feat: native async tool support

- add async support for tools
- add async tool tests
- improve tool decorator typing
- fix _run backward compatibility
- update docs and improve readability of docstrings

lib/crewai/src/crewai/tools/base_tool.py

@@ -2,9 +2,18 @@ from __future__ import annotations
 
 from abc import ABC, abstractmethod
 import asyncio
-from collections.abc import Callable
+from collections.abc import Awaitable, Callable
 from inspect import signature
-from typing import Any, cast, get_args, get_origin
+from typing import (
+    Any,
+    Generic,
+    ParamSpec,
+    TypeVar,
+    cast,
+    get_args,
+    get_origin,
+    overload,
+)
 
 from pydantic import (
     BaseModel,
@@ -14,6 +23,7 @@ from pydantic import (
     create_model,
     field_validator,
 )
+from typing_extensions import TypeIs
 
 from crewai.tools.structured_tool import CrewStructuredTool
 from crewai.utilities.printer import Printer
@@ -21,6 +31,19 @@ from crewai.utilities.printer import Printer
 
 _printer = Printer()
 
+P = ParamSpec("P")
+R = TypeVar("R", covariant=True)
+
+
+def _is_async_callable(func: Callable[..., Any]) -> bool:
+    """Check if a callable is async."""
+    return asyncio.iscoroutinefunction(func)
+
+
+def _is_awaitable(value: R | Awaitable[R]) -> TypeIs[Awaitable[R]]:
+    """Type narrowing check for awaitable values."""
+    return asyncio.iscoroutine(value) or asyncio.isfuture(value)
+
 
 class EnvVar(BaseModel):
     name: str
@@ -55,7 +78,7 @@ class BaseTool(BaseModel, ABC):
         default=False, description="Flag to check if the description has been updated."
     )
 
-    cache_function: Callable = Field(
+    cache_function: Callable[..., bool] = Field(
         default=lambda _args=None, _result=None: True,
         description="Function that will be used to determine if the tool should be cached, should return a boolean. If None, the tool will be cached.",
     )
@@ -123,6 +146,35 @@ class BaseTool(BaseModel, ABC):
 
         return result
 
+    async def arun(
+        self,
+        *args: Any,
+        **kwargs: Any,
+    ) -> Any:
+        """Execute the tool asynchronously.
+
+        Args:
+            *args: Positional arguments to pass to the tool.
+            **kwargs: Keyword arguments to pass to the tool.
+
+        Returns:
+            The result of the tool execution.
+        """
+        result = await self._arun(*args, **kwargs)
+        self.current_usage_count += 1
+        return result
+
+    async def _arun(
+        self,
+        *args: Any,
+        **kwargs: Any,
+    ) -> Any:
+        """Async implementation of the tool. Override for async support."""
+        raise NotImplementedError(
+            f"{self.__class__.__name__} does not implement _arun. "
+            "Override _arun for async support or use run() for sync execution."
+        )
+
     def reset_usage_count(self) -> None:
         """Reset the current usage count to zero."""
         self.current_usage_count = 0
@@ -133,7 +185,17 @@ class BaseTool(BaseModel, ABC):
         *args: Any,
         **kwargs: Any,
     ) -> Any:
-        """Here goes the actual implementation of the tool."""
+        """Sync implementation of the tool.
+
+        Subclasses must implement this method for synchronous execution.
+
+        Args:
+            *args: Positional arguments for the tool.
+            **kwargs: Keyword arguments for the tool.
+
+        Returns:
+            The result of the tool execution.
+        """
 
     def to_structured_tool(self) -> CrewStructuredTool:
         """Convert this tool to a CrewStructuredTool instance."""
@@ -239,21 +301,90 @@ class BaseTool(BaseModel, ABC):
 
         if args:
             args_str = ", ".join(BaseTool._get_arg_annotations(arg) for arg in args)
-            return f"{origin.__name__}[{args_str}]"
+            return str(f"{origin.__name__}[{args_str}]")
 
-        return origin.__name__
+        return str(origin.__name__)
 
 
-class Tool(BaseTool):
-    """The function that will be executed when the tool is called."""
+class Tool(BaseTool, Generic[P, R]):
+    """Tool that wraps a callable function.
 
