diff --git a/package-lock.json b/package-lock.json
index a8cb3ec..12a3d69 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -19,6 +19,7 @@
         "@vue/eslint-config-typescript": "^14.1.3",
         "eslint": "^9.15.0",
         "eslint-plugin-vue": "^9.31.0",
+        "fake-indexeddb": "^6.2.5",
         "jsdom": "^25.0.1",
         "prettier": "^3.3.3",
         "typescript": "~5.6.3",
@@ -2885,6 +2886,16 @@
         "node": ">=12.0.0"
       }
     },
+    "node_modules/fake-indexeddb": {
+      "version": "6.2.5",
+      "resolved": "https://registry.npmjs.org/fake-indexeddb/-/fake-indexeddb-6.2.5.tgz",
+      "integrity": "sha512-CGnyrvbhPlWYMngksqrSSUT1BAVP49dZocrHuK0SvtR0D5TMs5wP0o3j7jexDJW01KSadjBp1M/71o/KR3nD1w==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "engines": {
+        "node": ">=18"
+      }
+    },
     "node_modules/fast-deep-equal": {
       "version": "3.1.3",
       "resolved": "https://registry.npmjs.org/fast-deep-equal/-/fast-deep-equal-3.1.3.tgz",
diff --git a/package.json b/package.json
index c0bd151..6b69fa4 100644
--- a/package.json
+++ b/package.json
@@ -26,6 +26,7 @@
     "@vue/eslint-config-typescript": "^14.1.3",
     "eslint": "^9.15.0",
     "eslint-plugin-vue": "^9.31.0",
+    "fake-indexeddb": "^6.2.5",
     "jsdom": "^25.0.1",
     "prettier": "^3.3.3",
     "typescript": "~5.6.3",
diff --git a/src/components/AppToolbar.vue b/src/components/AppToolbar.vue
index aae8dd6..99d5f17 100644
--- a/src/components/AppToolbar.vue
+++ b/src/components/AppToolbar.vue
@@ -7,6 +7,9 @@ import BaseModal from './BaseModal.vue';
 import CustomFunctionsModal from './CustomFunctionsModal.vue';
 import NamedRangesModal from './NamedRangesModal.vue';
 import MacrosModal from './MacrosModal.vue';
+import DocumentsModal from './DocumentsModal.vue';
+import { useLibrary } from '../store/library';
+import { parseDocument } from '../io/json';
 import TheLogo from './TheLogo.vue';
 import ToolbarIcon, { type ToolbarIconName } from './ToolbarIcon.vue';
 import { WICOM, WICOM_SOCIAL } from '../config/brand';
@@ -28,6 +31,7 @@ import {
 import type { Delimiter } from '../io/csv';
 
 const store = useDocument();
+const library = useLibrary();
 const { mode: themeMode, cycle: cycleTheme } = useTheme();
 const toasts = useToasts();
 
@@ -105,6 +109,17 @@ const aboutOpen = ref(false);
 const functionsOpen = ref(false);
 const namedRangesOpen = ref(false);
 const macrosOpen = ref(false);
+const documentsOpen = ref(false);
+
+// ---- document title (inline rename) ------------------------------------
+const titleDraft = ref(library.currentTitle.value);
+watch(library.currentTitle, (t) => (titleDraft.value = t));
+function commitTitle() {
+  const id = library.state.currentId;
+  const t = titleDraft.value.trim();
+  if (!id || !t) titleDraft.value = library.currentTitle.value;
+  else if (t !== library.currentTitle.value) void library.rename(id, t);
+}
 const busy = ref(false);
 const fileInput = ref<HTMLInputElement | null>(null);
 
