diff --git a/src/lib/db.js b/src/lib/db.js
new file mode 100644
index 0000000..9ea591a
--- /dev/null
+++ b/src/lib/db.js
@@ -0,0 +1,83 @@
+const DB_NAME = 'outlier-saver';
+const DB_VERSION = 1;
+
+let dbPromise = null;
+
+export function openDb() {
+  dbPromise ??= new Promise((resolve, reject) => {
+    const request = indexedDB.open(DB_NAME, DB_VERSION);
+    request.onupgradeneeded = () => {
+      const db = request.result;
+      db.createObjectStore('outliers', { keyPath: 'videoId' }).createIndex('updatedAt', 'updatedAt');
+      db.createObjectStore('channels', { keyPath: 'channelId' });
+      db.createObjectStore('seen', { keyPath: 'videoId' });
+    };
+    request.onsuccess = () => resolve(request.result);
+    request.onerror = () => reject(request.error);
+  }).catch((err) => {
+    dbPromise = null;
+    throw err;
+  });
+  return dbPromise;
+}
+
+function promisify(request) {
+  return new Promise((resolve, reject) => {
+    request.onsuccess = () => resolve(request.result);
+    request.onerror = () => reject(request.error);
+  });
+}
+
+async function getMany(storeName, keys) {
+  const db = await openDb();
+  const store = db.transaction(storeName, 'readonly').objectStore(storeName);
+  const records = await Promise.all(keys.map((key) => promisify(store.get(key))));
+  return new Map(records.filter(Boolean).map((record) => [record[store.keyPath], record]));
+}
+
+async function putMany(storeName, records) {
+  if (records.length === 0) return;
+  const db = await openDb();
+  await new Promise((resolve, reject) => {
+    const tx = db.transaction(storeName, 'readwrite');
+    const store = tx.objectStore(storeName);
+    for (const record of records) store.put(record);
+    tx.oncomplete = () => resolve();
+    tx.onerror = () => reject(tx.error);
+    tx.onabort = () => reject(tx.error);
+  });
+}
+
+export const getSeen = (videoIds) => getMany('seen', videoIds);
+export const putSeen = (records) => putMany('seen', records);
+export const getChannels = (channelIds) => getMany('channels', channelIds);
+export const putChannels = (records) => putMany('channels', records);
+export const getOutliers = (videoIds) => getMany('outliers', videoIds);
+export const putOutliers = (records) => putMany('outliers', records);
+
+export async function listOutliers(limit = Infinity) {
+  const db = await openDb();
+  return new Promise((resolve, reject) => {
+    const results = [];
+    const request = db
+      .transaction('outliers', 'readonly')
+      .objectStore('outliers')
+      .index('updatedAt')
+      .openCursor(null, 'prev');
+    request.onsuccess = () => {
+      const cursor = request.result;
+      if (!cursor || results.length >= limit) {
+        resolve(results);
+        return;
+      }
+      results.push(cursor.value);
+      cursor.continue();
+    };
+    request.onerror = () => reject(request.error);
+  });
+}
+
+export async function countOutliers() {
+  const db = await openDb();
+  return promisify(db.transaction('outliers', 'readonly').objectStore('outliers').count());
+}