diff --git a/manifest.json b/manifest.json
new file mode 100644
index 0000000..e74fdee
--- /dev/null
+++ b/manifest.json
@@ -0,0 +1,10 @@
+{
+  "manifest_version": 3,
+  "name": "Outlier Saver",
+  "version": "0.1.0",
+  "description": "Находит на YouTube видео с аномальными просмотрами и сохраняет их локально.",
+  "permissions": ["storage"],
+  "host_permissions": ["https://www.googleapis.com/youtube/v3/*"],
+  "background": { "service_worker": "src/background.js", "type": "module" },
+  "action": { "default_title": "Outlier Saver" }
+}
diff --git a/src/background.js b/src/background.js
new file mode 100644
index 0000000..671b872
--- /dev/null
+++ b/src/background.js
@@ -0,0 +1,136 @@
+import { ApiError, fetchChannels, fetchVideos, nextQuotaReset } from './lib/api.js';
+import * as db from './lib/db.js';
+import { processBatch } from './lib/process.js';
+import { getSettings, getStatus, setStatus } from './lib/storage.js';
+import { isVideoId } from './lib/video-id.js';
+
+const BATCH_SIZE = 50;
+const FLUSH_DELAY_MS = 1000;
+const MAX_QUEUE = 5000;
+const PAGES = new Set(['home', 'watch', 'search', 'channel']);
+
+// videoId -> queue item. In memory only: if the worker is killed, the content script
+// re-sends visible ids after the next navigation, and `seen` is written only after success.
+const queue = new Map();
+let flushTimer = null;
+let flushing = false;
+
+function sanitizeItem(raw) {
+  if (!raw || !isVideoId(raw.videoId)) return null;
+  return {
+    videoId: raw.videoId,
+    vidiqScore: typeof raw.vidiqScore === 'number' && Number.isFinite(raw.vidiqScore) ? raw.vidiqScore : null,
+    viaShortsUrl: raw.viaShortsUrl === true,
+    page: PAGES.has(raw.page) ? raw.page : 'home',
+  };
+}
+
+function enqueue(rawItems) {
+  for (const raw of rawItems) {
+    const item = sanitizeItem(raw);
+    if (!item) continue;
+    const queued = queue.get(item.videoId);
+    if (queued) {
+      queued.vidiqScore = item.vidiqScore ?? queued.vidiqScore;
+      queued.viaShortsUrl = queued.viaShortsUrl || item.viaShortsUrl;
+    } else if (queue.size < MAX_QUEUE) {
+      queue.set(item.videoId, item);
+    }
+  }
+  scheduleFlush();
+}
+
+function requeue(items) {
+  for (const item of items) if (!queue.has(item.videoId)) queue.set(item.videoId, item);
+}
+
+function takeBatch() {
+  const batch = [];
+  for (const [videoId, item] of queue) {
+    if (batch.length >= BATCH_SIZE) break;
+    batch.push(item);
+    queue.delete(videoId);
+  }
+  return batch;
+}
+
+function scheduleFlush() {
+  if (flushTimer !== null || flushing || queue.size === 0) return;
+  flushTimer = setTimeout(flush, FLUSH_DELAY_MS);
+}
+
+async function updateBadge(status) {
+  if (status.state === 'ok') {
+    await chrome.action.setBadgeText({ text: '' });
+    return;
+  }
+  await chrome.action.setBadgeBackgroundColor({ color: '#d93025' });
+  await chrome.action.setBadgeText({ text: '!' });
+}
+
+async function reportStatus(status) {
+  await setStatus(status);
+  await updateBadge(status);
+}
+
+// Returns true when the flush loop may continue, false when collection must stop.
+async function handleError(err, batch) {
+  if (err instanceof ApiError && err.kind === 'quota') {
+    requeue(batch);
+    await reportStatus({ state: 'quota', until: nextQuotaReset(), message: err.message });
+    return false;
+  }
+  if (err instanceof ApiError && err.kind === 'invalid-key') {
+    requeue(batch);
+    await reportStatus({ state: 'invalid-key', message: err.message });
+    return false;
+  }
+  console.warn(`Outlier Saver: dropped a batch of ${batch.length} ids`, err);
+  return true;
+}
+
+async function flush() {
+  flushTimer = null;
+  if (flushing) return;
+  flushing = true;
+  try {
+    while (queue.size > 0) {
+      const settings = await getSettings();
+      if (!settings.apiKey) {
+        await reportStatus({ state: 'no-key' });
+        return;
+      }
+      const status = await getStatus();
+      if (status.state === 'invalid-key') return;
+      if (status.state === 'quota' && Date.now() < status.until) return;
+      if (status.state !== 'ok') await reportStatus({ state: 'ok' });
+
+      const batch = takeBatch();
+      const apiKey = settings.apiKey;
+      const api = {
+        fetchVideos: (ids) => fetchVideos(ids, { apiKey }),
+        fetchChannels: (ids) => fetchChannels(ids, { apiKey }),
+      };
+      try {
+        await processBatch(batch, { settings, db, api });
+      } catch (err) {
+        if (!(await handleError(err, batch))) return;
+      }
+    }
+  } finally {
+    flushing = false;
+  }
+}
+
+chrome.runtime.onMessage.addListener((message) => {
+  if (message?.type === 'videos-seen' && Array.isArray(message.items)) enqueue(message.items);
+});
+
+// A new API key clears a previous "no key / invalid key / quota" pause.
+chrome.storage.onChanged.addListener((changes, area) => {
+  if (area !== 'local' || !changes.settings) return;
+  if (changes.settings.oldValue?.apiKey === changes.settings.newValue?.apiKey) return;
+  reportStatus({ state: 'ok' }).then(scheduleFlush);
+});
+
+getStatus().then(updateBadge);