-    func: Callable
 
-    def _run(self, *args: Any, **kwargs: Any) -> Any:
-        return self.func(*args, **kwargs)
+    Type Parameters:
+        P: ParamSpec capturing the function's parameters.
+        R: The return type of the function.
+    """
+
+    func: Callable[P, R | Awaitable[R]]
+
+    def run(self, *args: P.args, **kwargs: P.kwargs) -> R:
+        """Executes the tool synchronously.
+
+        Args:
+            *args: Positional arguments for the tool.
+            **kwargs: Keyword arguments for the tool.
+
+        Returns:
+            The result of the tool execution.
+        """
+        _printer.print(f"Using Tool: {self.name}", color="cyan")
+        result = self.func(*args, **kwargs)
+
+        if asyncio.iscoroutine(result):
+            result = asyncio.run(result)
+
+        self.current_usage_count += 1
+        return result  # type: ignore[return-value]
+
+    def _run(self, *args: P.args, **kwargs: P.kwargs) -> R:
+        """Executes the wrapped function.
+
+        Args:
+            *args: Positional arguments for the function.
+            **kwargs: Keyword arguments for the function.
+
+        Returns:
+            The result of the function execution.
+        """
+        return self.func(*args, **kwargs)  # type: ignore[return-value]
+
+    async def arun(self, *args: P.args, **kwargs: P.kwargs) -> R:
+        """Executes the tool asynchronously.
+
+        Args:
+            *args: Positional arguments for the tool.
+            **kwargs: Keyword arguments for the tool.
+
+        Returns:
+            The result of the tool execution.
+        """
+        result = await self._arun(*args, **kwargs)
+        self.current_usage_count += 1
+        return result
+
+    async def _arun(self, *args: P.args, **kwargs: P.kwargs) -> R:
+        """Executes the wrapped function asynchronously.
+
+        Args:
+            *args: Positional arguments for the function.
+            **kwargs: Keyword arguments for the function.
+
+        Returns:
+            The result of the async function execution.
+
+        Raises:
+            NotImplementedError: If the wrapped function is not async.
+        """
+        result = self.func(*args, **kwargs)
+        if _is_awaitable(result):
+            return await result
+        raise NotImplementedError(
+            f"{self.name} does not have an async function. "
+            "Use run() for sync execution or provide an async function."
+        )
 
     @classmethod
-    def from_langchain(cls, tool: Any) -> Tool:
+    def from_langchain(cls, tool: Any) -> Tool[..., Any]:
         """Create a Tool instance from a CrewStructuredTool.
 
         This method takes a CrewStructuredTool object and converts it into a
@@ -261,10 +392,10 @@ class Tool(BaseTool):
         attribute and infers the argument schema if not explicitly provided.
 
         Args:
-            tool (Any): The CrewStructuredTool object to be converted.
+            tool: The CrewStructuredTool object to be converted.
 
         Returns:
-            Tool: A new Tool instance created from the provided CrewStructuredTool.
+            A new Tool instance created from the provided CrewStructuredTool.
 
         Raises:
             ValueError: If the provided tool does not have a callable 'func' attribute.
@@ -308,37 +439,83 @@ class Tool(BaseTool):
 def to_langchain(
     tools: list[BaseTool | CrewStructuredTool],
 ) -> list[CrewStructuredTool]:
+    """Convert a list of tools to CrewStructuredTool instances."""
     return [t.to_structured_tool() if isinstance(t, BaseTool) else t for t in tools]
 
