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MCP Servers

MCPServer

Bases: ABC

Base class for Model Context Protocol servers.

Source code in src/agents/mcp/server.py 
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class MCPServer(abc.ABC):
    """Base class for Model Context Protocol servers."""

    def __init__(
        self,
        use_structured_content: bool = False,
        require_approval: RequireApprovalSetting = None,
        failure_error_function: ToolErrorFunction | None | _UnsetType = _UNSET,
    ):
        """
        Args:
            use_structured_content: Whether to use `tool_result.structured_content` when calling an
                MCP tool.Defaults to False for backwards compatibility - most MCP servers still
                include the structured content in the `tool_result.content`, and using it by
                default will cause duplicate content. You can set this to True if you know the
                server will not duplicate the structured content in the `tool_result.content`.
            require_approval: Approval policy for tools on this server. Accepts "always"/"never",
                a dict of tool names to those values, a boolean, or an object with always/never
                tool lists (mirroring TS requireApproval). Normalized into a needs_approval policy.
            failure_error_function: Optional function used to convert MCP tool failures into
                a model-visible error message. If explicitly set to None, tool errors will be
                raised instead of converted. If left unset, the agent-level configuration (or
                SDK default) will be used.
        """
        self.use_structured_content = use_structured_content
        self._needs_approval_policy = self._normalize_needs_approval(
            require_approval=require_approval
        )
        self._failure_error_function = failure_error_function

    @abc.abstractmethod
    async def connect(self):
        """Connect to the server. For example, this might mean spawning a subprocess or
        opening a network connection. The server is expected to remain connected until
        `cleanup()` is called.
        """
        pass

    @property
    @abc.abstractmethod
    def name(self) -> str:
        """A readable name for the server."""
        pass

    @abc.abstractmethod
    async def cleanup(self):
        """Cleanup the server. For example, this might mean closing a subprocess or
        closing a network connection.
        """
        pass

    @abc.abstractmethod
    async def list_tools(
        self,
        run_context: RunContextWrapper[Any] | None = None,
        agent: AgentBase | None = None,
    ) -> list[MCPTool]:
        """List the tools available on the server."""
        pass

    @abc.abstractmethod
    async def call_tool(self, tool_name: str, arguments: dict[str, Any] | None) -> CallToolResult:
        """Invoke a tool on the server."""
        pass

    @abc.abstractmethod
    async def list_prompts(
        self,
    ) -> ListPromptsResult:
        """List the prompts available on the server."""
        pass

    @abc.abstractmethod
    async def get_prompt(
        self, name: str, arguments: dict[str, Any] | None = None
    ) -> GetPromptResult:
        """Get a specific prompt from the server."""
        pass

    @staticmethod
    def _normalize_needs_approval(
        *,
        require_approval: RequireApprovalSetting,
    ) -> (
        bool
        | dict[str, bool]
        | Callable[[RunContextWrapper[Any], AgentBase, MCPTool], MaybeAwaitable[bool]]
    ):
        """Normalize approval inputs to booleans or a name->bool map."""

        if require_approval is None:
            return False

        def _to_bool(value: str) -> bool:
            return value == "always"

        def _is_tool_list_schema(value: object) -> bool:
            if not isinstance(value, dict):
                return False
            for key in ("always", "never"):
                if key not in value:
                    continue
                entry = value.get(key)
                if isinstance(entry, dict) and "tool_names" in entry:
                    return True
            return False

        if isinstance(require_approval, dict) and _is_tool_list_schema(require_approval):
            always_entry: RequireApprovalToolList | Any = require_approval.get("always", {})
            never_entry: RequireApprovalToolList | Any = require_approval.get("never", {})
            always_names = (
                always_entry.get("tool_names", []) if isinstance(always_entry, dict) else []
            )
            never_names = never_entry.get("tool_names", []) if isinstance(never_entry, dict) else []
            tool_list_mapping: dict[str, bool] = {}
            for name in always_names:
                tool_list_mapping[str(name)] = True
            for name in never_names:
                tool_list_mapping[str(name)] = False
            return tool_list_mapping

        if isinstance(require_approval, dict):
            tool_mapping: dict[str, bool] = {}
            for name, value in require_approval.items():
                if isinstance(value, bool):
                    tool_mapping[str(name)] = value
                elif isinstance(value, str) and value in ("always", "never"):
                    tool_mapping[str(name)] = _to_bool(value)
            return tool_mapping

        if isinstance(require_approval, bool):
            return require_approval

        return _to_bool(require_approval)

    def _get_needs_approval_for_tool(
        self,
        tool: MCPTool,
        agent: AgentBase,
    ) -> bool | Callable[[RunContextWrapper[Any], dict[str, Any], str], Awaitable[bool]]:
        """Return a FunctionTool.needs_approval value for a given MCP tool."""

        policy = self._needs_approval_policy

        if callable(policy):

            async def _needs_approval(
                run_context: RunContextWrapper[Any], _args: dict[str, Any], _call_id: str
            ) -> bool:
                result = policy(run_context, agent, tool)
                if inspect.isawaitable(result):
                    result = await result
                return bool(result)

            return _needs_approval

        if isinstance(policy, dict):
            return bool(policy.get(tool.name, False))

        return bool(policy)

    def _get_failure_error_function(
        self, agent_failure_error_function: ToolErrorFunction | None
    ) -> ToolErrorFunction | None:
        """Return the effective error handler for MCP tool failures."""
        if self._failure_error_function is _UNSET:
            return agent_failure_error_function
        return cast(ToolErrorFunction | None, self._failure_error_function)

name abstractmethod property 

name: str

A readable name for the server.

__init__ 

__init__(
    use_structured_content: bool = False,
    require_approval: RequireApprovalSetting = None,
    failure_error_function: ToolErrorFunction
    | None
    | _UnsetType = _UNSET,
)

Parameters:

Name Type Description Default
use_structured_content bool

Whether to use tool_result.structured_content when calling an MCP tool.Defaults to False for backwards compatibility - most MCP servers still include the structured content in the tool_result.content, and using it by default will cause duplicate content. You can set this to True if you know the server will not duplicate the structured content in the tool_result.content.

 False
require_approval RequireApprovalSetting

Approval policy for tools on this server. Accepts "always"/"never", a dict of tool names to those values, a boolean, or an object with always/never tool lists (mirroring TS requireApproval). Normalized into a needs_approval policy.

 None
failure_error_function ToolErrorFunction | None | _UnsetType

Optional function used to convert MCP tool failures into a model-visible error message. If explicitly set to None, tool errors will be raised instead of converted. If left unset, the agent-level configuration (or SDK default) will be used.

 _UNSET
Source code in src/agents/mcp/server.py 
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def __init__(
    self,
    use_structured_content: bool = False,
    require_approval: RequireApprovalSetting = None,
    failure_error_function: ToolErrorFunction | None | _UnsetType = _UNSET,
):
    """
    Args:
        use_structured_content: Whether to use `tool_result.structured_content` when calling an
            MCP tool.Defaults to False for backwards compatibility - most MCP servers still
            include the structured content in the `tool_result.content`, and using it by
            default will cause duplicate content. You can set this to True if you know the
            server will not duplicate the structured content in the `tool_result.content`.
        require_approval: Approval policy for tools on this server. Accepts "always"/"never",
            a dict of tool names to those values, a boolean, or an object with always/never
            tool lists (mirroring TS requireApproval). Normalized into a needs_approval policy.
        failure_error_function: Optional function used to convert MCP tool failures into
            a model-visible error message. If explicitly set to None, tool errors will be
            raised instead of converted. If left unset, the agent-level configuration (or
            SDK default) will be used.
    """
    self.use_structured_content = use_structured_content
    self._needs_approval_policy = self._normalize_needs_approval(
        require_approval=require_approval
    )
    self._failure_error_function = failure_error_function

connect abstractmethod async 

connect()

Connect to the server. For example, this might mean spawning a subprocess or opening a network connection. The server is expected to remain connected until cleanup() is called.

Source code in src/agents/mcp/server.py 
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@abc.abstractmethod
async def connect(self):
    """Connect to the server. For example, this might mean spawning a subprocess or
    opening a network connection. The server is expected to remain connected until
    `cleanup()` is called.
    """
    pass

cleanup abstractmethod async 

cleanup()

Cleanup the server. For example, this might mean closing a subprocess or closing a network connection.

Source code in src/agents/mcp/server.py 
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@abc.abstractmethod
async def cleanup(self):
    """Cleanup the server. For example, this might mean closing a subprocess or
    closing a network connection.
    """
    pass

list_tools abstractmethod async 

list_tools(
    run_context: RunContextWrapper[Any] | None = None,
    agent: AgentBase | None = None,
) -> list[Tool]

List the tools available on the server.

Source code in src/agents/mcp/server.py 
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@abc.abstractmethod
async def list_tools(
    self,
    run_context: RunContextWrapper[Any] | None = None,
    agent: AgentBase | None = None,
) -> list[MCPTool]:
    """List the tools available on the server."""
    pass

call_tool abstractmethod async 

call_tool(
    tool_name: str, arguments: dict[str, Any] | None
) -> CallToolResult

Invoke a tool on the server.

