Expose negotiated MCP protocol version

client/src/App.tsx

@@ -374,6 +374,7 @@ const App = () => {
   const {
     connectionStatus,
     serverCapabilities,
+    mcpProtocolVersion,
     serverImplementation,
     mcpClient,
     requestHistory,
@@ -1342,6 +1343,7 @@ const App = () => {
           connectionType={connectionType}
           setConnectionType={setConnectionType}
           serverImplementation={serverImplementation}
+          mcpProtocolVersion={mcpProtocolVersion}
         />
         <div
           onMouseDown={handleSidebarDragStart}

client/src/components/Sidebar.tsx

@@ -78,6 +78,7 @@ interface SidebarProps {
   serverImplementation?:
     | (WithIcons & { name?: string; version?: string; websiteUrl?: string })
     | null;
+  mcpProtocolVersion?: string | null;
 }
 
 const Sidebar = ({
@@ -110,6 +111,7 @@ const Sidebar = ({
   connectionType,
   setConnectionType,
   serverImplementation,
+  mcpProtocolVersion,
 }: SidebarProps) => {
   const [theme, setTheme] = useTheme();
   const [showEnvVars, setShowEnvVars] = useState(false);
@@ -847,6 +849,11 @@ const Sidebar = ({
                         Version: {serverImplementation.version}
                       </div>
                     )}
+                    {mcpProtocolVersion && (
+                      <div className="text-xs text-gray-500 dark:text-gray-400">
+                        Protocol: {mcpProtocolVersion}
+                      </div>
+                    )}
                   </div>
                 );
               })()}

client/src/lib/hooks/__tests__/useConnection.test.tsx

@@ -1213,6 +1213,34 @@ describe("useConnection", () => {
         mockStreamableHTTPTransport.options?.requestInit?.headers,
       ).toHaveProperty("X-MCP-Proxy-Auth", "Bearer test-proxy-token");
     });
+
+    test("exposes negotiated protocol version from response headers", async () => {
+      const response = {
+        headers: {
+          get: jest.fn((name: string) =>
+            name === "mcp-protocol-version" ? "2025-06-18" : null,
+          ),
+        },
+      } as unknown as Response;
+      (global.fetch as jest.Mock).mockResolvedValueOnce(response);
+
+      const { result } = renderHook(() =>
+        useConnection({
+          ...defaultProps,
+          connectionType: "direct",
+        }),
+      );
+
+      await act(async () => {
+        await result.current.connect();
+      });
+
+      await act(async () => {
+        await mockSSETransport.options?.fetch?.("http://localhost:8080");
+      });
+
+      expect(result.current.mcpProtocolVersion).toBe("2025-06-18");
+    });
   });
 
   describe("Custom Headers", () => {

client/src/lib/hooks/useConnection.ts

@@ -1200,6 +1200,7 @@ export function useConnection({
   return {
     connectionStatus,
     serverCapabilities,
+    mcpProtocolVersion,
     serverImplementation,
     mcpClient,
     requestHistory,