fastmcp.client.messages

Classes

MessageHandler ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/messages.py#L11" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

This class is used to handle MCP messages sent to the client: notifications and transport-level exceptions. Users can override any of the hooks.

Server-initiated requests (ping, sampling, roots) never reach this handler: the stable MCP SDK v2's message_handler contract only delivers ServerNotification | Exception, so a request has no wire path here. Those are answered through the Client's dedicated callbacks instead — sampling_handler=, roots=, and elicitation_handler=.

Methods:

dispatch ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/messages.py#L26" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

dispatch(self, message: Message) -> None

on_message ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/messages.py#L54" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

on_message(self, message: Message) -> None

on_notification ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/messages.py#L57" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

on_notification(self, message: mcp_types.ServerNotification) -> None

on_exception ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/messages.py#L60" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

on_exception(self, message: Exception) -> None

on_progress ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/messages.py#L63" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

on_progress(self, message: mcp_types.ProgressNotification) -> None

on_logging_message ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/messages.py#L66" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

on_logging_message(self, message: mcp_types.LoggingMessageNotification) -> None

on_tool_list_changed ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/messages.py#L71" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

on_tool_list_changed(self, message: mcp_types.ToolListChangedNotification) -> None

on_resource_list_changed ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/messages.py#L76" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

on_resource_list_changed(self, message: mcp_types.ResourceListChangedNotification) -> None

on_prompt_list_changed ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/messages.py#L81" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

on_prompt_list_changed(self, message: mcp_types.PromptListChangedNotification) -> None

on_resource_updated ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/messages.py#L86" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

on_resource_updated(self, message: mcp_types.ResourceUpdatedNotification) -> None

on_cancelled ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/messages.py#L91" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

on_cancelled(self, message: mcp_types.CancelledNotification) -> None