Source code in src/agents/mcp/server.py 
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@abc.abstractmethod
async def call_tool(self, tool_name: str, arguments: dict[str, Any] | None) -> CallToolResult:
    """Invoke a tool on the server."""
    pass

list_prompts abstractmethod async 

list_prompts() -> ListPromptsResult

List the prompts available on the server.

Source code in src/agents/mcp/server.py 
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@abc.abstractmethod
async def list_prompts(
    self,
) -> ListPromptsResult:
    """List the prompts available on the server."""
    pass

get_prompt abstractmethod async 

get_prompt(
    name: str, arguments: dict[str, Any] | None = None
) -> GetPromptResult

Get a specific prompt from the server.

Source code in src/agents/mcp/server.py 
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@abc.abstractmethod
async def get_prompt(
    self, name: str, arguments: dict[str, Any] | None = None
) -> GetPromptResult:
    """Get a specific prompt from the server."""
    pass

MCPServerStdioParams

Bases: TypedDict

Mirrors mcp.client.stdio.StdioServerParameters, but lets you pass params without another import.

Source code in src/agents/mcp/server.py 
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class MCPServerStdioParams(TypedDict):
    """Mirrors `mcp.client.stdio.StdioServerParameters`, but lets you pass params without another
    import.
    """

    command: str
    """The executable to run to start the server. For example, `python` or `node`."""

    args: NotRequired[list[str]]
    """Command line args to pass to the `command` executable. For example, `['foo.py']` or
    `['server.js', '--port', '8080']`."""

    env: NotRequired[dict[str, str]]
    """The environment variables to set for the server. ."""

    cwd: NotRequired[str | Path]
    """The working directory to use when spawning the process."""

    encoding: NotRequired[str]
    """The text encoding used when sending/receiving messages to the server. Defaults to `utf-8`."""

    encoding_error_handler: NotRequired[Literal["strict", "ignore", "replace"]]
    """The text encoding error handler. Defaults to `strict`.

    See https://docs.python.org/3/library/codecs.html#codec-base-classes for
    explanations of possible values.
    """

command instance-attribute 

command: str

The executable to run to start the server. For example, python or node.

args instance-attribute 

args: NotRequired[list[str]]

Command line args to pass to the command executable. For example, ['foo.py'] or ['server.js', '--port', '8080'].

env instance-attribute 

env: NotRequired[dict[str, str]]

The environment variables to set for the server. .

cwd instance-attribute 

cwd: NotRequired[str | Path]

The working directory to use when spawning the process.

encoding instance-attribute 

encoding: NotRequired[str]

The text encoding used when sending/receiving messages to the server. Defaults to utf-8.

encoding_error_handler instance-attribute 

encoding_error_handler: NotRequired[
    Literal["strict", "ignore", "replace"]
]

The text encoding error handler. Defaults to strict.

See https://docs.python.org/3/library/codecs.html#codec-base-classes for explanations of possible values.

MCPServerStdio

Bases: _MCPServerWithClientSession

MCP server implementation that uses the stdio transport. See the [spec] (https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/transports/#stdio) for details.

Source code in src/agents/mcp/server.py 
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class MCPServerStdio(_MCPServerWithClientSession):
    """MCP server implementation that uses the stdio transport. See the [spec]
    (https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/transports/#stdio) for
    details.
    """

    def __init__(
        self,
        params: MCPServerStdioParams,
        cache_tools_list: bool = False,
        name: str | None = None,
        client_session_timeout_seconds: float | None = 5,
        tool_filter: ToolFilter = None,
        use_structured_content: bool = False,
        max_retry_attempts: int = 0,
        retry_backoff_seconds_base: float = 1.0,
        message_handler: MessageHandlerFnT | None = None,
        require_approval: RequireApprovalSetting = None,
        failure_error_function: ToolErrorFunction | None | _UnsetType = _UNSET,
    ):
        """Create a new MCP server based on the stdio transport.

        Args:
            params: The params that configure the server. This includes the command to run to
                start the server, the args to pass to the command, the environment variables to
                set for the server, the working directory to use when spawning the process, and
                the text encoding used when sending/receiving messages to the server.
            cache_tools_list: Whether to cache the tools list. If `True`, the tools list will be
                cached and only fetched from the server once. If `False`, the tools list will be
                fetched from the server on each call to `list_tools()`. The cache can be
                invalidated by calling `invalidate_tools_cache()`. You should set this to `True`
                if you know the server will not change its tools list, because it can drastically
                improve latency (by avoiding a round-trip to the server every time).
            name: A readable name for the server. If not provided, we'll create one from the
                command.
            client_session_timeout_seconds: the read timeout passed to the MCP ClientSession.
            tool_filter: The tool filter to use for filtering tools.
            use_structured_content: Whether to use `tool_result.structured_content` when calling an
                MCP tool. Defaults to False for backwards compatibility - most MCP servers still
                include the structured content in the `tool_result.content`, and using it by
                default will cause duplicate content. You can set this to True if you know the
                server will not duplicate the structured content in the `tool_result.content`.
            max_retry_attempts: Number of times to retry failed list_tools/call_tool calls.
                Defaults to no retries.
            retry_backoff_seconds_base: The base delay, in seconds, for exponential
                backoff between retries.
            message_handler: Optional handler invoked for session messages as delivered by the
                ClientSession.
            require_approval: Approval policy for tools on this server. Accepts "always"/"never",
                a dict of tool names to those values, or an object with always/never tool lists.
            failure_error_function: Optional function used to convert MCP tool failures into
                a model-visible error message. If explicitly set to None, tool errors will be
                raised instead of converted. If left unset, the agent-level configuration (or
                SDK default) will be used.
        """
        super().__init__(
            cache_tools_list,
            client_session_timeout_seconds,
            tool_filter,
            use_structured_content,
            max_retry_attempts,
            retry_backoff_seconds_base,
            message_handler=message_handler,
            require_approval=require_approval,
            failure_error_function=failure_error_function,
        )

        self.params = StdioServerParameters(
            command=params["command"],
            args=params.get("args", []),
            env=params.get("env"),
            cwd=params.get("cwd"),
            encoding=params.get("encoding", "utf-8"),
            encoding_error_handler=params.get("encoding_error_handler", "strict"),
        )

        self._name = name or f"stdio: {self.params.command}"

    def create_streams(
        self,
    ) -> AbstractAsyncContextManager[
        tuple[
            MemoryObjectReceiveStream[SessionMessage | Exception],
            MemoryObjectSendStream[SessionMessage],
            GetSessionIdCallback | None,
        ]
    ]:
        """Create the streams for the server."""
        return stdio_client(self.params)

    @property
    def name(self) -> str:
        """A readable name for the server."""
        return self._name

name property 

name: str

A readable name for the server.

__init__ 

__init__(
    params: MCPServerStdioParams,
    cache_tools_list: bool = False,
    name: str | None = None,
    client_session_timeout_seconds: float | None = 5,
    tool_filter: ToolFilter = None,
    use_structured_content: bool = False,
    max_retry_attempts: int = 0,
    retry_backoff_seconds_base: float = 1.0,
    message_handler: MessageHandlerFnT | None = None,
    require_approval: RequireApprovalSetting = None,
    failure_error_function: ToolErrorFunction
    | None
    | _UnsetType = _UNSET,
)

Create a new MCP server based on the stdio transport.

Parameters:

Name Type Description Default
params MCPServerStdioParams

The params that configure the server. This includes the command to run to start the server, the args to pass to the command, the environment variables to set for the server, the working directory to use when spawning the process, and the text encoding used when sending/receiving messages to the server.

 required
cache_tools_list bool

Whether to cache the tools list. If True, the tools list will be cached and only fetched from the server once. If False, the tools list will be fetched from the server on each call to list_tools(). The cache can be invalidated by calling invalidate_tools_cache(). You should set this to True if you know the server will not change its tools list, because it can drastically improve latency (by avoiding a round-trip to the server every time).

 False
name str | None

A readable name for the server. If not provided, we'll create one from the command.

 None
client_session_timeout_seconds float | None

the read timeout passed to the MCP ClientSession.

 5
tool_filter ToolFilter

The tool filter to use for filtering tools.

 None
use_structured_content bool

Whether to use tool_result.structured_content when calling an MCP tool. Defaults to False for backwards compatibility - most MCP servers still include the structured content in the tool_result.content, and using it by default will cause duplicate content. You can set this to True if you know the server will not duplicate the structured content in the tool_result.content.

 False
max_retry_attempts int

Number of times to retry failed list_tools/call_tool calls. Defaults to no retries.

 0
retry_backoff_seconds_base float

The base delay, in seconds, for exponential backoff between retries.

 1.0
message_handler MessageHandlerFnT | None

Optional handler invoked for session messages as delivered by the ClientSession.

 None
require_approval RequireApprovalSetting

Approval policy for tools on this server. Accepts "always"/"never", a dict of tool names to those values, or an object with always/never tool lists.