@@ -157,7 +172,7 @@ function runCsvExport() {
 }
 async function runNumExport() {
   try {
-    await exportNum(store);
+    await exportNum(store, library.currentTitle.value);
     toasts.success('Dokument als .num gespeichert.');
   } catch (err) {
     toasts.error(`Speichern fehlgeschlagen: ${(err as Error).message}`);
@@ -165,13 +180,13 @@ async function runNumExport() {
 }
 
 function runJsonExport() {
-  exportJson(store);
+  exportJson(store, library.currentTitle.value);
   toasts.success('Dokument als JSON exportiert.');
 }
 async function runXlsxExport() {
   busy.value = true;
   try {
-    await exportXlsx(store);
+    await exportXlsx(store, library.currentTitle.value);
     toasts.success('Arbeitsmappe als XLSX exportiert.');
   } catch (err) {
     toasts.error(`XLSX-Export fehlgeschlagen: ${(err as Error).message}`);
@@ -247,13 +262,15 @@ async function handleFile(file: File) {
 
 defineExpose({ handleFile });
 
-async function doImport(action: 'replace' | 'append' | 'confirm') {
+async function doImport(action: 'new' | 'replace' | 'append' | 'confirm') {
   const ctx = importCtx.value;
   if (!ctx) return;
   busy.value = true;
   try {
     if (ctx.kind === 'json') {
-      if (action === 'replace') {
+      if (action === 'new') {
+        await library.create(parseDocument(ctx.text), ctx.fileName.replace(/\.(num|json)$/i, ''));
+      } else if (action === 'replace') {
         if (!confirm('Aktuelles Dokument vollständig ersetzen?')) return;
         importJsonReplace(store, ctx.text);
       } else {
@@ -279,18 +296,14 @@ async function doImport(action: 'replace' | 'append' | 'confirm') {
   }
 }
 
-function onNew() {
-  if (confirm('Neues, leeres Dokument anlegen? Alle Änderungen gehen verloren.')) {
-    store.newDocument();
-    toasts.info('Neues Dokument angelegt.');
-  }
+async function onNew() {
+  await library.createBlank();
+  toasts.info('Neues Dokument angelegt.');
 }
 
-function onSample() {
-  if (confirm('Musterdokument laden? Alle Änderungen gehen verloren.')) {
-    store.resetToSeed();
-    toasts.info('Musterdokument geladen.');
-  }
+async function onSample() {
+  await library.createSample();
+  toasts.info('Musterdokument als neues Dokument angelegt.');
 }
 </script>
 
@@ -303,6 +316,17 @@ function onSample() {
         <button class="by" type="button" @click="aboutOpen = true">wicom</button>
       </span>
     </div>
+    <input
+      v-model="titleDraft"
+      class="doc-title"
+      type="text"
+      title="Dokumentname (klicken zum Umbenennen)"
+      aria-label="Dokumentname"
+      :size="Math.max(8, Math.min(28, titleDraft.length + 1))"
+      @keydown.enter.prevent="($event.target as HTMLInputElement).blur()"
+      @keydown.esc.prevent="titleDraft = library.currentTitle.value; ($event.target as HTMLInputElement).blur()"
+      @blur="commitTitle()"
+    />
     <button
       class="gear"
       :class="{ on: store.ui.settingsOpen }"
@@ -381,7 +405,8 @@ function onSample() {
     <div ref="fileMenuWrap" class="menu-wrap">
       <button class="btn" @click="fileMenuOpen = !fileMenuOpen">Datei ▾</button>
       <ul v-if="fileMenuOpen" class="menu" @click="fileMenuOpen = false">
-        <li><button @click="onNew">Neu</button></li>
+        <li><button @click="documentsOpen = true">Dokumente …</button></li>
+        <li><button @click="onNew">Neues Dokument</button></li>
         <li><button @click="onSample">Muster · Umsatzanalyse</button></li>
         <li class="sep" />
         <li><button @click="pickFile">Öffnen / Importieren … (.num .json .csv .xlsx)</button></li>
@@ -433,7 +458,7 @@ function onSample() {
     @close="importOpen = false"
   >
     <template v-if="importCtx?.kind === 'json'">
-      <p>JSON-Dokument erkannt. Wie einfügen?</p>
+      <p>Dokument erkannt. Als eigenes Dokument öffnen oder in das aktuelle übernehmen?</p>
     </template>
 
