diff --git a/index.js b/index.js
index 15fa500..eec2615 100644
--- a/index.js
+++ b/index.js
@@ -969,6 +969,9 @@ export default class ActivityPubEndpoint {
     Indiekit.addCollection("ap_filters");
     Indiekit.addCollection("ap_filter_keywords");
 
+    // Plugin settings (single document, admin UI at /admin/settings)
+    Indiekit.addCollection("ap_settings");
+
     // Store collection references (posts resolved lazily)
     const indiekitCollections = Indiekit.collections;
     this._collections = {
diff --git a/lib/settings.js b/lib/settings.js
new file mode 100644
index 0000000..cd10693
--- /dev/null
+++ b/lib/settings.js
@@ -0,0 +1,72 @@
+/**
+ * Plugin settings — stored in ap_settings MongoDB collection.
+ *
+ * getSettings() merges DB values over hardcoded defaults.
+ * Consumers call this once per operation (or use cached middleware for hot paths).
+ */
+
+export const DEFAULTS = {
+  // Instance & Client API
+  instanceLanguages: ["en"],
+  maxCharacters: 5000,
+  maxMediaAttachments: 4,
+  defaultVisibility: "public",
+  defaultLanguage: "en",
+
+  // Federation & Delivery
+  timelineRetention: 1000,
+  notificationRetentionDays: 30,
+  activityRetentionDays: 90,
+  replyChainDepth: 5,
+  broadcastBatchSize: 25,
+  broadcastBatchDelay: 5000,
+  parallelWorkers: 5,
+  logLevel: "warning",
+
+  // Migration
+  refollowBatchSize: 10,
+  refollowDelay: 3000,
+  refollowBatchDelay: 30000,
+
+  // Security
+  refreshTokenTtlDays: 90,
+};
+
+/**
+ * Load settings from MongoDB, merged over defaults.
+ *
+ * @param {Map|object} collections - Indiekit collections map or plain object with ap_settings
+ * @returns {Promise<object>} Settings object with all keys guaranteed present
+ */
+export async function getSettings(collections) {
+  const col = collections?.get
+    ? collections.get("ap_settings")
+    : collections?.ap_settings;
+  if (!col) return { ...DEFAULTS };
+
+  try {
+    const doc = await col.findOne({});
+    return { ...DEFAULTS, ...(doc?.settings || {}) };
+  } catch {
+    return { ...DEFAULTS };
+  }
+}
+
+/**
+ * Save settings to MongoDB.
+ *
+ * @param {Map|object} collections - Indiekit collections map or plain object
+ * @param {object} settings - Settings object (all keys from DEFAULTS)
+ */
+export async function saveSettings(collections, settings) {
+  const col = collections?.get
+    ? collections.get("ap_settings")
+    : collections?.ap_settings;
+  if (!col) return;
+
+  await col.updateOne(
+    {},
+    { $set: { settings, updatedAt: new Date().toISOString() } },
+    { upsert: true },
+  );
+}