feat(web): display negotiated MCP protocol version on ServerCard (#1324) (#1442)

* feat(web): show negotiated MCP protocol version on ServerCard (#1324)

Add optional protocolVersion to ConnectionState and render it as a
dimmed "MCP <version>" label at the end of the transport-badge/
description row on ServerCard, shown only when connected. The value
is plumbed through useInspectorClient as part of #1324.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* feat(core,web): surface negotiated protocolVersion end-to-end (#1324)

Plumb the MCP protocol version negotiated during initialize from the
InspectorClient through to the ServerCard so the active connected card
displays "MCP <version>".

The SDK Client doesn't expose protocolVersion; it stamps it onto the
transport via setProtocolVersion. MessageTrackingTransport now captures
it (and forwards to the base transport when present), so it works for
stdio too — whose base transport has no setProtocolVersion.

- core: MessageTrackingTransport captures + exposes protocolVersion;
  InspectorClient stores it, exposes getProtocolVersion(), dispatches a
  protocolVersionChange event, and clears it on disconnect.
- core: useInspectorClient subscribes and returns protocolVersion.
- web: App reads it from the hook (drops the hard-coded "2025-06-18")
  and InspectorView splices it onto the active server's connection.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* refactor(web): decouple initializeResult from protocolVersion (#1324 review)

Gate the initializeResult memo on serverInfo only, not protocolVersion.
initializeResult also drives the connected ViewHeader and Connection Info
modal, so requiring the version risked hiding the whole connected surface
in the edge case where it's absent. protocolVersion now flows through as
the optional field it already is everywhere downstream ('' reads as
unknown; the ServerCard label and modal value both tolerate it).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* refactor(web): drop redundant connected-check in InspectorView splice (#1324 review)

initializeResult is derived from connectionStatus in App's memo, so a
truthy initializeResult.protocolVersion already implies a live
connection — the extra connectionStatus === 'connected' guard in the
splice was redundant. ServerCard keeps its own status guard (dumb-
component robustness). No behavior change.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/web/src/App.tsx

@@ -600,6 +600,7 @@ function App() {
     clientCapabilities,
     serverInfo,
     instructions,
+    protocolVersion,
   } = useInspectorClient(inspectorClient);
   const { tools, refresh: refreshTools } = useManagedTools(
     inspectorClient,
@@ -880,19 +881,30 @@ function App() {
     };
   }, [inspectorClient]);
 
-  // Build the InitializeResult the connected ViewHeader expects from the
-  // hook's split fields. `protocolVersion` is hard-coded for now — the
-  // useInspectorClient hook doesn't expose it. TODO(#1324): consume the
-  // negotiated value once the hook surfaces it.
+  // Build the InitializeResult the connected ViewHeader / Connection Info
+  // modal expect from the hook's split fields. `protocolVersion` is the value
+  // the InspectorClient negotiated during initialize (#1324); it's dispatched
+  // alongside serverInfo, so in practice it's present whenever we're connected.
+  // We deliberately gate only on serverInfo (not protocolVersion): this object
+  // also drives the connected header and Connection Info modal, so a
+  // missing/edge-case version must not hide those. It flows through as the
+  // optional field it is everywhere downstream (the ServerCard label and the
+  // modal value both tolerate an empty string), so "" reads as "unknown".
   const initializeResult = useMemo<InitializeResult | undefined>(() => {
     if (connectionStatus !== "connected" || !serverInfo) return undefined;
     return {
-      protocolVersion: "2025-06-18",
+      protocolVersion: protocolVersion ?? "",
       capabilities: capabilities ?? {},
       serverInfo,
       ...(instructions ? { instructions } : {}),
     };
-  }, [connectionStatus, capabilities, serverInfo, instructions]);
+  }, [
+    connectionStatus,
+    capabilities,
+    serverInfo,
+    instructions,
+    protocolVersion,
+  ]);
 
