fix: use official ext-apps useApp hook to fix blank MCP App rendering (#578)

The custom useToolData hook had lifecycle issues that prevented the UI
from rendering in Claude Desktop/web: no appInfo in App constructor,
unhandled connect() Promise, app.close() on unmount conflicting with
React Strict Mode. Switched to the official useApp hook from
@modelcontextprotocol/ext-apps/react which handles initialization
handshake, handler registration, and cleanup correctly.

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [2.34.4] - 2026-02-07
+
+### Fixed
+
+- **MCP Apps: Fix blank UI rendering in Claude**: Rewrote `useToolData` hook to use the official `useApp` hook from `@modelcontextprotocol/ext-apps/react` instead of manually managing `App` lifecycle
+  - Proper initialization handshake with host via `appInfo` and `capabilities`
+  - Handlers registered via `onAppCreated` callback (before `connect()`) to avoid race conditions
+  - Removed `app.close()` on unmount which caused issues with React Strict Mode
+  - Added visible error and connection states with inline colors for debugging
+
+Conceived by Romuald Czlonkowski - https://www.aiadvisors.pl/en
+
 ## [2.34.3] - 2026-02-07
 
 ### Fixed

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.34.3",
+  "version": "2.34.4",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",

ui-apps/src/apps/operation-result/App.tsx

@@ -5,10 +5,18 @@ import { useToolData } from '@shared/hooks/useToolData';
 import type { OperationResultData } from '@shared/types';
 
 export default function App() {
-  const data = useToolData<OperationResultData>();
+  const { data, error, isConnected } = useToolData<OperationResultData>();
+
+  if (error) {
+    return <div style={{ padding: '16px', color: '#ef4444' }}>Error: {error}</div>;
+  }
+
+  if (!isConnected) {
+    return <div style={{ padding: '16px', color: '#9ca3af' }}>Connecting...</div>;
+  }
 
   if (!data) {
-    return <div style={{ padding: '16px', color: 'var(--n8n-text-muted)' }}>Loading...</div>;
+    return <div style={{ padding: '16px', color: '#9ca3af' }}>Waiting for data...</div>;
   }
 
   const isSuccess = data.status === 'success';

ui-apps/src/apps/validation-summary/App.tsx

@@ -5,10 +5,18 @@ import { useToolData } from '@shared/hooks/useToolData';
 import type { ValidationSummaryData } from '@shared/types';
 
 export default function App() {
-  const data = useToolData<ValidationSummaryData>();
+  const { data, error, isConnected } = useToolData<ValidationSummaryData>();
+
+  if (error) {
+    return <div style={{ padding: '16px', color: '#ef4444' }}>Error: {error}</div>;
+  }
+
+  if (!isConnected) {
+    return <div style={{ padding: '16px', color: '#9ca3af' }}>Connecting...</div>;
+  }
 
   if (!data) {
-    return <div style={{ padding: '16px', color: 'var(--n8n-text-muted)' }}>Loading...</div>;
+    return <div style={{ padding: '16px', color: '#9ca3af' }}>Waiting for data...</div>;
   }
 
   return (

ui-apps/src/shared/hooks/useToolData.ts

@@ -1,14 +1,17 @@
-import { useState, useEffect } from 'react';
-import { App } from '@modelcontextprotocol/ext-apps';
+import { useState, useCallback } from 'react';
+import { useApp } from '@modelcontextprotocol/ext-apps/react';
 
-export function useToolData<T>(): T | null {
+interface UseToolDataResult<T> {
+  data: T | null;
+  error: string | null;
+  isConnected: boolean;
+}
+
+export function useToolData<T>(): UseToolDataResult<T> {
   const [data, setData] = useState<T | null>(null);
 
-  useEffect(() => {
-    const app = new App();
-
+  const onAppCreated = useCallback((app: any) => {
     app.ontoolresult = (result: any) => {
-      // The host pushes tool result content; parse the first text item as JSON
       if (result?.content) {
         const textItem = Array.isArray(result.content)
           ? result.content.find((c: any) => c.type === 'text')
@@ -17,19 +20,22 @@ export function useToolData<T>(): T | null {
           try {
             setData(JSON.parse(textItem.text) as T);
           } catch {
-            // Not JSON — use raw text as-is
             setData(textItem.text as unknown as T);
           }
         }
       }
     };
-
-    app.connect();
-
-    return () => {
-      app.close();
-    };
   }, []);
 
-  return data;
+  const { isConnected, error } = useApp({
+    appInfo: { name: 'n8n-mcp-ui', version: '1.0.0' },
+    capabilities: {},
+    onAppCreated,
+  });
+
+  return {
+    data,
+    error: error?.message ?? null,
+    isConnected,
+  };
 }