 
+P2 = ParamSpec("P2")
+R2 = TypeVar("R2")
+
+
+@overload
+def tool(func: Callable[P2, R2], /) -> Tool[P2, R2]: ...
+
+
+@overload
 def tool(
-    *args, result_as_answer: bool = False, max_usage_count: int | None = None
-) -> Callable:
-    """
-    Decorator to create a tool from a function.
+    name: str,
+    /,
+    *,
+    result_as_answer: bool = ...,
+    max_usage_count: int | None = ...,
+) -> Callable[[Callable[P2, R2]], Tool[P2, R2]]: ...
+
+
+@overload
+def tool(
+    *,
+    result_as_answer: bool = ...,
+    max_usage_count: int | None = ...,
+) -> Callable[[Callable[P2, R2]], Tool[P2, R2]]: ...
+
+
+def tool(
+    *args: Callable[P2, R2] | str,
+    result_as_answer: bool = False,
+    max_usage_count: int | None = None,
+) -> Tool[P2, R2] | Callable[[Callable[P2, R2]], Tool[P2, R2]]:
+    """Decorator to create a Tool from a function.
+
+    Can be used in three ways:
+    1. @tool - decorator without arguments, uses function name
+    2. @tool("name") - decorator with custom name
+    3. @tool(result_as_answer=True) - decorator with options
 
     Args:
-        *args: Positional arguments, either the function to decorate or the tool name.
-        result_as_answer: Flag to indicate if the tool result should be used as the final agent answer.
-        max_usage_count: Maximum number of times this tool can be used. None means unlimited usage.
+        *args: Either the function to decorate or a custom tool name.
+        result_as_answer: If True, the tool result becomes the final agent answer.
+        max_usage_count: Maximum times this tool can be used. None means unlimited.
+
+    Returns:
+        A Tool instance.
+
+    Example:
+        @tool
+        def greet(name: str) -> str:
+            '''Greet someone.'''
+            return f"Hello, {name}!"
+
+        result = greet.run("World")
     """
 
-    def _make_with_name(tool_name: str) -> Callable:
-        def _make_tool(f: Callable) -> BaseTool:
+    def _make_with_name(tool_name: str) -> Callable[[Callable[P2, R2]], Tool[P2, R2]]:
+        def _make_tool(f: Callable[P2, R2]) -> Tool[P2, R2]:
             if f.__doc__ is None:
                 raise ValueError("Function must have a docstring")
-            if f.__annotations__ is None:
+
+            func_annotations = getattr(f, "__annotations__", None)
+            if func_annotations is None:
                 raise ValueError("Function must have type annotations")
 
             class_name = "".join(tool_name.split()).title()
-            args_schema = cast(
+            tool_args_schema = cast(
                 type[PydanticBaseModel],
                 type(
                     class_name,
                     (PydanticBaseModel,),
                     {
                         "__annotations__": {
-                            k: v for k, v in f.__annotations__.items() if k != "return"
+                            k: v for k, v in func_annotations.items() if k != "return"
                         },
                     },
                 ),
@@ -348,10 +525,9 @@ def tool(
                 name=tool_name,
                 description=f.__doc__,
                 func=f,
-                args_schema=args_schema,
+                args_schema=tool_args_schema,
                 result_as_answer=result_as_answer,
                 max_usage_count=max_usage_count,
-                current_usage_count=0,
             )
 
         return _make_tool
@@ -360,4 +536,10 @@ def tool(
         return _make_with_name(args[0].__name__)(args[0])
     if len(args) == 1 and isinstance(args[0], str):
         return _make_with_name(args[0])
+    if len(args) == 0:
+
+        def decorator(f: Callable[P2, R2]) -> Tool[P2, R2]:
+            return _make_with_name(f.__name__)(f)
+
+        return decorator
     raise ValueError("Invalid arguments")

lib/crewai/src/crewai/tools/tool_usage.py

@@ -160,6 +160,251 @@ class ToolUsage:
 
         return f"{self._use(tool_string=tool_string, tool=tool, calling=calling)}"
 