   // The Server Info modal needs the active server's transport and (optional)
   // OAuth details — both are co-located here so the modal opens against the

clients/web/src/components/groups/ServerCard/ServerCard.stories.tsx

@@ -15,7 +15,10 @@ const httpConfig: MCPServerConfig = {
   url: "https://api.example.com/mcp",
 };
 
-const connected: ConnectionState = { status: "connected" };
+const connected: ConnectionState = {
+  status: "connected",
+  protocolVersion: "2025-06-18",
+};
 const disconnected: ConnectionState = { status: "disconnected" };
 const connecting: ConnectionState = { status: "connecting" };
 const failed: ConnectionState = {

clients/web/src/components/groups/ServerCard/ServerCard.test.tsx

@@ -21,7 +21,10 @@ const sseConfig: MCPServerConfig = {
   url: "https://api.example.com/sse",
 };
 
-const connected: ConnectionState = { status: "connected" };
+const connected: ConnectionState = {
+  status: "connected",
+  protocolVersion: "2025-06-18",
+};
 const disconnected: ConnectionState = { status: "disconnected" };
 const connecting: ConnectionState = { status: "connecting" };
 const errored: ConnectionState = {
@@ -149,6 +152,30 @@ describe("ServerCard", () => {
     expect(container.querySelector('[aria-disabled="true"]')).toBeNull();
   });
 
+  it("renders the negotiated protocol version when connected", () => {
+    renderWithMantine(<ServerCard {...baseProps} connection={connected} />);
+    expect(screen.getByText("MCP 2025-06-18")).toBeInTheDocument();
+  });
+
+  it("omits the protocol version when not connected", () => {
+    renderWithMantine(
+      <ServerCard
+        {...baseProps}
+        connection={{ status: "disconnected", protocolVersion: "2025-06-18" }}
+      />,
+    );
+    expect(screen.queryByText("MCP 2025-06-18")).not.toBeInTheDocument();
+  });
+
+  it("omits the protocol version when connected but none was negotiated", () => {
+    renderWithMantine(
+      <ServerCard {...baseProps} connection={{ status: "connected" }} />,
+    );
+    expect(
+      screen.queryByText(/^MCP \d{4}-\d{2}-\d{2}$/),
+    ).not.toBeInTheDocument();
+  });
+
   it("omits the version badge when info is missing", () => {
     renderWithMantine(<ServerCard {...baseProps} info={undefined} />);
     expect(screen.queryByText("1.2.0")).not.toBeInTheDocument();

clients/web/src/components/groups/ServerCard/ServerCard.tsx

@@ -49,6 +49,12 @@ const ModeText = Text.withProps({
   c: "dimmed",
 });
 
+const ProtocolText = Text.withProps({
+  size: "sm",
+  c: "dimmed",
+  ml: "auto",
+});
+
 const SubtleButton = Button.withProps({
   variant: "subtle",
   size: "xs",
@@ -102,6 +108,8 @@ export function ServerCard({
   const transport = getTransport(config);
   const commandOrUrl = getCommandOrUrl(config);
   const version = info?.version;
+  const protocolVersion =
+    connection.status === "connected" ? connection.protocolVersion : undefined;
 
   return (
     <Card
@@ -134,6 +142,9 @@ export function ServerCard({
               {version && <Badge variant="outline">{version}</Badge>}
               <TransportBadge transport={transport} />
               <ModeText>{TRANSPORT_DESCRIPTION[transport]}</ModeText>
+              {protocolVersion && (
+                <ProtocolText>MCP {protocolVersion}</ProtocolText>
+              )}
             </Group>
 
             <ContentViewer

clients/web/src/components/views/InspectorView/InspectorView.test.tsx

@@ -198,6 +198,61 @@ describe("InspectorView", () => {
     expect(screen.getByRole("switch")).toBeChecked();
   });
 