 None
failure_error_function ToolErrorFunction | None | _UnsetType

Optional function used to convert MCP tool failures into a model-visible error message. If explicitly set to None, tool errors will be raised instead of converted. If left unset, the agent-level configuration (or SDK default) will be used.

 _UNSET
Source code in src/agents/mcp/server.py 
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def __init__(
    self,
    params: MCPServerStdioParams,
    cache_tools_list: bool = False,
    name: str | None = None,
    client_session_timeout_seconds: float | None = 5,
    tool_filter: ToolFilter = None,
    use_structured_content: bool = False,
    max_retry_attempts: int = 0,
    retry_backoff_seconds_base: float = 1.0,
    message_handler: MessageHandlerFnT | None = None,
    require_approval: RequireApprovalSetting = None,
    failure_error_function: ToolErrorFunction | None | _UnsetType = _UNSET,
):
    """Create a new MCP server based on the stdio transport.

    Args:
        params: The params that configure the server. This includes the command to run to
            start the server, the args to pass to the command, the environment variables to
            set for the server, the working directory to use when spawning the process, and
            the text encoding used when sending/receiving messages to the server.
        cache_tools_list: Whether to cache the tools list. If `True`, the tools list will be
            cached and only fetched from the server once. If `False`, the tools list will be
            fetched from the server on each call to `list_tools()`. The cache can be
            invalidated by calling `invalidate_tools_cache()`. You should set this to `True`
            if you know the server will not change its tools list, because it can drastically
            improve latency (by avoiding a round-trip to the server every time).
        name: A readable name for the server. If not provided, we'll create one from the
            command.
        client_session_timeout_seconds: the read timeout passed to the MCP ClientSession.
        tool_filter: The tool filter to use for filtering tools.
        use_structured_content: Whether to use `tool_result.structured_content` when calling an
            MCP tool. Defaults to False for backwards compatibility - most MCP servers still
            include the structured content in the `tool_result.content`, and using it by
            default will cause duplicate content. You can set this to True if you know the
            server will not duplicate the structured content in the `tool_result.content`.
        max_retry_attempts: Number of times to retry failed list_tools/call_tool calls.
            Defaults to no retries.
        retry_backoff_seconds_base: The base delay, in seconds, for exponential
            backoff between retries.
        message_handler: Optional handler invoked for session messages as delivered by the
            ClientSession.
        require_approval: Approval policy for tools on this server. Accepts "always"/"never",
            a dict of tool names to those values, or an object with always/never tool lists.
        failure_error_function: Optional function used to convert MCP tool failures into
            a model-visible error message. If explicitly set to None, tool errors will be
            raised instead of converted. If left unset, the agent-level configuration (or
            SDK default) will be used.
    """
    super().__init__(
        cache_tools_list,
        client_session_timeout_seconds,
        tool_filter,
        use_structured_content,
        max_retry_attempts,
        retry_backoff_seconds_base,
        message_handler=message_handler,
        require_approval=require_approval,
        failure_error_function=failure_error_function,
    )

    self.params = StdioServerParameters(
        command=params["command"],
        args=params.get("args", []),
        env=params.get("env"),
        cwd=params.get("cwd"),
        encoding=params.get("encoding", "utf-8"),
        encoding_error_handler=params.get("encoding_error_handler", "strict"),
    )

    self._name = name or f"stdio: {self.params.command}"

create_streams 

create_streams() -> AbstractAsyncContextManager[
    tuple[
        MemoryObjectReceiveStream[
            SessionMessage | Exception
        ],
        MemoryObjectSendStream[SessionMessage],
        GetSessionIdCallback | None,
    ]
]

Create the streams for the server.

Source code in src/agents/mcp/server.py 
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def create_streams(
    self,
) -> AbstractAsyncContextManager[
    tuple[
        MemoryObjectReceiveStream[SessionMessage | Exception],
        MemoryObjectSendStream[SessionMessage],
        GetSessionIdCallback | None,
    ]
]:
    """Create the streams for the server."""
    return stdio_client(self.params)

connect async 

connect()

Connect to the server.

Source code in src/agents/mcp/server.py 
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async def connect(self):
    """Connect to the server."""
    connection_succeeded = False
    try:
        transport = await self.exit_stack.enter_async_context(self.create_streams())
        # streamablehttp_client returns (read, write, get_session_id)
        # sse_client returns (read, write)

        read, write, *_ = transport

        session = await self.exit_stack.enter_async_context(
            ClientSession(
                read,
                write,
                timedelta(seconds=self.client_session_timeout_seconds)
                if self.client_session_timeout_seconds
                else None,
                message_handler=self.message_handler,
            )
        )
        server_result = await session.initialize()
        self.server_initialize_result = server_result
        self.session = session
        connection_succeeded = True
    except Exception as e:
        # Try to extract HTTP error from exception or ExceptionGroup
        http_error = self._extract_http_error_from_exception(e)
        if http_error:
            self._raise_user_error_for_http_error(http_error)

        # For CancelledError, preserve cancellation semantics - don't wrap it.
        # If it's masking an HTTP error, cleanup() will extract and raise UserError.
        if isinstance(e, asyncio.CancelledError):
            raise

        # For HTTP-related errors, wrap them
        if isinstance(e, (httpx.HTTPStatusError, httpx.ConnectError, httpx.TimeoutException)):
            self._raise_user_error_for_http_error(e)

        # For other errors, re-raise as-is (don't wrap non-HTTP errors)
        raise
    finally:
        # Always attempt cleanup on error, but suppress cleanup errors that mask the original
        if not connection_succeeded:
            try:
                await self.cleanup()
            except UserError:
                # Re-raise UserError from cleanup (contains the real HTTP error)
                raise
            except Exception as cleanup_error:
                # Suppress RuntimeError about cancel scopes during cleanup - this is a known
                # issue with the MCP library's async generator cleanup and shouldn't mask the
                # original error
                if isinstance(cleanup_error, RuntimeError) and "cancel scope" in str(
                    cleanup_error
                ):
                    logger.debug(
                        f"Ignoring cancel scope error during cleanup of MCP server "
                        f"'{self.name}': {cleanup_error}"
                    )
                else:
                    # Log other cleanup errors but don't raise - original error is more
                    # important
                    logger.warning(
                        f"Error during cleanup of MCP server '{self.name}': {cleanup_error}"
                    )

cleanup async 

cleanup()

Cleanup the server.

Source code in src/agents/mcp/server.py 
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async def cleanup(self):
    """Cleanup the server."""
    async with self._cleanup_lock:
        # Only raise HTTP errors if we're cleaning up after a failed connection.
        # During normal teardown (via __aexit__), log but don't raise to avoid
        # masking the original exception.
        is_failed_connection_cleanup = self.session is None

        try:
            await self.exit_stack.aclose()
        except asyncio.CancelledError as e:
            logger.debug(f"Cleanup cancelled for MCP server '{self.name}': {e}")
            raise
        except BaseExceptionGroup as eg:
            # Extract HTTP errors from ExceptionGroup raised during cleanup
            # This happens when background tasks fail (e.g., HTTP errors)
            http_error = None
            connect_error = None
            timeout_error = None
            error_message = f"Failed to connect to MCP server '{self.name}': "

            for exc in eg.exceptions:
                if isinstance(exc, httpx.HTTPStatusError):
                    http_error = exc
                elif isinstance(exc, httpx.ConnectError):
                    connect_error = exc
                elif isinstance(exc, httpx.TimeoutException):
                    timeout_error = exc

            # Only raise HTTP errors if we're cleaning up after a failed connection.
            # During normal teardown, log them instead.
            if http_error:
                if is_failed_connection_cleanup:
                    error_message += f"HTTP error {http_error.response.status_code} ({http_error.response.reason_phrase})"  # noqa: E501
                    raise UserError(error_message) from http_error
                else:
                    # Normal teardown - log but don't raise
                    logger.warning(
                        f"HTTP error during cleanup of MCP server '{self.name}': {http_error}"
                    )
            elif connect_error:
                if is_failed_connection_cleanup:
                    error_message += "Could not reach the server."
                    raise UserError(error_message) from connect_error
                else:
                    logger.warning(
                        f"Connection error during cleanup of MCP server '{self.name}': {connect_error}"  # noqa: E501
                    )
            elif timeout_error:
                if is_failed_connection_cleanup:
                    error_message += "Connection timeout."
                    raise UserError(error_message) from timeout_error
                else:
                    logger.warning(
                        f"Timeout error during cleanup of MCP server '{self.name}': {timeout_error}"  # noqa: E501
                    )
            else:
                # No HTTP error found, suppress RuntimeError about cancel scopes
                has_cancel_scope_error = any(
                    isinstance(exc, RuntimeError) and "cancel scope" in str(exc)
                    for exc in eg.exceptions
                )
                if has_cancel_scope_error:
                    logger.debug(f"Ignoring cancel scope error during cleanup: {eg}")
                else:
                    logger.error(f"Error cleaning up server: {eg}")
        except Exception as e:
            # Suppress RuntimeError about cancel scopes - this is a known issue with the MCP
            # library when background tasks fail during async generator cleanup
            if isinstance(e, RuntimeError) and "cancel scope" in str(e):
                logger.debug(f"Ignoring cancel scope error during cleanup: {e}")
            else:
                logger.error(f"Error cleaning up server: {e}")
        finally:
            self.session = None

list_tools async 

list_tools(
    run_context: RunContextWrapper[Any] | None = None,
    agent: AgentBase | None = None,
) -> list[Tool]

List the tools available on the server.