+    async def ause(
+        self, calling: ToolCalling | InstructorToolCalling, tool_string: str
+    ) -> str:
+        """Execute a tool asynchronously.
+
+        Args:
+            calling: The tool calling information.
+            tool_string: The raw tool string from the agent.
+
+        Returns:
+            The result of the tool execution as a string.
+        """
+        if isinstance(calling, ToolUsageError):
+            error = calling.message
+            if self.agent and self.agent.verbose:
+                self._printer.print(content=f"\n\n{error}\n", color="red")
+            if self.task:
+                self.task.increment_tools_errors()
+            return error
+
+        try:
+            tool = self._select_tool(calling.tool_name)
+        except Exception as e:
+            error = getattr(e, "message", str(e))
+            if self.task:
+                self.task.increment_tools_errors()
+            if self.agent and self.agent.verbose:
+                self._printer.print(content=f"\n\n{error}\n", color="red")
+            return error
+
+        if (
+            isinstance(tool, CrewStructuredTool)
+            and tool.name == self._i18n.tools("add_image")["name"]  # type: ignore
+        ):
+            try:
+                return await self._ause(
+                    tool_string=tool_string, tool=tool, calling=calling
+                )
+            except Exception as e:
+                error = getattr(e, "message", str(e))
+                if self.task:
+                    self.task.increment_tools_errors()
+                if self.agent and self.agent.verbose:
+                    self._printer.print(content=f"\n\n{error}\n", color="red")
+                return error
+
+        return (
+            f"{await self._ause(tool_string=tool_string, tool=tool, calling=calling)}"
+        )
+
+    async def _ause(
+        self,
+        tool_string: str,
+        tool: CrewStructuredTool,
+        calling: ToolCalling | InstructorToolCalling,
+    ) -> str:
+        """Internal async tool execution implementation.
+
+        Args:
+            tool_string: The raw tool string from the agent.
+            tool: The tool to execute.
+            calling: The tool calling information.
+
+        Returns:
+            The result of the tool execution as a string.
+        """
+        if self._check_tool_repeated_usage(calling=calling):
+            try:
+                result = self._i18n.errors("task_repeated_usage").format(
+                    tool_names=self.tools_names
+                )
+                self._telemetry.tool_repeated_usage(
+                    llm=self.function_calling_llm,
+                    tool_name=tool.name,
+                    attempts=self._run_attempts,
+                )
+                return self._format_result(result=result)
+            except Exception:
+                if self.task:
+                    self.task.increment_tools_errors()
+
+        if self.agent:
+            event_data = {
+                "agent_key": self.agent.key,
+                "agent_role": self.agent.role,
+                "tool_name": self.action.tool,
+                "tool_args": self.action.tool_input,
+                "tool_class": self.action.tool,
+                "agent": self.agent,
+            }
+
+            if self.agent.fingerprint:  # type: ignore
+                event_data.update(self.agent.fingerprint)  # type: ignore
+            if self.task:
+                event_data["task_name"] = self.task.name or self.task.description
+                event_data["task_id"] = str(self.task.id)
+            crewai_event_bus.emit(self, ToolUsageStartedEvent(**event_data))
+
+        started_at = time.time()
+        from_cache = False
+        result = None  # type: ignore
+
+        if self.tools_handler and self.tools_handler.cache:
+            input_str = ""
+            if calling.arguments:
+                if isinstance(calling.arguments, dict):
+                    input_str = json.dumps(calling.arguments)
+                else:
+                    input_str = str(calling.arguments)
+
+            result = self.tools_handler.cache.read(
+                tool=calling.tool_name, input=input_str
+            )  # type: ignore
+            from_cache = result is not None
+
+        available_tool = next(
+            (
+                available_tool
+                for available_tool in self.tools
+                if available_tool.name == tool.name
+            ),
+            None,
+        )
+
+        usage_limit_error = self._check_usage_limit(available_tool, tool.name)
+        if usage_limit_error:
+            try:
+                result = usage_limit_error
+                self._telemetry.tool_usage_error(llm=self.function_calling_llm)
+                return self._format_result(result=result)
+            except Exception:
+                if self.task:
+                    self.task.increment_tools_errors()
+
+        if result is None:
+            try:
+                if calling.tool_name in [
+                    "Delegate work to coworker",
+                    "Ask question to coworker",
+                ]:
+                    coworker = (
+                        calling.arguments.get("coworker") if calling.arguments else None
+                    )
+                    if self.task:
+                        self.task.increment_delegations(coworker)
+
+                if calling.arguments:
+                    try:
+                        acceptable_args = tool.args_schema.model_json_schema()[
+                            "properties"
+                        ].keys()
+                        arguments = {
+                            k: v
+                            for k, v in calling.arguments.items()
+                            if k in acceptable_args
+                        }
+                        arguments = self._add_fingerprint_metadata(arguments)
+                        result = await tool.ainvoke(input=arguments)
+                    except Exception:
+                        arguments = calling.arguments
+                        arguments = self._add_fingerprint_metadata(arguments)
+                        result = await tool.ainvoke(input=arguments)
+                else:
+                    arguments = self._add_fingerprint_metadata({})
+                    result = await tool.ainvoke(input=arguments)
+            except Exception as e:
+                self.on_tool_error(tool=tool, tool_calling=calling, e=e)
+                self._run_attempts += 1
+                if self._run_attempts > self._max_parsing_attempts:
+                    self._telemetry.tool_usage_error(llm=self.function_calling_llm)
+                    error_message = self._i18n.errors("tool_usage_exception").format(
+                        error=e, tool=tool.name, tool_inputs=tool.description
+                    )
+                    error = ToolUsageError(
+                        f"\n{error_message}.\nMoving on then. {self._i18n.slice('format').format(tool_names=self.tools_names)}"
+                    ).message
+                    if self.task:
+                        self.task.increment_tools_errors()
+                    if self.agent and self.agent.verbose:
+                        self._printer.print(
+                            content=f"\n\n{error_message}\n", color="red"
+                        )
+                    return error
+
+                if self.task:
+                    self.task.increment_tools_errors()
+                return await self.ause(calling=calling, tool_string=tool_string)
+
+            if self.tools_handler:
+                should_cache = True
+                if (
+                    hasattr(available_tool, "cache_function")
+                    and available_tool.cache_function
+                ):
+                    should_cache = available_tool.cache_function(
+                        calling.arguments, result
+                    )
+
+                self.tools_handler.on_tool_use(
+                    calling=calling, output=result, should_cache=should_cache
+                )
+
+        self._telemetry.tool_usage(
+            llm=self.function_calling_llm,
+            tool_name=tool.name,
+            attempts=self._run_attempts,
+        )
+        result = self._format_result(result=result)
+        data = {
+            "result": result,
+            "tool_name": tool.name,
+            "tool_args": calling.arguments,
+        }
+
+        self.on_tool_use_finished(
+            tool=tool,
+            tool_calling=calling,
+            from_cache=from_cache,
+            started_at=started_at,
+            result=result,
+        )
+
+        if (
+            hasattr(available_tool, "result_as_answer")
+            and available_tool.result_as_answer  # type: ignore
+        ):
+            result_as_answer = available_tool.result_as_answer  # type: ignore
+            data["result_as_answer"] = result_as_answer  # type: ignore
+
+        if self.agent and hasattr(self.agent, "tools_results"):
+            self.agent.tools_results.append(data)
+
+        if available_tool and hasattr(available_tool, "current_usage_count"):
+            available_tool.current_usage_count += 1
+            if (
+                hasattr(available_tool, "max_usage_count")
+                and available_tool.max_usage_count is not None
+            ):
+                self._printer.print(
+                    content=f"Tool '{available_tool.name}' usage: {available_tool.current_usage_count}/{available_tool.max_usage_count}",
+                    color="blue",
+                )
+
+        return result
+
     def _use(
         self,
         tool_string: str,