+  it("surfaces the negotiated protocol version on the active connected card", () => {
+    renderWithMantine(
+      <InspectorView
+        {...makeProps({
+          servers: [sampleServer],
+          activeServer: "alpha",
+          connectionStatus: "connected",
+          initializeResult: connectedInit,
+        })}
+      />,
+    );
+    // initializeResult.protocolVersion is spliced onto the active server's
+    // connection; ServerCard renders it as "MCP <version>".
+    expect(screen.getByText("MCP 2025-06-18")).toBeInTheDocument();
+  });
+
+  it("does not show a protocol version on the card while disconnected", () => {
+    renderWithMantine(
+      <InspectorView
+        {...makeProps({
+          servers: [sampleServer],
+          activeServer: "alpha",
+          connectionStatus: "disconnected",
+          initializeResult: undefined,
+        })}
+      />,
+    );
+    expect(
+      screen.queryByText(/^MCP \d{4}-\d{2}-\d{2}$/),
+    ).not.toBeInTheDocument();
+  });
+
+  it("keeps the connected surface and hides the label when the version is unknown", () => {
+    // App emits initializeResult with protocolVersion "" when the negotiated
+    // version is somehow absent — the connected header/modal must still render
+    // (gated on serverInfo, not the version), and the card label stays hidden.
+    renderWithMantine(
+      <InspectorView
+        {...makeProps({
+          servers: [sampleServer],
+          activeServer: "alpha",
+          connectionStatus: "connected",
+          initializeResult: { ...connectedInit, protocolVersion: "" },
+        })}
+      />,
+    );
+    // Connected: the card toggle is on (connected surface is alive).
+    expect(screen.getByRole("switch")).toBeChecked();
+    // ...but no "MCP <version>" label, since the version is empty. (The
+    // date-shaped matcher avoids matching the "MCP Inspector" header title.)
+    expect(
+      screen.queryByText(/^MCP \d{4}-\d{2}-\d{2}$/),
+    ).not.toBeInTheDocument();
+  });
+
   it("snaps activeTab back to Servers when connection drops", async () => {
     const { rerender } = renderWithMantine(
       <InspectorView

clients/web/src/components/views/InspectorView/InspectorView.tsx

@@ -485,9 +485,23 @@ export function InspectorView({
         if (s.id !== activeServer) {
           return { ...s, connection: { status: "disconnected" } };
         }
-        return { ...s, connection: { status: connectionStatus } };
+        return {
+          ...s,
+          connection: {
+            status: connectionStatus,
+            // Surface the negotiated protocol version on the active card.
+            // initializeResult carries it (App builds it from the
+            // InspectorClient handshake, #1324) and is only ever truthy when
+            // connected — it's derived from connectionStatus in the same memo
+            // — so its presence already implies a live connection. App uses ""
+            // for an unknown version, so only set the field when it's present.
+            ...(initializeResult?.protocolVersion
+              ? { protocolVersion: initializeResult.protocolVersion }
+              : {}),
+          },
+        };
       }),
-    [serversInput, activeServer, connectionStatus],
+    [serversInput, activeServer, connectionStatus, initializeResult],
   );
 