Source code in src/agents/mcp/server.py 
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async def list_tools(
    self,
    run_context: RunContextWrapper[Any] | None = None,
    agent: AgentBase | None = None,
) -> list[MCPTool]:
    """List the tools available on the server."""
    if not self.session:
        raise UserError("Server not initialized. Make sure you call `connect()` first.")
    session = self.session
    assert session is not None

    try:
        # Return from cache if caching is enabled, we have tools, and the cache is not dirty
        if self.cache_tools_list and not self._cache_dirty and self._tools_list:
            tools = self._tools_list
        else:
            # Fetch the tools from the server
            result = await self._run_with_retries(lambda: session.list_tools())
            self._tools_list = result.tools
            self._cache_dirty = False
            tools = self._tools_list

        # Filter tools based on tool_filter
        filtered_tools = tools
        if self.tool_filter is not None:
            filtered_tools = await self._apply_tool_filter(filtered_tools, run_context, agent)
        return filtered_tools
    except httpx.HTTPStatusError as e:
        status_code = e.response.status_code
        raise UserError(
            f"Failed to list tools from MCP server '{self.name}': HTTP error {status_code}"
        ) from e
    except httpx.ConnectError as e:
        raise UserError(
            f"Failed to list tools from MCP server '{self.name}': Connection lost. "
            f"The server may have disconnected."
        ) from e

call_tool async 

call_tool(
    tool_name: str, arguments: dict[str, Any] | None
) -> CallToolResult

Invoke a tool on the server.

Source code in src/agents/mcp/server.py 
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async def call_tool(self, tool_name: str, arguments: dict[str, Any] | None) -> CallToolResult:
    """Invoke a tool on the server."""
    if not self.session:
        raise UserError("Server not initialized. Make sure you call `connect()` first.")
    session = self.session
    assert session is not None

    try:
        return await self._run_with_retries(lambda: session.call_tool(tool_name, arguments))
    except httpx.HTTPStatusError as e:
        status_code = e.response.status_code
        raise UserError(
            f"Failed to call tool '{tool_name}' on MCP server '{self.name}': "
            f"HTTP error {status_code}"
        ) from e
    except httpx.ConnectError as e:
        raise UserError(
            f"Failed to call tool '{tool_name}' on MCP server '{self.name}': Connection lost. "
            f"The server may have disconnected."
        ) from e

list_prompts async 

list_prompts() -> ListPromptsResult

List the prompts available on the server.

Source code in src/agents/mcp/server.py 
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async def list_prompts(
    self,
) -> ListPromptsResult:
    """List the prompts available on the server."""
    if not self.session:
        raise UserError("Server not initialized. Make sure you call `connect()` first.")

    return await self.session.list_prompts()

get_prompt async 

get_prompt(
    name: str, arguments: dict[str, Any] | None = None
) -> GetPromptResult

Get a specific prompt from the server.

Source code in src/agents/mcp/server.py 
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async def get_prompt(
    self, name: str, arguments: dict[str, Any] | None = None
) -> GetPromptResult:
    """Get a specific prompt from the server."""
    if not self.session:
        raise UserError("Server not initialized. Make sure you call `connect()` first.")

    return await self.session.get_prompt(name, arguments)

invalidate_tools_cache 

invalidate_tools_cache()

Invalidate the tools cache.

Source code in src/agents/mcp/server.py 
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def invalidate_tools_cache(self):
    """Invalidate the tools cache."""
    self._cache_dirty = True

MCPServerSseParams

Bases: TypedDict

Mirrors the params inmcp.client.sse.sse_client.

Source code in src/agents/mcp/server.py 
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class MCPServerSseParams(TypedDict):
    """Mirrors the params in`mcp.client.sse.sse_client`."""

    url: str
    """The URL of the server."""

    headers: NotRequired[dict[str, str]]
    """The headers to send to the server."""

    timeout: NotRequired[float]
    """The timeout for the HTTP request. Defaults to 5 seconds."""

    sse_read_timeout: NotRequired[float]
    """The timeout for the SSE connection, in seconds. Defaults to 5 minutes."""

url instance-attribute 

url: str

The URL of the server.

headers instance-attribute 

headers: NotRequired[dict[str, str]]

The headers to send to the server.

timeout instance-attribute 

timeout: NotRequired[float]

The timeout for the HTTP request. Defaults to 5 seconds.

sse_read_timeout instance-attribute 

sse_read_timeout: NotRequired[float]

The timeout for the SSE connection, in seconds. Defaults to 5 minutes.

MCPServerSse

Bases: _MCPServerWithClientSession

MCP server implementation that uses the HTTP with SSE transport. See the [spec] (https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/transports/#http-with-sse) for details.

Source code in src/agents/mcp/server.py 
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class MCPServerSse(_MCPServerWithClientSession):
    """MCP server implementation that uses the HTTP with SSE transport. See the [spec]
    (https://spec.modelcontextprotocol.io/specification/2024-11-05/basic/transports/#http-with-sse)
    for details.
    """

    def __init__(
        self,
        params: MCPServerSseParams,
        cache_tools_list: bool = False,
        name: str | None = None,
        client_session_timeout_seconds: float | None = 5,
        tool_filter: ToolFilter = None,
        use_structured_content: bool = False,
        max_retry_attempts: int = 0,
        retry_backoff_seconds_base: float = 1.0,
        message_handler: MessageHandlerFnT | None = None,
        require_approval: RequireApprovalSetting = None,
        failure_error_function: ToolErrorFunction | None | _UnsetType = _UNSET,
    ):
        """Create a new MCP server based on the HTTP with SSE transport.

        Args:
            params: The params that configure the server. This includes the URL of the server,
                the headers to send to the server, the timeout for the HTTP request, and the
                timeout for the SSE connection.

            cache_tools_list: Whether to cache the tools list. If `True`, the tools list will be
                cached and only fetched from the server once. If `False`, the tools list will be
                fetched from the server on each call to `list_tools()`. The cache can be
                invalidated by calling `invalidate_tools_cache()`. You should set this to `True`
                if you know the server will not change its tools list, because it can drastically
                improve latency (by avoiding a round-trip to the server every time).

            name: A readable name for the server. If not provided, we'll create one from the
                URL.

            client_session_timeout_seconds: the read timeout passed to the MCP ClientSession.
            tool_filter: The tool filter to use for filtering tools.
            use_structured_content: Whether to use `tool_result.structured_content` when calling an
                MCP tool. Defaults to False for backwards compatibility - most MCP servers still
                include the structured content in the `tool_result.content`, and using it by
                default will cause duplicate content. You can set this to True if you know the
                server will not duplicate the structured content in the `tool_result.content`.
            max_retry_attempts: Number of times to retry failed list_tools/call_tool calls.
                Defaults to no retries.
            retry_backoff_seconds_base: The base delay, in seconds, for exponential
                backoff between retries.
            message_handler: Optional handler invoked for session messages as delivered by the
                ClientSession.
            require_approval: Approval policy for tools on this server. Accepts "always"/"never",
                a dict of tool names to those values, or an object with always/never tool lists.
            failure_error_function: Optional function used to convert MCP tool failures into
                a model-visible error message. If explicitly set to None, tool errors will be
                raised instead of converted. If left unset, the agent-level configuration (or
                SDK default) will be used.
        """
        super().__init__(
            cache_tools_list,
            client_session_timeout_seconds,
            tool_filter,
            use_structured_content,
            max_retry_attempts,
            retry_backoff_seconds_base,
            message_handler=message_handler,
            require_approval=require_approval,
            failure_error_function=failure_error_function,
        )

        self.params = params
        self._name = name or f"sse: {self.params['url']}"

    def create_streams(
        self,
    ) -> AbstractAsyncContextManager[
        tuple[
            MemoryObjectReceiveStream[SessionMessage | Exception],
            MemoryObjectSendStream[SessionMessage],
            GetSessionIdCallback | None,
        ]
    ]:
        """Create the streams for the server."""
        return sse_client(
            url=self.params["url"],
            headers=self.params.get("headers", None),
            timeout=self.params.get("timeout", 5),
            sse_read_timeout=self.params.get("sse_read_timeout", 60 * 5),
        )

    @property
    def name(self) -> str:
        """A readable name for the server."""
        return self._name

name property 

name: str

A readable name for the server.

__init__ 

__init__(
    params: MCPServerSseParams,
    cache_tools_list: bool = False,
    name: str | None = None,
    client_session_timeout_seconds: float | None = 5,
    tool_filter: ToolFilter = None,
    use_structured_content: bool = False,
    max_retry_attempts: int = 0,
    retry_backoff_seconds_base: float = 1.0,
    message_handler: MessageHandlerFnT | None = None,
    require_approval: RequireApprovalSetting = None,
    failure_error_function: ToolErrorFunction
    | None
    | _UnsetType = _UNSET,
)

Create a new MCP server based on the HTTP with SSE transport.