     <template v-else-if="importCtx?.kind === 'csv'">
@@ -471,7 +496,8 @@ function onSample() {
       <button @click="importOpen = false">Abbrechen</button>
       <template v-if="importCtx?.kind === 'json'">
         <button @click="doImport('append')">Anhängen</button>
-        <button class="primary" @click="doImport('replace')">Ersetzen</button>
+        <button @click="doImport('replace')">Ersetzen</button>
+        <button class="primary" @click="doImport('new')">Als neues Dokument</button>
       </template>
       <button v-else class="primary" :disabled="busy" @click="doImport('confirm')">Importieren</button>
     </template>
@@ -481,6 +507,7 @@ function onSample() {
   <CustomFunctionsModal :open="functionsOpen" @close="functionsOpen = false" />
   <NamedRangesModal :open="namedRangesOpen" @close="namedRangesOpen = false" />
   <MacrosModal :open="macrosOpen" @close="macrosOpen = false" />
+  <DocumentsModal :open="documentsOpen" @close="documentsOpen = false" />
 
   <!-- Über / Impressum -->
   <BaseModal :open="aboutOpen" title="Über Numolus" @close="aboutOpen = false">
@@ -634,6 +661,27 @@ function onSample() {
 .btn-link:hover {
   color: var(--accent);
 }
+.doc-title {
+  min-width: 0;
+  max-width: 240px;
+  border: 1px solid transparent;
+  border-radius: 7px;
+  background: transparent;
+  padding: 4px 7px;
+  font: inherit;
+  font-size: 13.5px;
+  font-weight: 600;
+  color: var(--text);
+  text-overflow: ellipsis;
+}
+.doc-title:hover {
+  border-color: var(--border);
+}
+.doc-title:focus {
+  outline: none;
+  border-color: var(--accent);
+  background: var(--surface-2);
+}
 .gear {
   display: inline-flex;
   align-items: center;
diff --git a/src/components/DocumentsModal.vue b/src/components/DocumentsModal.vue
new file mode 100644
index 0000000..b954639
--- /dev/null
+++ b/src/components/DocumentsModal.vue
@@ -0,0 +1,211 @@
+<script setup lang="ts">
+/**
+ * "Dokumente" -- every document stored in this browser (IndexedDB, see
+ * src/store/library.ts): open, rename, duplicate, delete, create. The open
+ * document is marked; opening another one switches in place (and pushes a
+ * history entry, so the browser's back button returns to the previous one).
+ */
+import { nextTick, ref, watch } from 'vue';
+import { useLibrary } from '../store/library';
+import type { DocMeta } from '../io/library';
+import BaseModal from './BaseModal.vue';
+
+const props = defineProps<{ open: boolean }>();
+const emit = defineEmits<{ (e: 'close'): void }>();
+
+const library = useLibrary();
+
+const renamingId = ref<string | null>(null);
+const renameValue = ref('');
+const renameInput = ref<HTMLInputElement[] | null>(null);
+
+watch(
+  () => props.open,
+  (o) => {
+    if (o) renamingId.value = null;
+  },
+);
+
+const fmt = new Intl.DateTimeFormat('de-CH', { dateStyle: 'medium', timeStyle: 'short' });
+function when(ms: number): string {
+  const diff = Date.now() - ms;
+  if (diff < 60_000) return 'gerade eben';
+  if (diff < 3_600_000) return `vor ${Math.floor(diff / 60_000)} Min.`;
+  return fmt.format(ms);
+}
+
+async function openDoc(d: DocMeta) {
+  if (renamingId.value) return;
+  await library.open(d.id);
+  emit('close');
+}
+async function startRename(d: DocMeta) {
+  renamingId.value = d.id;
+  renameValue.value = d.title;
+  await nextTick();
+  renameInput.value?.[0]?.select();
+}
+async function commitRename() {
+  const id = renamingId.value;
+  renamingId.value = null;
+  if (id) await library.rename(id, renameValue.value);
+}
+async function remove(d: DocMeta) {
+  if (!confirm(`„${d.title}" endgültig löschen?`)) return;
+  await library.remove(d.id);
+}
+async function createNew() {