   return (

clients/web/src/test/core/mcp/messageTrackingTransport.test.ts

@@ -9,6 +9,8 @@ class FakeTransport implements Transport {
   onmessage?: (message: JSONRPCMessage) => void;
   onclose?: () => void;
   onerror?: (error: Error) => void;
+  // Optional on the SDK Transport interface; stdio omits it, HTTP defines it.
+  setProtocolVersion?: (version: string) => void;
   async start(): Promise<void> {}
   async send(message: JSONRPCMessage): Promise<void> {
     this.sent.push(message);
@@ -120,3 +122,32 @@ describe("MessageTrackingTransport.onmessage", () => {
     expect(handler).toHaveBeenCalledTimes(3);
   });
 });
+
+describe("MessageTrackingTransport.setProtocolVersion", () => {
+  it("captures the negotiated version and exposes it via protocolVersion", () => {
+    const { tracked } = makeTracked();
+    expect(tracked.protocolVersion).toBeUndefined();
+    tracked.setProtocolVersion("2025-06-18");
+    expect(tracked.protocolVersion).toBe("2025-06-18");
+  });
+
+  it("forwards to the base transport's setProtocolVersion when present", () => {
+    const base = new FakeTransport();
+    const baseSet = vi.fn();
+    // stdio-style transports omit setProtocolVersion; HTTP transports define
+    // it to stamp the version into later request headers — forward to those.
+    base.setProtocolVersion = baseSet;
+    const tracked = new MessageTrackingTransport(base, {});
+    tracked.setProtocolVersion("2025-06-18");
+    expect(baseSet).toHaveBeenCalledWith("2025-06-18");
+    expect(tracked.protocolVersion).toBe("2025-06-18");
+  });
+
+  it("captures even when the base transport has no setProtocolVersion", () => {
+    // FakeTransport (like stdio) has no setProtocolVersion — must not throw.
+    const { tracked, base } = makeTracked();
+    expect(base.setProtocolVersion).toBeUndefined();
+    expect(() => tracked.setProtocolVersion("2025-06-18")).not.toThrow();
+    expect(tracked.protocolVersion).toBe("2025-06-18");
+  });
+});

clients/web/src/test/core/react/useInspectorClient.test.tsx

@@ -19,12 +19,14 @@ describe("useInspectorClient", () => {
       capabilities: CAPABILITIES,
       serverInfo: SERVER_INFO,
       instructions: "hello",
+      protocolVersion: "2025-06-18",
     });
     const { result } = renderHook(() => useInspectorClient(client));
     expect(result.current.status).toBe("connected");
     expect(result.current.capabilities).toEqual(CAPABILITIES);
     expect(result.current.serverInfo).toEqual(SERVER_INFO);
     expect(result.current.instructions).toBe("hello");
+    expect(result.current.protocolVersion).toBe("2025-06-18");
     expect(result.current.appRendererClient).toBeNull();
   });
 
@@ -34,6 +36,7 @@ describe("useInspectorClient", () => {
     expect(result.current.capabilities).toBeUndefined();
     expect(result.current.serverInfo).toBeUndefined();
     expect(result.current.instructions).toBeUndefined();
+    expect(result.current.protocolVersion).toBeUndefined();
     expect(result.current.appRendererClient).toBeNull();
   });
 
@@ -64,6 +67,16 @@ describe("useInspectorClient", () => {
     expect(result.current.instructions).toBe("after");
   });
 
+  it("subscribes to protocolVersionChange and updates", () => {
+    const client = new FakeInspectorClient();
+    const { result } = renderHook(() => useInspectorClient(client));
+    expect(result.current.protocolVersion).toBeUndefined();
+    act(() => {
+      client.setProtocolVersion("2025-06-18");
+    });
+    expect(result.current.protocolVersion).toBe("2025-06-18");
+  });
+
   it("connect() and disconnect() proxy to the client and update status", async () => {
     const client = new FakeInspectorClient();
     const { result } = renderHook(() => useInspectorClient(client));

clients/web/src/test/integration/mcp/inspectorClient.test.ts

@@ -673,6 +673,28 @@ describe("InspectorClient", () => {
       expect(client.getServerInfo()).toBeDefined();
     });
 
+    it("exposes the negotiated protocol version after connect (stdio)", async () => {
+      client = new InspectorClient(
+        {
+          type: "stdio",
+          command: serverCommand.command,
+          args: serverCommand.args,
+        },
+        {
+          environment: { transport: createTransportNode },
+        },
+      );
+
+      expect(client.getProtocolVersion()).toBeUndefined();
+      await client.connect();
+      // stdio transports don't store the version themselves; the capture
+      // happens in MessageTrackingTransport, so this also guards that path.
+      expect(client.getProtocolVersion()).toMatch(/^\d{4}-\d{2}-\d{2}$/);
+
+      await client.disconnect();
+      expect(client.getProtocolVersion()).toBeUndefined();
+    });
+
     it("should not auto-fetch server contents when disabled", async () => {
       client = new InspectorClient(
         {