diff --git a/app.py b/app.py
index 8456717..5b99e20 100644
--- a/app.py
+++ b/app.py
@@ -1,7 +1,7 @@
 from pathlib import Path
 import json
 from typing import Tuple, Dict, List
-from flask import Flask, render_template, request
+from flask import Flask, render_template, request, send_from_directory
 
 app = Flask(__name__)
 
@@ -77,5 +77,16 @@ def index():
     )
 
 
+@app.route('/manifest.webmanifest')
+def manifest_file():
+    return send_from_directory(Path(__file__).parent / 'static', 'manifest.webmanifest', mimetype='application/manifest+json')
+
+
+@app.route('/sw.js')
+def service_worker():
+    # Service Worker muss auf Top-Level liegen
+    return send_from_directory(Path(__file__).parent / 'static', 'sw.js', mimetype='application/javascript')
+
+
 if __name__ == "__main__":
     app.run(debug=True)
diff --git a/static/manifest.webmanifest b/static/manifest.webmanifest
new file mode 100644
index 0000000..a46cbdf
--- /dev/null
+++ b/static/manifest.webmanifest
@@ -0,0 +1,18 @@
+{
+  "name": "Wordle‑Cheater",
+  "short_name": "W‑Cheater",
+  "description": "Hilft bei der Lösung deutschsprachiger Wordle‑Rätsel mit Positions- und Buchstabenfiltern.",
+  "start_url": "/",
+  "scope": "/",
+  "display": "standalone",
+  "background_color": "#0b1220",
+  "theme_color": "#0b1220",
+  "icons": [
+    {
+      "src": "/static/favicon.svg",
+      "sizes": "any",
+      "type": "image/svg+xml",
+      "purpose": "any maskable"
+    }
+  ]
+}
diff --git a/static/sw.js b/static/sw.js
new file mode 100644
index 0000000..577c368
--- /dev/null
+++ b/static/sw.js
@@ -0,0 +1,39 @@
+const CACHE_NAME = 'wordle-cheater-v1';
+const APP_SHELL = [
+  '/',
+  '/static/favicon.svg',
+];
+
+self.addEventListener('install', (event) => {
+  event.waitUntil(
+    caches.open(CACHE_NAME).then((cache) => cache.addAll(APP_SHELL))
+  );
+});
+
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    caches.keys().then((keys) => Promise.all(
+      keys.map((k) => (k === CACHE_NAME ? null : caches.delete(k)))
+    ))
+  );
+});
+
+self.addEventListener('fetch', (event) => {
+  const { request } = event;
+  // Netzwerk zuerst für HTML, sonst Cache-First
+  if (request.mode === 'navigate') {
+    event.respondWith(
+      fetch(request).catch(() => caches.match('/'))
+    );
+    return;
+  }
+  event.respondWith(
+    caches.match(request).then((cached) =>
+      cached || fetch(request).then((resp) => {
+        const copy = resp.clone();
+        caches.open(CACHE_NAME).then((cache) => cache.put(request, copy));
+        return resp;
+      })
+    )
+  );
+});
diff --git a/templates/index.html b/templates/index.html
index 2f6f65f..3e444b5 100644
--- a/templates/index.html
+++ b/templates/index.html
@@ -15,6 +15,8 @@
     <meta name="twitter:title" content="Wordle‑Cheater (DE)" />
     <meta name="twitter:description" content="Finde deutsche 5‑Buchstaben‑Wörter mit Positions- und Buchstabenfiltern. Quellen: OpenThesaurus & wordfreq." />
     <link rel="icon" type="image/svg+xml" href="{{ url_for('static', filename='favicon.svg') }}" />
+    <link rel="manifest" href="/manifest.webmanifest" />
+    <meta name="theme-color" content="#0b1220" />
     <meta name="color-scheme" content="light dark" />
     <script>
         (function() {
@@ -183,5 +185,12 @@
             });
         })();
     </script>
+    <script>
+        if ('serviceWorker' in navigator) {
+            window.addEventListener('load', function() {
+                navigator.serviceWorker.register('/sw.js');
+            });
+        }
+    </script>
 </body>
 </html>