+  await library.createBlank();
+  emit('close');
+}
+</script>
+
+<template>
+  <BaseModal :open="open" title="Dokumente" wide @close="emit('close')">
+    <p v-if="!library.state.available" class="hint">
+      In diesem Browser können keine Dokumente gespeichert werden (IndexedDB nicht verfügbar,
+      z. B. im privaten Modus).
+    </p>
+    <ul v-else class="doc-list">
+      <li
+        v-for="d in library.state.docs"
+        :key="d.id"
+        class="doc-row"
+        :class="{ current: d.id === library.state.currentId }"
+      >
+        <input
+          v-if="renamingId === d.id"
+          ref="renameInput"
+          v-model="renameValue"
+          class="rename"
+          type="text"
+          @keydown.enter.prevent="commitRename"
+          @keydown.esc.stop.prevent="renamingId = null"
+          @blur="commitRename"
+        />
+        <button v-else class="doc-open" :title="`${d.title} öffnen`" @click="openDoc(d)">
+          <span class="doc-title">{{ d.title }}</span>
+          <span class="doc-when">{{ d.id === library.state.currentId ? 'geöffnet · ' : '' }}{{ when(d.updatedAt) }}</span>
+        </button>
+        <span class="doc-actions">
+          <button class="mini" @click="startRename(d)">Umbenennen</button>
+          <button class="mini" @click="library.duplicate(d.id)">Duplizieren</button>
+          <button class="mini danger" @click="remove(d)">Löschen</button>
+        </span>
+      </li>
+    </ul>
+    <p class="hint">
+      Dokumente werden nur in diesem Browser gespeichert. Zum Sichern oder Weitergeben:
+      Datei › Speichern (.num).
+    </p>
+
+    <template #footer>
+      <button @click="emit('close')">Schließen</button>
+      <button class="primary" :disabled="!library.state.available" @click="createNew">＋ Neues Dokument</button>
+    </template>
+  </BaseModal>
+</template>
+
+<style scoped>
+.hint {
+  color: var(--text-dim);
+  font-size: 12.5px;
+  line-height: 1.5;
+  margin: 12px 0 0;
+}
+.doc-list {
+  list-style: none;
+  margin: 0;
+  padding: 0;
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+  max-height: min(60vh, 480px);
+  overflow-y: auto;
+}
+.doc-row {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  padding: 4px 8px 4px 4px;
+  border-radius: 6px;
+  background: var(--surface-2);
+  border: 1px solid transparent;
+}
+.doc-row.current {
+  border-color: var(--accent);
+}
+.doc-open {
+  flex: 1;
+  min-width: 0;
+  display: flex;
+  flex-direction: column;
+  align-items: flex-start;
+  gap: 1px;
+  border: 0;
+  background: transparent;
+  padding: 4px 6px;
+  border-radius: 5px;
+  font: inherit;
+  color: var(--text);
+  text-align: left;
+  cursor: pointer;
+}
+.doc-open:hover .doc-title {
+  color: var(--accent);
+}
+.doc-title {
+  font-size: 13px;
+  font-weight: 600;
+  max-width: 100%;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+.doc-when {
+  font-size: 11.5px;
+  color: var(--text-dim);
+}
+.rename {
+  flex: 1;
+  min-width: 0;
+  border: 1px solid var(--accent);
+  border-radius: 6px;
+  padding: 5px 8px;
+  font: inherit;
+  font-size: 13px;
+  background: var(--surface);
+  color: var(--text);
+}
+.doc-actions {
+  display: flex;
+  gap: 6px;
+  flex: none;
+}
+@media (max-width: 560px) {
+  .doc-row {
+    flex-wrap: wrap;
+  }
+  .doc-actions {
+    width: 100%;
+    justify-content: flex-end;
+  }
+}
+.mini {
+  border: 1px solid var(--border);
+  background: var(--surface);
+  border-radius: 6px;
+  padding: 3px 9px;
+  font-size: 12px;
+  cursor: pointer;
+  color: var(--text);
+}
+.mini:hover {
+  border-color: var(--accent);
+  color: var(--accent);
+}
+.mini.danger:hover {
+  border-color: #dc2626;
+  color: #dc2626;