lib/crewai/src/crewai/utilities/tool_utils.py

@@ -26,6 +26,138 @@ if TYPE_CHECKING:
     from crewai.task import Task
 
 
+async def aexecute_tool_and_check_finality(
+    agent_action: AgentAction,
+    tools: list[CrewStructuredTool],
+    i18n: I18N,
+    agent_key: str | None = None,
+    agent_role: str | None = None,
+    tools_handler: ToolsHandler | None = None,
+    task: Task | None = None,
+    agent: Agent | BaseAgent | None = None,
+    function_calling_llm: BaseLLM | LLM | None = None,
+    fingerprint_context: dict[str, str] | None = None,
+    crew: Crew | None = None,
+) -> ToolResult:
+    """Execute a tool asynchronously and check if the result should be a final answer.
+
+    This is the async version of execute_tool_and_check_finality. It integrates tool
+    hooks for before and after tool execution, allowing programmatic interception
+    and modification of tool calls.
+
+    Args:
+        agent_action: The action containing the tool to execute.
+        tools: List of available tools.
+        i18n: Internationalization settings.
+        agent_key: Optional key for event emission.
+        agent_role: Optional role for event emission.
+        tools_handler: Optional tools handler for tool execution.
+        task: Optional task for tool execution.
+        agent: Optional agent instance for tool execution.
+        function_calling_llm: Optional LLM for function calling.
+        fingerprint_context: Optional context for fingerprinting.
+        crew: Optional crew instance for hook context.
+
+    Returns:
+        ToolResult containing the execution result and whether it should be
+        treated as a final answer.
+    """
+    logger = Logger(verbose=crew.verbose if crew else False)
+    tool_name_to_tool_map = {tool.name: tool for tool in tools}
+
+    if agent_key and agent_role and agent:
+        fingerprint_context = fingerprint_context or {}
+        if agent:
+            if hasattr(agent, "set_fingerprint") and callable(agent.set_fingerprint):
+                if isinstance(fingerprint_context, dict):
+                    try:
+                        fingerprint_obj = Fingerprint.from_dict(fingerprint_context)
+                        agent.set_fingerprint(fingerprint=fingerprint_obj)
+                    except Exception as e:
+                        raise ValueError(f"Failed to set fingerprint: {e}") from e
+
+    tool_usage = ToolUsage(
+        tools_handler=tools_handler,
+        tools=tools,
+        function_calling_llm=function_calling_llm,  # type: ignore[arg-type]
+        task=task,
+        agent=agent,
+        action=agent_action,
+    )
+
+    tool_calling = tool_usage.parse_tool_calling(agent_action.text)
+
+    if isinstance(tool_calling, ToolUsageError):
+        return ToolResult(tool_calling.message, False)
+
+    if tool_calling.tool_name.casefold().strip() in [
+        name.casefold().strip() for name in tool_name_to_tool_map
+    ] or tool_calling.tool_name.casefold().replace("_", " ") in [
+        name.casefold().strip() for name in tool_name_to_tool_map
+    ]:
+        tool = tool_name_to_tool_map.get(tool_calling.tool_name)
+        if not tool:
+            tool_result = i18n.errors("wrong_tool_name").format(
+                tool=tool_calling.tool_name,
+                tools=", ".join([t.name.casefold() for t in tools]),
+            )
+            return ToolResult(result=tool_result, result_as_answer=False)
+
+        tool_input = tool_calling.arguments if tool_calling.arguments else {}
+        hook_context = ToolCallHookContext(
+            tool_name=tool_calling.tool_name,
+            tool_input=tool_input,
+            tool=tool,
+            agent=agent,
+            task=task,
+            crew=crew,
+        )
+
+        before_hooks = get_before_tool_call_hooks()
+        try:
+            for hook in before_hooks:
+                result = hook(hook_context)
+                if result is False:
+                    blocked_message = (
+                        f"Tool execution blocked by hook. "
+                        f"Tool: {tool_calling.tool_name}"
+                    )
+                    return ToolResult(blocked_message, False)
+        except Exception as e:
+            logger.log("error", f"Error in before_tool_call hook: {e}")
+
+        tool_result = await tool_usage.ause(tool_calling, agent_action.text)
+
+        after_hook_context = ToolCallHookContext(
+            tool_name=tool_calling.tool_name,
+            tool_input=tool_input,
+            tool=tool,
+            agent=agent,
+            task=task,
+            crew=crew,
+            tool_result=tool_result,
+        )
+
+        after_hooks = get_after_tool_call_hooks()
+        modified_result: str = tool_result
+        try:
+            for after_hook in after_hooks:
+                hook_result = after_hook(after_hook_context)
+                if hook_result is not None:
+                    modified_result = hook_result
+                    after_hook_context.tool_result = modified_result
+        except Exception as e:
+            logger.log("error", f"Error in after_tool_call hook: {e}")
+
+        return ToolResult(modified_result, tool.result_as_answer)
+
+    tool_result = i18n.errors("wrong_tool_name").format(
+        tool=tool_calling.tool_name,
+        tools=", ".join([tool.name.casefold() for tool in tools]),
+    )
+    return ToolResult(result=tool_result, result_as_answer=False)
+
+
 def execute_tool_and_check_finality(
     agent_action: AgentAction,
     tools: list[CrewStructuredTool],
@@ -141,10 +273,10 @@ def execute_tool_and_check_finality(
 
