diff --git a/src/service-worker.js b/src/service-worker.js
new file mode 100644
index 00000000..9fbf606c
--- /dev/null
+++ b/src/service-worker.js
@@ -0,0 +1,61 @@
+import { build, files, version } from '$service-worker';
+ 
+// Create a unique cache name for this deployment
+const CACHE = `cache-${version}`;
+ 
+const ASSETS = [
+  ...build, // the app itself
+  ...files  // everything in `static`
+];
+ 
+self.addEventListener('install', (event) => {
+  // Create a new cache and add all files to it
+  async function addFilesToCache() {
+    const cache = await caches.open(CACHE);
+    await cache.addAll(ASSETS);
+  }
+ 
+  event.waitUntil(addFilesToCache());
+});
+ 
+self.addEventListener('activate', (event) => {
+  // Remove previous cached data from disk
+  async function deleteOldCaches() {
+    for (const key of await caches.keys()) {
+      if (key !== CACHE) await caches.delete(key);
+    }
+  }
+ 
+  event.waitUntil(deleteOldCaches());
+});
+ 
+self.addEventListener('fetch', (event) => {
+  // ignore POST requests etc
+  if (event.request.method !== 'GET') return;
+ 
+  async function respond() {
+    const url = new URL(event.request.url);
+    const cache = await caches.open(CACHE);
+ 
+    // `build`/`files` can always be served from the cache
+    if (ASSETS.includes(url.pathname)) {
+      return cache.match(event.request);
+    }
+ 
+    // for everything else, try the network first, but
+    // fall back to the cache if we're offline
+    try {
+      const response = await fetch(event.request);
+ 
+      if (response.status === 200) {
+        cache.put(event.request, response.clone());
+      }
+ 
+      return response;
+    } catch {
+      return cache.match(event.request);
+    }
+  }
+ 
+  event.respondWith(respond());
+});
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