+}
+</style>
diff --git a/src/io/__tests__/library.spec.ts b/src/io/__tests__/library.spec.ts
new file mode 100644
index 0000000..4fd6ae8
--- /dev/null
+++ b/src/io/__tests__/library.spec.ts
@@ -0,0 +1,64 @@
+import { describe, expect, it } from 'vitest';
+import { IDBFactory } from 'fake-indexeddb';
+import { DocumentLibrary, newDocId, type DocMeta } from '../library';
+
+const meta = (id: string, title: string, updatedAt: number): DocMeta => ({
+  id,
+  title,
+  createdAt: 1,
+  updatedAt,
+});
+
+/** a fresh, empty in-memory IndexedDB per test */
+const openLib = () => DocumentLibrary.open(new IDBFactory());
+
+describe('DocumentLibrary', () => {
+  it('stores meta and content separately and reads them back', async () => {
+    const lib = await openLib();
+    await lib.put(meta('a', 'Budget', 10), '{"x":1}');
+    expect(await lib.getMeta('a')).toEqual(meta('a', 'Budget', 10));
+    expect(await lib.getContent('a')).toBe('{"x":1}');
+    expect(await lib.getContent('missing')).toBeUndefined();
+  });
+
+  it('lists documents most recently changed first', async () => {
+    const lib = await openLib();
+    await lib.put(meta('old', 'Alt', 10), '{}');
+    await lib.put(meta('new', 'Neu', 30), '{}');
+    await lib.put(meta('mid', 'Mitte', 20), '{}');
+    expect((await lib.list()).map((d) => d.id)).toEqual(['new', 'mid', 'old']);
+  });
+
+  it('patchMeta renames without touching content; unknown ids are ignored', async () => {
+    const lib = await openLib();
+    await lib.put(meta('a', 'Alt', 10), '{"keep":true}');
+    await lib.patchMeta('a', { title: 'Neu' });
+    await lib.patchMeta('nope', { title: 'X' });
+    expect((await lib.getMeta('a'))?.title).toBe('Neu');
+    expect(await lib.getContent('a')).toBe('{"keep":true}');
+    expect(await lib.list()).toHaveLength(1);
+  });
+
+  it('remove deletes meta and content', async () => {
+    const lib = await openLib();
+    await lib.put(meta('a', 'A', 10), '{}');
+    await lib.remove('a');
+    expect(await lib.getMeta('a')).toBeUndefined();
+    expect(await lib.getContent('a')).toBeUndefined();
+    expect(await lib.list()).toEqual([]);
+  });
+
+  it('keeps data across re-opening the same database', async () => {
+    const factory = new IDBFactory();
+    await (await DocumentLibrary.open(factory)).put(meta('a', 'A', 10), '{"v":2}');
+    expect(await (await DocumentLibrary.open(factory)).getContent('a')).toBe('{"v":2}');
+  });
+});
+
+describe('newDocId', () => {
+  it('produces distinct v4 UUIDs', () => {
+    const a = newDocId();
+    expect(a).toMatch(/^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/);
+    expect(newDocId()).not.toBe(a);
+  });
+});
diff --git a/src/io/library.ts b/src/io/library.ts
new file mode 100644
index 0000000..376869c
--- /dev/null
+++ b/src/io/library.ts
@@ -0,0 +1,113 @@
+/**
+ * The browser's document library: every numolus document the user has in
+ * this browser, stored in IndexedDB. Two object stores, so listing documents
+ * never has to read their (possibly large) contents:
+ *
+ *   meta     { id, title, createdAt, updatedAt }   -- the document list
+ *   content  { id, json }                          -- the document itself
+ *
+ * `json` is the serialised DocumentState (the same JSON a .num file holds).
+ * Plain promise wrapper over the IndexedDB API, no library; `factory` is
+ * injectable so tests can run against an in-memory implementation.
+ */
+
+export interface DocMeta {
+  id: string;
+  title: string;
+  /** epoch ms */
+  createdAt: number;
+  /** epoch ms of the last *content* change (not cursor moves) */
+  updatedAt: number;
+}
+
+interface ContentRecord {
+  id: string;
+  json: string;
