feat: add message to ProgressNotification

src/mcp/client/session.py

@@ -167,7 +167,11 @@ async def send_ping(self) -> types.EmptyResult:
         )
 
     async def send_progress_notification(
-        self, progress_token: str | int, progress: float, total: float | None = None
+        self,
+        progress_token: str | int,
+        progress: float,
+        total: float | None = None,
+        message: str | None = None,
     ) -> None:
         """Send a progress notification."""
         await self.send_notification(
@@ -178,6 +182,7 @@ async def send_progress_notification(
                         progressToken=progress_token,
                         progress=progress,
                         total=total,
+                        message=message,
                     ),
                 ),
             )

src/mcp/server/fastmcp/server.py

@@ -621,13 +621,14 @@ def request_context(self) -> RequestContext[ServerSessionT, LifespanContextT]:
         return self._request_context
 
     async def report_progress(
-        self, progress: float, total: float | None = None
+        self, progress: float, total: float | None = None, message: str | None = None
     ) -> None:
         """Report progress for the current operation.
 
         Args:
             progress: Current progress value e.g. 24
             total: Optional total value e.g. 100
+            message: Optional message e.g. Starting render...
         """
 
         progress_token = (
@@ -640,7 +641,10 @@ async def report_progress(
             return
 
         await self.request_context.session.send_progress_notification(
-            progress_token=progress_token, progress=progress, total=total
+            progress_token=progress_token,
+            progress=progress,
+            total=total,
+            message=message,
         )
 
     async def read_resource(self, uri: str | AnyUrl) -> Iterable[ReadResourceContents]:

src/mcp/server/lowlevel/server.py

@@ -37,7 +37,8 @@ async def handle_list_resource_templates() -> list[types.ResourceTemplate]:
 3. Define notification handlers if needed:
    @server.progress_notification()
    async def handle_progress(
-       progress_token: str | int, progress: float, total: float | None
+       progress_token: str | int, progress: float, total: float | None,
+       message: str | None
    ) -> None:
        # Implementation
 
@@ -426,13 +427,18 @@ async def handler(req: types.CallToolRequest):
 
     def progress_notification(self):
         def decorator(
-            func: Callable[[str | int, float, float | None], Awaitable[None]],
+            func: Callable[
+                [str | int, float, float | None, str | None], Awaitable[None]
+            ],
         ):
             logger.debug("Registering handler for ProgressNotification")
 
             async def handler(req: types.ProgressNotification):
                 await func(
-                    req.params.progressToken, req.params.progress, req.params.total
+                    req.params.progressToken,
+                    req.params.progress,
+                    req.params.total,
+                    req.params.message,
                 )
 
             self.notification_handlers[types.ProgressNotification] = handler

src/mcp/server/session.py

@@ -261,7 +261,11 @@ async def send_ping(self) -> types.EmptyResult:
         )
 
     async def send_progress_notification(
-        self, progress_token: str | int, progress: float, total: float | None = None
+        self,
+        progress_token: str | int,
+        progress: float,
+        total: float | None = None,
+        message: str | None = None,
     ) -> None:
         """Send a progress notification."""
         await self.send_notification(
@@ -272,6 +276,7 @@ async def send_progress_notification(
                         progressToken=progress_token,
                         progress=progress,
                         total=total,
+                        message=message,
                     ),
                 )
             )

src/mcp/shared/progress.py

@@ -42,12 +42,13 @@ class ProgressContext(
     progress_token: ProgressToken
     total: float | None
     current: float = field(default=0.0, init=False)
+    message: str | None
 
     async def progress(self, amount: float) -> None:
         self.current += amount
 
         await self.session.send_progress_notification(
-            self.progress_token, self.current, total=self.total
+            self.progress_token, self.current, total=self.total, message=self.message
         )
 
 
@@ -77,7 +78,7 @@ def progress(
     if ctx.meta is None or ctx.meta.progressToken is None:
         raise ValueError("No progress token provided")
 