Parameters:

Name Type Description Default
params MCPServerSseParams

The params that configure the server. This includes the URL of the server, the headers to send to the server, the timeout for the HTTP request, and the timeout for the SSE connection.

 required
cache_tools_list bool

Whether to cache the tools list. If True, the tools list will be cached and only fetched from the server once. If False, the tools list will be fetched from the server on each call to list_tools(). The cache can be invalidated by calling invalidate_tools_cache(). You should set this to True if you know the server will not change its tools list, because it can drastically improve latency (by avoiding a round-trip to the server every time).

 False
name str | None

A readable name for the server. If not provided, we'll create one from the URL.

 None
client_session_timeout_seconds float | None

the read timeout passed to the MCP ClientSession.

 5
tool_filter ToolFilter

The tool filter to use for filtering tools.

 None
use_structured_content bool

Whether to use tool_result.structured_content when calling an MCP tool. Defaults to False for backwards compatibility - most MCP servers still include the structured content in the tool_result.content, and using it by default will cause duplicate content. You can set this to True if you know the server will not duplicate the structured content in the tool_result.content.

 False
max_retry_attempts int

Number of times to retry failed list_tools/call_tool calls. Defaults to no retries.

 0
retry_backoff_seconds_base float

The base delay, in seconds, for exponential backoff between retries.

 1.0
message_handler MessageHandlerFnT | None

Optional handler invoked for session messages as delivered by the ClientSession.

 None
require_approval RequireApprovalSetting

Approval policy for tools on this server. Accepts "always"/"never", a dict of tool names to those values, or an object with always/never tool lists.

 None
failure_error_function ToolErrorFunction | None | _UnsetType

Optional function used to convert MCP tool failures into a model-visible error message. If explicitly set to None, tool errors will be raised instead of converted. If left unset, the agent-level configuration (or SDK default) will be used.

 _UNSET
Source code in src/agents/mcp/server.py 
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def __init__(
    self,
    params: MCPServerSseParams,
    cache_tools_list: bool = False,
    name: str | None = None,
    client_session_timeout_seconds: float | None = 5,
    tool_filter: ToolFilter = None,
    use_structured_content: bool = False,
    max_retry_attempts: int = 0,
    retry_backoff_seconds_base: float = 1.0,
    message_handler: MessageHandlerFnT | None = None,
    require_approval: RequireApprovalSetting = None,
    failure_error_function: ToolErrorFunction | None | _UnsetType = _UNSET,
):
    """Create a new MCP server based on the HTTP with SSE transport.

    Args:
        params: The params that configure the server. This includes the URL of the server,
            the headers to send to the server, the timeout for the HTTP request, and the
            timeout for the SSE connection.

        cache_tools_list: Whether to cache the tools list. If `True`, the tools list will be
            cached and only fetched from the server once. If `False`, the tools list will be
            fetched from the server on each call to `list_tools()`. The cache can be
            invalidated by calling `invalidate_tools_cache()`. You should set this to `True`
            if you know the server will not change its tools list, because it can drastically
            improve latency (by avoiding a round-trip to the server every time).

        name: A readable name for the server. If not provided, we'll create one from the
            URL.

        client_session_timeout_seconds: the read timeout passed to the MCP ClientSession.
        tool_filter: The tool filter to use for filtering tools.
        use_structured_content: Whether to use `tool_result.structured_content` when calling an
            MCP tool. Defaults to False for backwards compatibility - most MCP servers still
            include the structured content in the `tool_result.content`, and using it by
            default will cause duplicate content. You can set this to True if you know the
            server will not duplicate the structured content in the `tool_result.content`.
        max_retry_attempts: Number of times to retry failed list_tools/call_tool calls.
            Defaults to no retries.
        retry_backoff_seconds_base: The base delay, in seconds, for exponential
            backoff between retries.
        message_handler: Optional handler invoked for session messages as delivered by the
            ClientSession.
        require_approval: Approval policy for tools on this server. Accepts "always"/"never",
            a dict of tool names to those values, or an object with always/never tool lists.
        failure_error_function: Optional function used to convert MCP tool failures into
            a model-visible error message. If explicitly set to None, tool errors will be
            raised instead of converted. If left unset, the agent-level configuration (or
            SDK default) will be used.
    """
    super().__init__(
        cache_tools_list,
        client_session_timeout_seconds,
        tool_filter,
        use_structured_content,
        max_retry_attempts,
        retry_backoff_seconds_base,
        message_handler=message_handler,
        require_approval=require_approval,
        failure_error_function=failure_error_function,
    )

    self.params = params
    self._name = name or f"sse: {self.params['url']}"

create_streams 

create_streams() -> AbstractAsyncContextManager[
    tuple[
        MemoryObjectReceiveStream[
            SessionMessage | Exception
        ],
        MemoryObjectSendStream[SessionMessage],
        GetSessionIdCallback | None,
    ]
]

Create the streams for the server.

Source code in src/agents/mcp/server.py 
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def create_streams(
    self,
) -> AbstractAsyncContextManager[
    tuple[
        MemoryObjectReceiveStream[SessionMessage | Exception],
        MemoryObjectSendStream[SessionMessage],
        GetSessionIdCallback | None,
    ]
]:
    """Create the streams for the server."""
    return sse_client(
        url=self.params["url"],
        headers=self.params.get("headers", None),
        timeout=self.params.get("timeout", 5),
        sse_read_timeout=self.params.get("sse_read_timeout", 60 * 5),
    )

connect async 

connect()

Connect to the server.

Source code in src/agents/mcp/server.py 
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async def connect(self):
    """Connect to the server."""
    connection_succeeded = False
    try:
        transport = await self.exit_stack.enter_async_context(self.create_streams())
        # streamablehttp_client returns (read, write, get_session_id)
        # sse_client returns (read, write)

        read, write, *_ = transport

        session = await self.exit_stack.enter_async_context(
            ClientSession(
                read,
                write,
                timedelta(seconds=self.client_session_timeout_seconds)
                if self.client_session_timeout_seconds
                else None,
                message_handler=self.message_handler,
            )
        )
        server_result = await session.initialize()
        self.server_initialize_result = server_result
        self.session = session
        connection_succeeded = True
    except Exception as e:
        # Try to extract HTTP error from exception or ExceptionGroup
        http_error = self._extract_http_error_from_exception(e)
        if http_error:
            self._raise_user_error_for_http_error(http_error)

        # For CancelledError, preserve cancellation semantics - don't wrap it.
        # If it's masking an HTTP error, cleanup() will extract and raise UserError.
        if isinstance(e, asyncio.CancelledError):
            raise

        # For HTTP-related errors, wrap them
        if isinstance(e, (httpx.HTTPStatusError, httpx.ConnectError, httpx.TimeoutException)):
            self._raise_user_error_for_http_error(e)

        # For other errors, re-raise as-is (don't wrap non-HTTP errors)
        raise
    finally:
        # Always attempt cleanup on error, but suppress cleanup errors that mask the original
        if not connection_succeeded:
            try:
                await self.cleanup()
            except UserError:
                # Re-raise UserError from cleanup (contains the real HTTP error)
                raise
            except Exception as cleanup_error:
                # Suppress RuntimeError about cancel scopes during cleanup - this is a known
                # issue with the MCP library's async generator cleanup and shouldn't mask the
                # original error
                if isinstance(cleanup_error, RuntimeError) and "cancel scope" in str(
                    cleanup_error
                ):
                    logger.debug(
                        f"Ignoring cancel scope error during cleanup of MCP server "
                        f"'{self.name}': {cleanup_error}"
                    )
                else:
                    # Log other cleanup errors but don't raise - original error is more
                    # important
                    logger.warning(
                        f"Error during cleanup of MCP server '{self.name}': {cleanup_error}"
                    )

cleanup async 

cleanup()

Cleanup the server.