+}
+
+const DB_NAME = 'numolus';
+const DB_VERSION = 1;
+
+function req<T>(r: IDBRequest<T>): Promise<T> {
+  return new Promise((resolve, reject) => {
+    r.onsuccess = () => resolve(r.result);
+    r.onerror = () => reject(r.error);
+  });
+}
+
+function done(tx: IDBTransaction): Promise<void> {
+  return new Promise((resolve, reject) => {
+    tx.oncomplete = () => resolve();
+    tx.onerror = () => reject(tx.error);
+    tx.onabort = () => reject(tx.error ?? new Error('Transaktion abgebrochen.'));
+  });
+}
+
+export class DocumentLibrary {
+  private constructor(private db: IDBDatabase) {}
+
+  static async open(factory: IDBFactory = indexedDB): Promise<DocumentLibrary> {
+    const r = factory.open(DB_NAME, DB_VERSION);
+    r.onupgradeneeded = () => {
+      const db = r.result;
+      if (!db.objectStoreNames.contains('meta')) db.createObjectStore('meta', { keyPath: 'id' });
+      if (!db.objectStoreNames.contains('content')) db.createObjectStore('content', { keyPath: 'id' });
+    };
+    const db = await req(r);
+    // another tab upgrading the schema later must not be blocked by us
+    db.onversionchange = () => db.close();
+    return new DocumentLibrary(db);
+  }
+
+  /** All documents, most recently changed first. */
+  async list(): Promise<DocMeta[]> {
+    const tx = this.db.transaction('meta', 'readonly');
+    const all = await req(tx.objectStore('meta').getAll() as IDBRequest<DocMeta[]>);
+    return all.sort((a, b) => b.updatedAt - a.updatedAt);
+  }
+
+  async getMeta(id: string): Promise<DocMeta | undefined> {
+    const tx = this.db.transaction('meta', 'readonly');
+    return req(tx.objectStore('meta').get(id) as IDBRequest<DocMeta | undefined>);
+  }
+
+  async getContent(id: string): Promise<string | undefined> {
+    const tx = this.db.transaction('content', 'readonly');
+    const rec = await req(tx.objectStore('content').get(id) as IDBRequest<ContentRecord | undefined>);
+    return rec?.json;
+  }
+
+  /** Create or overwrite a document -- meta and content in one transaction. */
+  async put(meta: DocMeta, json: string): Promise<void> {
+    const tx = this.db.transaction(['meta', 'content'], 'readwrite');
+    tx.objectStore('meta').put(meta);
+    tx.objectStore('content').put({ id: meta.id, json } satisfies ContentRecord);
+    await done(tx);
+  }
+
+  /** Update only the listing data (rename). No-op for an unknown id. */
+  async patchMeta(id: string, patch: Partial<Omit<DocMeta, 'id'>>): Promise<void> {
+    const tx = this.db.transaction('meta', 'readwrite');
+    const store = tx.objectStore('meta');
+    const cur = await req(store.get(id) as IDBRequest<DocMeta | undefined>);
+    if (cur) store.put({ ...cur, ...patch, id });
+    await done(tx);
+  }
+
+  async remove(id: string): Promise<void> {
+    const tx = this.db.transaction(['meta', 'content'], 'readwrite');
+    tx.objectStore('meta').delete(id);
+    tx.objectStore('content').delete(id);
+    await done(tx);
+  }
+}
+
+export function newDocId(): string {
+  // randomUUID exists only in secure contexts (https, localhost)
+  if (typeof crypto.randomUUID === 'function') return crypto.randomUUID();
+  const b = crypto.getRandomValues(new Uint8Array(16));
+  b[6] = (b[6] & 0x0f) | 0x40;
+  b[8] = (b[8] & 0x3f) | 0x80;
+  const h = Array.from(b, (x) => x.toString(16).padStart(2, '0')).join('');
+  return `${h.slice(0, 8)}-${h.slice(8, 12)}-${h.slice(12, 16)}-${h.slice(16, 20)}-${h.slice(20)}`;
+}
diff --git a/src/io/operations.ts b/src/io/operations.ts
index 7e6055b..f01998f 100644
--- a/src/io/operations.ts
+++ b/src/io/operations.ts
@@ -44,16 +44,21 @@ const breathe = () => new Promise((r) => setTimeout(r, 0));
 