-    progress_ctx = ProgressContext(ctx.session, ctx.meta.progressToken, total)
+    progress_ctx = ProgressContext(ctx.session, ctx.meta.progressToken, total, None)
     try:
         yield progress_ctx
     finally:

src/mcp/shared/session.py

@@ -377,7 +377,11 @@ async def _received_notification(self, notification: ReceiveNotificationT) -> No
         """
 
     async def send_progress_notification(
-        self, progress_token: str | int, progress: float, total: float | None = None
+        self,
+        progress_token: str | int,
+        progress: float,
+        total: float | None = None,
+        message: str | None = None,
     ) -> None:
         """
         Sends a progress notification for a request that is currently being

src/mcp/types.py

@@ -337,6 +337,11 @@ class ProgressNotificationParams(NotificationParams):
     total is unknown.
     """
     total: float | None = None
+    """
+    Message related to progress. This should provide relevant human readable 
+    progress information.
+    """
+    message: str | None = None
     """Total number of items to process (or total progress required), if known."""
     model_config = ConfigDict(extra="allow")
 

tests/issues/test_176_progress_token.py

@@ -39,11 +39,11 @@ async def test_progress_token_zero_first_call():
         mock_session.send_progress_notification.call_count == 3
     ), "All progress notifications should be sent"
     mock_session.send_progress_notification.assert_any_call(
-        progress_token=0, progress=0.0, total=10.0
+        progress_token=0, progress=0.0, total=10.0, message=None
     )
     mock_session.send_progress_notification.assert_any_call(
-        progress_token=0, progress=5.0, total=10.0
+        progress_token=0, progress=5.0, total=10.0, message=None
     )
     mock_session.send_progress_notification.assert_any_call(
-        progress_token=0, progress=10.0, total=10.0
+        progress_token=0, progress=10.0, total=10.0, message=None
     )

