diff --git a/src/App.tsx b/src/App.tsx
index bcbda826..93d7cfd5 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -9,7 +9,44 @@ import { PluginsProvider } from './contexts/PluginsContext';
 import AppContent from './components/app/AppContent';
 import i18n from './i18n/config.js';
 
+function detectRouterBasename() {
+  const explicitBasename = typeof window !== 'undefined' ? window.__ROUTER_BASENAME__ || '' : '';
+  if (explicitBasename) {
+    return explicitBasename.replace(/\/+$/, '');
+  }
+
+  if (typeof window === 'undefined' || typeof document === 'undefined') {
+    return '';
+  }
+
+  const candidatePaths = [
+    document.querySelector('link[rel="manifest"]')?.getAttribute('href'),
+    document.querySelector('script[type="module"][src]')?.getAttribute('src'),
+    document.querySelector('link[rel="icon"][href]')?.getAttribute('href'),
+  ].filter((value): value is string => Boolean(value));
+
+  let detectedBasename = '';
+  for (const candidate of candidatePaths) {
+    try {
+      const pathname = new URL(candidate, document.baseURI || window.location.href).pathname;
+      const match = pathname.match(/^(.*)\/(?:assets\/|manifest\.json$|favicon\.(?:svg|png)$)/);
+      if (match) {
+        const normalized = match[1] ? match[1].replace(/\/+$/, '') : '';
+        if (normalized.length > detectedBasename.length) {
+          detectedBasename = normalized;
+        }
+      }
+    } catch {
+      // Ignore invalid candidate URLs and continue checking other hints.
+    }
+  }
+
+  return detectedBasename;
+}
+
 export default function App() {
+  const routerBasename = detectRouterBasename();
+
   return (
     <I18nextProvider i18n={i18n}>
       <ThemeProvider>
@@ -19,7 +56,7 @@ export default function App() {
               <TasksSettingsProvider>
                 <TaskMasterProvider>
                 <ProtectedRoute>
-                  <Router basename={window.__ROUTER_BASENAME__ || ''}>
+                  <Router basename={routerBasename}>
                     <Routes>
                       <Route path="/" element={<AppContent />} />
                       <Route path="/session/:sessionId" element={<AppContent />} />