         # Execute after_tool_call hooks
         after_hooks = get_after_tool_call_hooks()
-        modified_result = tool_result
+        modified_result: str = tool_result
         try:
-            for hook in after_hooks:
-                hook_result = hook(after_hook_context)
+            for after_hook in after_hooks:
+                hook_result = after_hook(after_hook_context)
                 if hook_result is not None:
                     modified_result = hook_result
                     after_hook_context.tool_result = modified_result

lib/crewai/tests/tools/test_async_tools.py

@@ -0,0 +1,196 @@
+"""Tests for async tool functionality."""
+
+import asyncio
+
+import pytest
+
+from crewai.tools import BaseTool, tool
+
+
+class SyncTool(BaseTool):
+    """Test tool with synchronous _run method."""
+
+    name: str = "sync_tool"
+    description: str = "A synchronous tool for testing"
+
+    def _run(self, input_text: str) -> str:
+        """Process input text synchronously."""
+        return f"Sync processed: {input_text}"
+
+
+class AsyncTool(BaseTool):
+    """Test tool with both sync and async implementations."""
+
+    name: str = "async_tool"
+    description: str = "An asynchronous tool for testing"
+
+    def _run(self, input_text: str) -> str:
+        """Process input text synchronously."""
+        return f"Sync processed: {input_text}"
+
+    async def _arun(self, input_text: str) -> str:
+        """Process input text asynchronously."""
+        await asyncio.sleep(0.01)
+        return f"Async processed: {input_text}"
+
+
+class TestBaseTool:
+    """Tests for BaseTool async functionality."""
+
+    def test_sync_tool_run_returns_result(self) -> None:
+        """Test that sync tool run() returns correct result."""
+        tool = SyncTool()
+        result = tool.run(input_text="hello")
+        assert result == "Sync processed: hello"
+
+    def test_async_tool_run_returns_result(self) -> None:
+        """Test that async tool run() works."""
+        tool = AsyncTool()
+        result = tool.run(input_text="hello")
+        assert result == "Sync processed: hello"
+
+    @pytest.mark.asyncio
+    async def test_sync_tool_arun_raises_not_implemented(self) -> None:
+        """Test that sync tool arun() raises NotImplementedError."""
+        tool = SyncTool()
+        with pytest.raises(NotImplementedError):
+            await tool.arun(input_text="hello")
+
+    @pytest.mark.asyncio
+    async def test_async_tool_arun_returns_result(self) -> None:
+        """Test that async tool arun() awaits directly."""
+        tool = AsyncTool()
+        result = await tool.arun(input_text="hello")
+        assert result == "Async processed: hello"
+
+    @pytest.mark.asyncio
+    async def test_arun_increments_usage_count(self) -> None:
+        """Test that arun increments the usage count."""
+        tool = AsyncTool()
+        assert tool.current_usage_count == 0
+
+        await tool.arun(input_text="test")
+        assert tool.current_usage_count == 1
+
+        await tool.arun(input_text="test2")
+        assert tool.current_usage_count == 2
+
+    @pytest.mark.asyncio
+    async def test_multiple_async_tools_run_concurrently(self) -> None:
+        """Test that multiple async tools can run concurrently."""
+        tool1 = AsyncTool()
+        tool2 = AsyncTool()
+
+        results = await asyncio.gather(
+            tool1.arun(input_text="first"),
+            tool2.arun(input_text="second"),
+        )
+
+        assert results[0] == "Async processed: first"
+        assert results[1] == "Async processed: second"