Source code in src/agents/mcp/server.py 
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async def cleanup(self):
    """Cleanup the server."""
    async with self._cleanup_lock:
        # Only raise HTTP errors if we're cleaning up after a failed connection.
        # During normal teardown (via __aexit__), log but don't raise to avoid
        # masking the original exception.
        is_failed_connection_cleanup = self.session is None

        try:
            await self.exit_stack.aclose()
        except asyncio.CancelledError as e:
            logger.debug(f"Cleanup cancelled for MCP server '{self.name}': {e}")
            raise
        except BaseExceptionGroup as eg:
            # Extract HTTP errors from ExceptionGroup raised during cleanup
            # This happens when background tasks fail (e.g., HTTP errors)
            http_error = None
            connect_error = None
            timeout_error = None
            error_message = f"Failed to connect to MCP server '{self.name}': "

            for exc in eg.exceptions:
                if isinstance(exc, httpx.HTTPStatusError):
                    http_error = exc
                elif isinstance(exc, httpx.ConnectError):
                    connect_error = exc
                elif isinstance(exc, httpx.TimeoutException):
                    timeout_error = exc

            # Only raise HTTP errors if we're cleaning up after a failed connection.
            # During normal teardown, log them instead.
            if http_error:
                if is_failed_connection_cleanup:
                    error_message += f"HTTP error {http_error.response.status_code} ({http_error.response.reason_phrase})"  # noqa: E501
                    raise UserError(error_message) from http_error
                else:
                    # Normal teardown - log but don't raise
                    logger.warning(
                        f"HTTP error during cleanup of MCP server '{self.name}': {http_error}"
                    )
            elif connect_error:
                if is_failed_connection_cleanup:
                    error_message += "Could not reach the server."
                    raise UserError(error_message) from connect_error
                else:
                    logger.warning(
                        f"Connection error during cleanup of MCP server '{self.name}': {connect_error}"  # noqa: E501
                    )
            elif timeout_error:
                if is_failed_connection_cleanup:
                    error_message += "Connection timeout."
                    raise UserError(error_message) from timeout_error
                else:
                    logger.warning(
                        f"Timeout error during cleanup of MCP server '{self.name}': {timeout_error}"  # noqa: E501
                    )
            else:
                # No HTTP error found, suppress RuntimeError about cancel scopes
                has_cancel_scope_error = any(
                    isinstance(exc, RuntimeError) and "cancel scope" in str(exc)
                    for exc in eg.exceptions
                )
                if has_cancel_scope_error:
                    logger.debug(f"Ignoring cancel scope error during cleanup: {eg}")
                else:
                    logger.error(f"Error cleaning up server: {eg}")
        except Exception as e:
            # Suppress RuntimeError about cancel scopes - this is a known issue with the MCP
            # library when background tasks fail during async generator cleanup
            if isinstance(e, RuntimeError) and "cancel scope" in str(e):
                logger.debug(f"Ignoring cancel scope error during cleanup: {e}")
            else:
                logger.error(f"Error cleaning up server: {e}")
        finally:
            self.session = None

list_tools async 

list_tools(
    run_context: RunContextWrapper[Any] | None = None,
    agent: AgentBase | None = None,
) -> list[Tool]

List the tools available on the server.

Source code in src/agents/mcp/server.py 
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async def list_tools(
    self,
    run_context: RunContextWrapper[Any] | None = None,
    agent: AgentBase | None = None,
) -> list[MCPTool]:
    """List the tools available on the server."""
    if not self.session:
        raise UserError("Server not initialized. Make sure you call `connect()` first.")
    session = self.session
    assert session is not None

    try:
        # Return from cache if caching is enabled, we have tools, and the cache is not dirty
        if self.cache_tools_list and not self._cache_dirty and self._tools_list:
            tools = self._tools_list
        else:
            # Fetch the tools from the server
            result = await self._run_with_retries(lambda: session.list_tools())
            self._tools_list = result.tools
            self._cache_dirty = False
            tools = self._tools_list

        # Filter tools based on tool_filter
        filtered_tools = tools
        if self.tool_filter is not None:
            filtered_tools = await self._apply_tool_filter(filtered_tools, run_context, agent)
        return filtered_tools
    except httpx.HTTPStatusError as e:
        status_code = e.response.status_code
        raise UserError(
            f"Failed to list tools from MCP server '{self.name}': HTTP error {status_code}"
        ) from e
    except httpx.ConnectError as e:
        raise UserError(
            f"Failed to list tools from MCP server '{self.name}': Connection lost. "
            f"The server may have disconnected."
        ) from e

call_tool async 

call_tool(
    tool_name: str, arguments: dict[str, Any] | None
) -> CallToolResult

Invoke a tool on the server.

Source code in src/agents/mcp/server.py 
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async def call_tool(self, tool_name: str, arguments: dict[str, Any] | None) -> CallToolResult:
    """Invoke a tool on the server."""
    if not self.session:
        raise UserError("Server not initialized. Make sure you call `connect()` first.")
    session = self.session
    assert session is not None

    try:
        return await self._run_with_retries(lambda: session.call_tool(tool_name, arguments))
    except httpx.HTTPStatusError as e:
        status_code = e.response.status_code
        raise UserError(
            f"Failed to call tool '{tool_name}' on MCP server '{self.name}': "
            f"HTTP error {status_code}"
        ) from e
    except httpx.ConnectError as e:
        raise UserError(
            f"Failed to call tool '{tool_name}' on MCP server '{self.name}': Connection lost. "
            f"The server may have disconnected."
        ) from e

list_prompts async 

list_prompts() -> ListPromptsResult

List the prompts available on the server.

Source code in src/agents/mcp/server.py 
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async def list_prompts(
    self,
) -> ListPromptsResult:
    """List the prompts available on the server."""
    if not self.session:
        raise UserError("Server not initialized. Make sure you call `connect()` first.")

    return await self.session.list_prompts()

get_prompt async 

get_prompt(
    name: str, arguments: dict[str, Any] | None = None
) -> GetPromptResult

Get a specific prompt from the server.

Source code in src/agents/mcp/server.py 
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async def get_prompt(
    self, name: str, arguments: dict[str, Any] | None = None
) -> GetPromptResult:
    """Get a specific prompt from the server."""
    if not self.session:
        raise UserError("Server not initialized. Make sure you call `connect()` first.")

    return await self.session.get_prompt(name, arguments)

invalidate_tools_cache 

invalidate_tools_cache()

Invalidate the tools cache.

Source code in src/agents/mcp/server.py 
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def invalidate_tools_cache(self):
    """Invalidate the tools cache."""
    self._cache_dirty = True

MCPServerStreamableHttpParams

Bases: TypedDict

Mirrors the params inmcp.client.streamable_http.streamablehttp_client.

Source code in src/agents/mcp/server.py 
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class MCPServerStreamableHttpParams(TypedDict):
    """Mirrors the params in`mcp.client.streamable_http.streamablehttp_client`."""

    url: str
    """The URL of the server."""

    headers: NotRequired[dict[str, str]]
    """The headers to send to the server."""

    timeout: NotRequired[timedelta | float]
    """The timeout for the HTTP request. Defaults to 5 seconds."""

    sse_read_timeout: NotRequired[timedelta | float]
    """The timeout for the SSE connection, in seconds. Defaults to 5 minutes."""

    terminate_on_close: NotRequired[bool]
    """Terminate on close"""

    httpx_client_factory: NotRequired[HttpClientFactory]
    """Custom HTTP client factory for configuring httpx.AsyncClient behavior."""

url instance-attribute 

url: str

The URL of the server.

headers instance-attribute 

headers: NotRequired[dict[str, str]]

The headers to send to the server.

timeout instance-attribute 

timeout: NotRequired[timedelta | float]

The timeout for the HTTP request. Defaults to 5 seconds.

sse_read_timeout instance-attribute 

sse_read_timeout: NotRequired[timedelta | float]

The timeout for the SSE connection, in seconds. Defaults to 5 minutes.

terminate_on_close instance-attribute 

terminate_on_close: NotRequired[bool]

Terminate on close

httpx_client_factory instance-attribute 

httpx_client_factory: NotRequired[HttpClientFactory]

Custom HTTP client factory for configuring httpx.AsyncClient behavior.

MCPServerStreamableHttp

Bases: _MCPServerWithClientSession

MCP server implementation that uses the Streamable HTTP transport. See the [spec] (https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http) for details.

Source code in src/agents/mcp/server.py 
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class MCPServerStreamableHttp(_MCPServerWithClientSession):
    """MCP server implementation that uses the Streamable HTTP transport. See the [spec]
    (https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http)
    for details.
    """

    def __init__(
        self,
        params: MCPServerStreamableHttpParams,
        cache_tools_list: bool = False,
        name: str | None = None,
        client_session_timeout_seconds: float | None = 5,
        tool_filter: ToolFilter = None,
        use_structured_content: bool = False,
        max_retry_attempts: int = 0,
        retry_backoff_seconds_base: float = 1.0,
        message_handler: MessageHandlerFnT | None = None,
        require_approval: RequireApprovalSetting = None,
        failure_error_function: ToolErrorFunction | None | _UnsetType = _UNSET,
    ):
        """Create a new MCP server based on the Streamable HTTP transport.

