tools.base_tool import BaseTool
+
+
+class ToolPredicate(Protocol):
+  """Base class for a predicate that defines the interface to decide whether a
+
+  tool should be exposed to LLM. Toolset implementer could consider whether to
+  accept such instance in the toolset's constructor and apply the predicate in
+  get_tools method.
+  """
+
+  def __call__(
+      self, tool: BaseTool, readonly_context: ReadonlyContext = None
+  ) -> bool:
+    """Decide whether the passed-in tool should be exposed to LLM based on the
+
+    current context. True if the tool is usable by the LLM.
+
+    It's used to filter tools in the toolset.
+    """
+
+
+class BaseToolset(ABC):
+  """Base class for toolset.
+
+  A toolset is a collection of tools that can be used by an agent.
+  """
+
+  @abstractmethod
+  async def get_tools(
+      self, readony_context: ReadonlyContext = None
+  ) -> list[BaseTool]:
+    """Return all tools in the toolset based on the provided context.
+
+    Args:
+      readony_context (ReadonlyContext, optional): Context used to filter tools
+        available to the agent. If None, all tools in the toolset are returned.
+
+    Returns:
+      list[BaseTool]: A list of tools available under the specified context.
+    """
+
+  @abstractmethod
+  async def close(self) -> None:
+    """Performs cleanup and releases resources held by the toolset.
+
+    NOTE: This method is invoked, for example, at the end of an agent server's
+    lifecycle or when the toolset is no longer needed. Implementations
+    should ensure that any open connections, files, or other managed
+    resources are properly released to prevent leaks.
+    """