+
+
+class TestToolDecorator:
+    """Tests for @tool decorator with async functions."""
+
+    def test_sync_decorated_tool_run(self) -> None:
+        """Test sync decorated tool works with run()."""
+
+        @tool("sync_decorated")
+        def sync_func(value: str) -> str:
+            """A sync decorated tool."""
+            return f"sync: {value}"
+
+        result = sync_func.run(value="test")
+        assert result == "sync: test"
+
+    def test_async_decorated_tool_run(self) -> None:
+        """Test async decorated tool works with run()."""
+
+        @tool("async_decorated")
+        async def async_func(value: str) -> str:
+            """An async decorated tool."""
+            await asyncio.sleep(0.01)
+            return f"async: {value}"
+
+        result = async_func.run(value="test")
+        assert result == "async: test"
+
+    @pytest.mark.asyncio
+    async def test_sync_decorated_tool_arun_raises(self) -> None:
+        """Test sync decorated tool arun() raises NotImplementedError."""
+
+        @tool("sync_decorated_arun")
+        def sync_func(value: str) -> str:
+            """A sync decorated tool."""
+            return f"sync: {value}"
+
+        with pytest.raises(NotImplementedError):
+            await sync_func.arun(value="test")
+
+    @pytest.mark.asyncio
+    async def test_async_decorated_tool_arun(self) -> None:
+        """Test async decorated tool works with arun()."""
+
+        @tool("async_decorated_arun")
+        async def async_func(value: str) -> str:
+            """An async decorated tool."""
+            await asyncio.sleep(0.01)
+            return f"async: {value}"
+
+        result = await async_func.arun(value="test")
+        assert result == "async: test"
+
+
+class TestAsyncToolWithIO:
+    """Tests for async tools with simulated I/O operations."""
+
+    @pytest.mark.asyncio
+    async def test_async_tool_simulated_io(self) -> None:
+        """Test async tool with simulated I/O delay."""
+
+        class SlowAsyncTool(BaseTool):
+            name: str = "slow_async"
+            description: str = "Simulates slow I/O"
+
+            def _run(self, delay: float) -> str:
+                return f"Completed after {delay}s"
+
+            async def _arun(self, delay: float) -> str:
+                await asyncio.sleep(delay)
+                return f"Completed after {delay}s"
+
+        tool = SlowAsyncTool()
+        result = await tool.arun(delay=0.05)
+        assert result == "Completed after 0.05s"
+
+    @pytest.mark.asyncio
+    async def test_multiple_slow_tools_concurrent(self) -> None:
+        """Test that slow async tools benefit from concurrency."""
+
+        class SlowAsyncTool(BaseTool):
+            name: str = "slow_async"
+            description: str = "Simulates slow I/O"
+
+            def _run(self, task_id: int, delay: float) -> str:
+                return f"Task {task_id} done"
+
+            async def _arun(self, task_id: int, delay: float) -> str:
+                await asyncio.sleep(delay)
+                return f"Task {task_id} done"
+
+        tool = SlowAsyncTool()
+
+        import time
+
+        start = time.time()
+        results = await asyncio.gather(
+            tool.arun(task_id=1, delay=0.1),
+            tool.arun(task_id=2, delay=0.1),
+            tool.arun(task_id=3, delay=0.1),
+        )
+        elapsed = time.time() - start
+
+        assert len(results) == 3
+        assert all("done" in r for r in results)
+        assert elapsed < 0.25, f"Expected concurrent execution, took {elapsed}s"