        Args:
            params: The params that configure the server. This includes the URL of the server,
                the headers to send to the server, the timeout for the HTTP request, the
                timeout for the Streamable HTTP connection, whether we need to
                terminate on close, and an optional custom HTTP client factory.

            cache_tools_list: Whether to cache the tools list. If `True`, the tools list will be
                cached and only fetched from the server once. If `False`, the tools list will be
                fetched from the server on each call to `list_tools()`. The cache can be
                invalidated by calling `invalidate_tools_cache()`. You should set this to `True`
                if you know the server will not change its tools list, because it can drastically
                improve latency (by avoiding a round-trip to the server every time).

            name: A readable name for the server. If not provided, we'll create one from the
                URL.

            client_session_timeout_seconds: the read timeout passed to the MCP ClientSession.
            tool_filter: The tool filter to use for filtering tools.
            use_structured_content: Whether to use `tool_result.structured_content` when calling an
                MCP tool. Defaults to False for backwards compatibility - most MCP servers still
                include the structured content in the `tool_result.content`, and using it by
                default will cause duplicate content. You can set this to True if you know the
                server will not duplicate the structured content in the `tool_result.content`.
            max_retry_attempts: Number of times to retry failed list_tools/call_tool calls.
                Defaults to no retries.
            retry_backoff_seconds_base: The base delay, in seconds, for exponential
                backoff between retries.
            message_handler: Optional handler invoked for session messages as delivered by the
                ClientSession.
            require_approval: Approval policy for tools on this server. Accepts "always"/"never",
                a dict of tool names to those values, or an object with always/never tool lists.
            failure_error_function: Optional function used to convert MCP tool failures into
                a model-visible error message. If explicitly set to None, tool errors will be
                raised instead of converted. If left unset, the agent-level configuration (or
                SDK default) will be used.
        """
        super().__init__(
            cache_tools_list,
            client_session_timeout_seconds,
            tool_filter,
            use_structured_content,
            max_retry_attempts,
            retry_backoff_seconds_base,
            message_handler=message_handler,
            require_approval=require_approval,
            failure_error_function=failure_error_function,
        )

        self.params = params
        self._name = name or f"streamable_http: {self.params['url']}"

    def create_streams(
        self,
    ) -> AbstractAsyncContextManager[
        tuple[
            MemoryObjectReceiveStream[SessionMessage | Exception],
            MemoryObjectSendStream[SessionMessage],
            GetSessionIdCallback | None,
        ]
    ]:
        """Create the streams for the server."""
        # Only pass httpx_client_factory if it's provided
        if "httpx_client_factory" in self.params:
            return streamablehttp_client(
                url=self.params["url"],
                headers=self.params.get("headers", None),
                timeout=self.params.get("timeout", 5),
                sse_read_timeout=self.params.get("sse_read_timeout", 60 * 5),
                terminate_on_close=self.params.get("terminate_on_close", True),
                httpx_client_factory=self.params["httpx_client_factory"],
            )
        else:
            return streamablehttp_client(
                url=self.params["url"],
                headers=self.params.get("headers", None),
                timeout=self.params.get("timeout", 5),
                sse_read_timeout=self.params.get("sse_read_timeout", 60 * 5),
                terminate_on_close=self.params.get("terminate_on_close", True),
            )

    @property
    def name(self) -> str:
        """A readable name for the server."""
        return self._name

name property 

name: str

A readable name for the server.

__init__ 

__init__(
    params: MCPServerStreamableHttpParams,
    cache_tools_list: bool = False,
    name: str | None = None,
    client_session_timeout_seconds: float | None = 5,
    tool_filter: ToolFilter = None,
    use_structured_content: bool = False,
    max_retry_attempts: int = 0,
    retry_backoff_seconds_base: float = 1.0,
    message_handler: MessageHandlerFnT | None = None,
    require_approval: RequireApprovalSetting = None,
    failure_error_function: ToolErrorFunction
    | None
    | _UnsetType = _UNSET,
)

Create a new MCP server based on the Streamable HTTP transport.

Parameters:

Name Type Description Default
params MCPServerStreamableHttpParams

The params that configure the server. This includes the URL of the server, the headers to send to the server, the timeout for the HTTP request, the timeout for the Streamable HTTP connection, whether we need to terminate on close, and an optional custom HTTP client factory.

 required
cache_tools_list bool

Whether to cache the tools list. If True, the tools list will be cached and only fetched from the server once. If False, the tools list will be fetched from the server on each call to list_tools(). The cache can be invalidated by calling invalidate_tools_cache(). You should set this to True if you know the server will not change its tools list, because it can drastically improve latency (by avoiding a round-trip to the server every time).

 False
name str | None

A readable name for the server. If not provided, we'll create one from the URL.

 None
client_session_timeout_seconds float | None

the read timeout passed to the MCP ClientSession.

 5
tool_filter ToolFilter

The tool filter to use for filtering tools.

 None
use_structured_content bool

Whether to use tool_result.structured_content when calling an MCP tool. Defaults to False for backwards compatibility - most MCP servers still include the structured content in the tool_result.content, and using it by default will cause duplicate content. You can set this to True if you know the server will not duplicate the structured content in the tool_result.content.

 False
max_retry_attempts int

Number of times to retry failed list_tools/call_tool calls. Defaults to no retries.

 0
retry_backoff_seconds_base float

The base delay, in seconds, for exponential backoff between retries.

 1.0
message_handler MessageHandlerFnT | None

Optional handler invoked for session messages as delivered by the ClientSession.

 None
require_approval RequireApprovalSetting

Approval policy for tools on this server. Accepts "always"/"never", a dict of tool names to those values, or an object with always/never tool lists.

 None
failure_error_function ToolErrorFunction | None | _UnsetType

Optional function used to convert MCP tool failures into a model-visible error message. If explicitly set to None, tool errors will be raised instead of converted. If left unset, the agent-level configuration (or SDK default) will be used.

 _UNSET
Source code in src/agents/mcp/server.py 
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def __init__(
    self,
    params: MCPServerStreamableHttpParams,
    cache_tools_list: bool = False,
    name: str | None = None,
    client_session_timeout_seconds: float | None = 5,
    tool_filter: ToolFilter = None,
    use_structured_content: bool = False,
    max_retry_attempts: int = 0,
    retry_backoff_seconds_base: float = 1.0,
    message_handler: MessageHandlerFnT | None = None,
    require_approval: RequireApprovalSetting = None,
    failure_error_function: ToolErrorFunction | None | _UnsetType = _UNSET,
):
    """Create a new MCP server based on the Streamable HTTP transport.

    Args:
        params: The params that configure the server. This includes the URL of the server,
            the headers to send to the server, the timeout for the HTTP request, the
            timeout for the Streamable HTTP connection, whether we need to
            terminate on close, and an optional custom HTTP client factory.

        cache_tools_list: Whether to cache the tools list. If `True`, the tools list will be
            cached and only fetched from the server once. If `False`, the tools list will be
            fetched from the server on each call to `list_tools()`. The cache can be
            invalidated by calling `invalidate_tools_cache()`. You should set this to `True`
            if you know the server will not change its tools list, because it can drastically
            improve latency (by avoiding a round-trip to the server every time).

        name: A readable name for the server. If not provided, we'll create one from the
            URL.

        client_session_timeout_seconds: the read timeout passed to the MCP ClientSession.
        tool_filter: The tool filter to use for filtering tools.
        use_structured_content: Whether to use `tool_result.structured_content` when calling an
            MCP tool. Defaults to False for backwards compatibility - most MCP servers still
            include the structured content in the `tool_result.content`, and using it by
            default will cause duplicate content. You can set this to True if you know the
            server will not duplicate the structured content in the `tool_result.content`.
        max_retry_attempts: Number of times to retry failed list_tools/call_tool calls.
            Defaults to no retries.
        retry_backoff_seconds_base: The base delay, in seconds, for exponential
            backoff between retries.
        message_handler: Optional handler invoked for session messages as delivered by the
            ClientSession.
        require_approval: Approval policy for tools on this server. Accepts "always"/"never",
            a dict of tool names to those values, or an object with always/never tool lists.
        failure_error_function: Optional function used to convert MCP tool failures into
            a model-visible error message. If explicitly set to None, tool errors will be
            raised instead of converted. If left unset, the agent-level configuration (or
            SDK default) will be used.
    """
    super().__init__(
        cache_tools_list,
        client_session_timeout_seconds,
        tool_filter,
        use_structured_content,
        max_retry_attempts,
        retry_backoff_seconds_base,
        message_handler=message_handler,
        require_approval=require_approval,
        failure_error_function=failure_error_function,
    )

    self.params = params
    self._name = name or f"streamable_http: {self.params['url']}"

create_streams 

create_streams() -> AbstractAsyncContextManager[
    tuple[
        MemoryObjectReceiveStream[
            SessionMessage | Exception
        ],
        MemoryObjectSendStream[SessionMessage],
        GetSessionIdCallback | None,
    ]
]

Create the streams for the server.

Source code in src/agents/mcp/server.py 
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def create_streams(
    self,
) -> AbstractAsyncContextManager[
    tuple[
        MemoryObjectReceiveStream[SessionMessage | Exception],
        MemoryObjectSendStream[SessionMessage],
        GetSessionIdCallback | None,
    ]
]:
    """Create the streams for the server."""
    # Only pass httpx_client_factory if it's provided
    if "httpx_client_factory" in self.params:
        return streamablehttp_client(
            url=self.params["url"],
            headers=self.params.get("headers", None),
            timeout=self.params.get("timeout", 5),
            sse_read_timeout=self.params.get("sse_read_timeout", 60 * 5),
            terminate_on_close=self.params.get("terminate_on_close", True),
            httpx_client_factory=self.params["httpx_client_factory"],
        )
    else:
        return streamablehttp_client(
            url=self.params["url"],
            headers=self.params.get("headers", None),
            timeout=self.params.get("timeout", 5),
            sse_read_timeout=self.params.get("sse_read_timeout", 60 * 5),
            terminate_on_close=self.params.get("terminate_on_close", True),
        )

connect async 

connect()

Connect to the server.