tests/shared/test_progress_notifications.py

@@ -0,0 +1,214 @@
+import anyio
+import pytest
+
+import mcp.types as types
+from mcp.client.session import ClientSession
+from mcp.server import Server
+from mcp.server.lowlevel import NotificationOptions
+from mcp.server.models import InitializationOptions
+from mcp.server.session import ServerSession
+from mcp.shared.session import RequestResponder
+from mcp.types import (
+    JSONRPCMessage,
+)
+
+
+@pytest.mark.anyio
+async def test_bidirectional_progress_notifications():
+    """Test that both client and server can send progress notifications."""
+    # Create memory streams for client/server
+    server_to_client_send, server_to_client_receive = anyio.create_memory_object_stream[
+        JSONRPCMessage
+    ](5)
+    client_to_server_send, client_to_server_receive = anyio.create_memory_object_stream[
+        JSONRPCMessage
+    ](5)
+
+    # Run a server session so we can send progress updates in tool
+    async def run_server():
+        # Create a server session
+        async with ServerSession(
+            client_to_server_receive,
+            server_to_client_send,
+            InitializationOptions(
+                server_name="ProgressTestServer",
+                server_version="0.1.0",
+                capabilities=server.get_capabilities(NotificationOptions(), {}),
+            ),
+        ) as server_session:
+            global serv_sesh
+
+            serv_sesh = server_session
+            async for message in server_session.incoming_messages:
+                try:
+                    await server._handle_message(message, server_session, ())
+                except Exception as e:
+                    raise e
+
+    # Track progress updates
+    server_progress_updates = []
+    client_progress_updates = []
+
+    # Progress tokens
+    server_progress_token = "server_token_123"
+    client_progress_token = "client_token_456"
+
+    # Create a server with progress capability
+    server = Server(name="ProgressTestServer")
+
+    # Register progress handler
+    @server.progress_notification()
+    async def handle_progress(
+        progress_token: str | int,
+        progress: float,
+        total: float | None,
+        message: str | None,
+    ):
+        server_progress_updates.append(
+            {
+                "token": progress_token,
+                "progress": progress,
+                "total": total,
+                "message": message,
+            }
+        )
+
+    # Register list tool handler
+    @server.list_tools()
+    async def handle_list_tools() -> list[types.Tool]:
+        return [
+            types.Tool(
+                name="test_tool",
+                description="A tool that sends progress notifications <o/",
+                inputSchema={},
+            )
+        ]
+
+    # Register tool handler
+    @server.call_tool()
+    async def handle_call_tool(name: str, arguments: dict | None) -> list:
+        # Make sure we received a progress token
+        if name == "test_tool":
+            if arguments and "_meta" in arguments:
+                progressToken = arguments["_meta"]["progressToken"]
+
+                if not progressToken:
+                    raise ValueError("Empty progress token received")
+
+                if progressToken != client_progress_token:
+                    raise ValueError("Server sending back incorrect progressToken")
+
+                # Send progress notifications
+                await serv_sesh.send_progress_notification(
+                    progress_token=progressToken,
+                    progress=0.25,
+                    total=1.0,
+                    message="Server progress 25%",
+                )
+                await anyio.sleep(0.2)
+
+                await serv_sesh.send_progress_notification(
+                    progress_token=progressToken,
+                    progress=0.5,
+                    total=1.0,
+                    message="Server progress 50%",
+                )
+                await anyio.sleep(0.2)
+
+                await serv_sesh.send_progress_notification(
+                    progress_token=progressToken,
+                    progress=1.0,
+                    total=1.0,
+                    message="Server progress 100%",
+                )
+
+            else:
+                raise ValueError("Progress token not sent.")
+
+            return ["Tool executed successfully"]
+
+        raise ValueError(f"Unknown tool: {name}")
+
+    # Client message handler to store progress notifications
+    async def handle_client_message(
+        message: RequestResponder[types.ServerRequest, types.ClientResult]
+        | types.ServerNotification
+        | Exception,
+    ) -> None:
+        if isinstance(message, Exception):
+            raise message
+
+        if isinstance(message, types.ServerNotification):
+            if isinstance(message.root, types.ProgressNotification):
+                params = message.root.params
+                client_progress_updates.append(
+                    {
+                        "token": params.progressToken,
+                        "progress": params.progress,
+                        "total": params.total,
+                        "message": params.message,
+                    }
+                )
+
+    # Test using client
+    async with (
+        ClientSession(
+            server_to_client_receive,
+            client_to_server_send,
+            message_handler=handle_client_message,
+        ) as client_session,
+        anyio.create_task_group() as tg,
+    ):
+        # Start the server in a background task
+        tg.start_soon(run_server)
+
+        # Initialize the client connection
+        await client_session.initialize()
+
+        # Call list_tools with progress token
+        await client_session.list_tools()
+
+        # Call test_tool with progress token
+        await client_session.call_tool(
+            "test_tool", {"_meta": {"progressToken": client_progress_token}}
+        )
+
+        # Send progress notifications from client to server
+        await client_session.send_progress_notification(
+            progress_token=server_progress_token,
+            progress=0.33,
+            total=1.0,
+            message="Client progress 33%",
+        )
+
+        await client_session.send_progress_notification(
+            progress_token=server_progress_token,
+            progress=0.66,
+            total=1.0,
+            message="Client progress 66%",
+        )
+
+        await client_session.send_progress_notification(
+            progress_token=server_progress_token,
+            progress=1.0,
+            total=1.0,
+            message="Client progress 100%",
+        )
+
+        # Wait and exit
+        await anyio.sleep(1.0)
+        tg.cancel_scope.cancel()
+
+    # Verify client received progress updates from server
+    assert len(client_progress_updates) == 3
+    assert client_progress_updates[0]["token"] == client_progress_token
+    assert client_progress_updates[0]["progress"] == 0.25
+    assert client_progress_updates[0]["message"] == "Server progress 25%"
+    assert client_progress_updates[2]["progress"] == 1.0
+
+    # Verify server received progress updates from client
+    assert len(server_progress_updates) == 3
+    assert server_progress_updates[0]["token"] == server_progress_token
+    assert server_progress_updates[0]["progress"] == 0.33
+    assert server_progress_updates[0]["message"] == "Client progress 33%"
+    assert server_progress_updates[2]["progress"] == 1.0