Source code in src/agents/mcp/server.py 
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async def connect(self):
    """Connect to the server."""
    connection_succeeded = False
    try:
        transport = await self.exit_stack.enter_async_context(self.create_streams())
        # streamablehttp_client returns (read, write, get_session_id)
        # sse_client returns (read, write)

        read, write, *_ = transport

        session = await self.exit_stack.enter_async_context(
            ClientSession(
                read,
                write,
                timedelta(seconds=self.client_session_timeout_seconds)
                if self.client_session_timeout_seconds
                else None,
                message_handler=self.message_handler,
            )
        )
        server_result = await session.initialize()
        self.server_initialize_result = server_result
        self.session = session
        connection_succeeded = True
    except Exception as e:
        # Try to extract HTTP error from exception or ExceptionGroup
        http_error = self._extract_http_error_from_exception(e)
        if http_error:
            self._raise_user_error_for_http_error(http_error)

        # For CancelledError, preserve cancellation semantics - don't wrap it.
        # If it's masking an HTTP error, cleanup() will extract and raise UserError.
        if isinstance(e, asyncio.CancelledError):
            raise

        # For HTTP-related errors, wrap them
        if isinstance(e, (httpx.HTTPStatusError, httpx.ConnectError, httpx.TimeoutException)):
            self._raise_user_error_for_http_error(e)

        # For other errors, re-raise as-is (don't wrap non-HTTP errors)
        raise
    finally:
        # Always attempt cleanup on error, but suppress cleanup errors that mask the original
        if not connection_succeeded:
            try:
                await self.cleanup()
            except UserError:
                # Re-raise UserError from cleanup (contains the real HTTP error)
                raise
            except Exception as cleanup_error:
                # Suppress RuntimeError about cancel scopes during cleanup - this is a known
                # issue with the MCP library's async generator cleanup and shouldn't mask the
                # original error
                if isinstance(cleanup_error, RuntimeError) and "cancel scope" in str(
                    cleanup_error
                ):
                    logger.debug(
                        f"Ignoring cancel scope error during cleanup of MCP server "
                        f"'{self.name}': {cleanup_error}"
                    )
                else:
                    # Log other cleanup errors but don't raise - original error is more
                    # important
                    logger.warning(
                        f"Error during cleanup of MCP server '{self.name}': {cleanup_error}"
                    )

cleanup async 

cleanup()

Cleanup the server.

Source code in src/agents/mcp/server.py 
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async def cleanup(self):
    """Cleanup the server."""
    async with self._cleanup_lock:
        # Only raise HTTP errors if we're cleaning up after a failed connection.
        # During normal teardown (via __aexit__), log but don't raise to avoid
        # masking the original exception.
        is_failed_connection_cleanup = self.session is None

        try:
            await self.exit_stack.aclose()
        except asyncio.CancelledError as e:
            logger.debug(f"Cleanup cancelled for MCP server '{self.name}': {e}")
            raise
        except BaseExceptionGroup as eg:
            # Extract HTTP errors from ExceptionGroup raised during cleanup
            # This happens when background tasks fail (e.g., HTTP errors)
            http_error = None
            connect_error = None
            timeout_error = None
            error_message = f"Failed to connect to MCP server '{self.name}': "

            for exc in eg.exceptions:
                if isinstance(exc, httpx.HTTPStatusError):
                    http_error = exc
                elif isinstance(exc, httpx.ConnectError):
                    connect_error = exc
                elif isinstance(exc, httpx.TimeoutException):
                    timeout_error = exc

            # Only raise HTTP errors if we're cleaning up after a failed connection.
            # During normal teardown, log them instead.
            if http_error:
                if is_failed_connection_cleanup:
                    error_message += f"HTTP error {http_error.response.status_code} ({http_error.response.reason_phrase})"  # noqa: E501
                    raise UserError(error_message) from http_error
                else:
                    # Normal teardown - log but don't raise
                    logger.warning(
                        f"HTTP error during cleanup of MCP server '{self.name}': {http_error}"
                    )
            elif connect_error:
                if is_failed_connection_cleanup:
                    error_message += "Could not reach the server."
                    raise UserError(error_message) from connect_error
                else:
                    logger.warning(
                        f"Connection error during cleanup of MCP server '{self.name}': {connect_error}"  # noqa: E501
                    )
            elif timeout_error:
                if is_failed_connection_cleanup:
                    error_message += "Connection timeout."
                    raise UserError(error_message) from timeout_error
                else:
                    logger.warning(
                        f"Timeout error during cleanup of MCP server '{self.name}': {timeout_error}"  # noqa: E501
                    )
            else:
                # No HTTP error found, suppress RuntimeError about cancel scopes
                has_cancel_scope_error = any(
                    isinstance(exc, RuntimeError) and "cancel scope" in str(exc)
                    for exc in eg.exceptions
                )
                if has_cancel_scope_error:
                    logger.debug(f"Ignoring cancel scope error during cleanup: {eg}")
                else:
                    logger.error(f"Error cleaning up server: {eg}")
        except Exception as e:
            # Suppress RuntimeError about cancel scopes - this is a known issue with the MCP
            # library when background tasks fail during async generator cleanup
            if isinstance(e, RuntimeError) and "cancel scope" in str(e):
                logger.debug(f"Ignoring cancel scope error during cleanup: {e}")
            else:
                logger.error(f"Error cleaning up server: {e}")
        finally:
            self.session = None

list_tools async 

list_tools(
    run_context: RunContextWrapper[Any] | None = None,
    agent: AgentBase | None = None,
) -> list[Tool]

List the tools available on the server.

Source code in src/agents/mcp/server.py 
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async def list_tools(
    self,
    run_context: RunContextWrapper[Any] | None = None,
    agent: AgentBase | None = None,
) -> list[MCPTool]:
    """List the tools available on the server."""
    if not self.session:
        raise UserError("Server not initialized. Make sure you call `connect()` first.")
    session = self.session
    assert session is not None

    try:
        # Return from cache if caching is enabled, we have tools, and the cache is not dirty
        if self.cache_tools_list and not self._cache_dirty and self._tools_list:
            tools = self._tools_list
        else:
            # Fetch the tools from the server
            result = await self._run_with_retries(lambda: session.list_tools())
            self._tools_list = result.tools
            self._cache_dirty = False
            tools = self._tools_list

        # Filter tools based on tool_filter
        filtered_tools = tools
        if self.tool_filter is not None:
            filtered_tools = await self._apply_tool_filter(filtered_tools, run_context, agent)
        return filtered_tools
    except httpx.HTTPStatusError as e:
        status_code = e.response.status_code
        raise UserError(
            f"Failed to list tools from MCP server '{self.name}': HTTP error {status_code}"
        ) from e
    except httpx.ConnectError as e:
        raise UserError(
            f"Failed to list tools from MCP server '{self.name}': Connection lost. "
            f"The server may have disconnected."
        ) from e

call_tool async 

call_tool(
    tool_name: str, arguments: dict[str, Any] | None
) -> CallToolResult

Invoke a tool on the server.

Source code in src/agents/mcp/server.py 
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async def call_tool(self, tool_name: str, arguments: dict[str, Any] | None) -> CallToolResult:
    """Invoke a tool on the server."""
    if not self.session:
        raise UserError("Server not initialized. Make sure you call `connect()` first.")
    session = self.session
    assert session is not None

    try:
        return await self._run_with_retries(lambda: session.call_tool(tool_name, arguments))
    except httpx.HTTPStatusError as e:
        status_code = e.response.status_code
        raise UserError(
            f"Failed to call tool '{tool_name}' on MCP server '{self.name}': "
            f"HTTP error {status_code}"
        ) from e
    except httpx.ConnectError as e:
        raise UserError(
            f"Failed to call tool '{tool_name}' on MCP server '{self.name}': Connection lost. "
            f"The server may have disconnected."
        ) from e

list_prompts async 

list_prompts() -> ListPromptsResult

List the prompts available on the server.

Source code in src/agents/mcp/server.py 
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async def list_prompts(
    self,
) -> ListPromptsResult:
    """List the prompts available on the server."""
    if not self.session:
        raise UserError("Server not initialized. Make sure you call `connect()` first.")

    return await self.session.list_prompts()

get_prompt async 

get_prompt(
    name: str, arguments: dict[str, Any] | None = None
) -> GetPromptResult

Get a specific prompt from the server.

Source code in src/agents/mcp/server.py 
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async def get_prompt(
    self, name: str, arguments: dict[str, Any] | None = None
) -> GetPromptResult:
    """Get a specific prompt from the server."""
    if not self.session:
        raise UserError("Server not initialized. Make sure you call `connect()` first.")

    return await self.session.get_prompt(name, arguments)

invalidate_tools_cache 

invalidate_tools_cache()

Invalidate the tools cache.

Source code in src/agents/mcp/server.py 
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def invalidate_tools_cache(self):
    """Invalidate the tools cache."""
    self._cache_dirty = True