 // ---- export ---------------------------------------------------------
 
-export function exportJson(store: DocumentStore): void {
-  downloadText('dokument.json', serializeDocument(store.snapshot()), 'application/json');
+/** A document title as a file name (without extension). */
+export function fileBaseName(title: string): string {
+  return title.replace(/[\\/:*?"<>|\u0000-\u001f]+/g, '-').trim() || 'dokument';
+}
+
+export function exportJson(store: DocumentStore, name = 'dokument'): void {
+  downloadText(`${fileBaseName(name)}.json`, serializeDocument(store.snapshot()), 'application/json');
 }
 
 /** Save as the native `.num` file (the JSON document, zipped -- see num.ts).
  *  The zip code loads on first use, like the xlsx support. */
-export async function exportNum(store: DocumentStore): Promise<void> {
+export async function exportNum(store: DocumentStore, name = 'dokument'): Promise<void> {
   const { packNum, NUM_MIMETYPE } = await import('./num');
   const bytes = packNum(serializeDocument(store.snapshot()));
-  downloadBlob('dokument.num', new Blob([bytes], { type: NUM_MIMETYPE }));
+  downloadBlob(`${fileBaseName(name)}.num`, new Blob([bytes], { type: NUM_MIMETYPE }));
 }
 
 /** The document JSON inside a `.num` file -- then imported like a `.json`. */
@@ -68,8 +73,8 @@ export function exportActiveTableCsv(store: DocumentStore, opts: CsvExportOption
   downloadText(`${table.name}.csv`, tableToCsv(store, table.id, opts), 'text/csv;charset=utf-8');
 }
 
-export async function exportXlsx(store: DocumentStore): Promise<void> {
-  downloadBlob('arbeitsmappe.xlsx', await documentToXlsx(store));
+export async function exportXlsx(store: DocumentStore, name = 'arbeitsmappe'): Promise<void> {
+  downloadBlob(`${fileBaseName(name)}.xlsx`, await documentToXlsx(store));
 }
 
 // ---- import: JSON ------------------------------------------------
diff --git a/src/main.ts b/src/main.ts
index 2680e10..851849b 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1,5 +1,10 @@
 import { createApp } from 'vue';
 import App from './App.vue';
+import { useLibrary } from './store/library';
 import './styles/main.css';
 
-createApp(App).mount('#app');
+// open the document (from IndexedDB) before the first render, so the app
+// never flashes an empty document first
+void useLibrary()
+  .init()
+  .finally(() => createApp(App).mount('#app'));
diff --git a/src/store/document.ts b/src/store/document.ts
index a12cf04..44a9ce3 100644
--- a/src/store/document.ts
+++ b/src/store/document.ts
@@ -81,11 +81,29 @@ import type {
 } from './types';
 import { defaultTableView, DEFAULT_ROW_H, MIN_GRID_SIZE, MAX_GRID_SIZE } from './types';
 import { createBlankDocument, createSeedDocument } from '../data/seed';
-import { validateDocument } from '../io/json';
 
-const STORAGE_KEY = 'numolus:doc:v2';
-/** Key used before the rename to numolus -- still read as a fallback. */
-const LEGACY_STORAGE_KEY = 'numbers-study:doc:v2';
+/** Where the document is persisted. Set by the document library
+ *  (src/store/library.ts) to write into IndexedDB; unset (tests, or before
+ *  the library has started) nothing is persisted. Called debounced with the
+ *  live reactive document -- the handler serialises it itself. */
+let persistHandler: ((doc: DocumentState) => void) | null = null;
+export function setPersistHandler(fn: ((doc: DocumentState) => void) | null) {
+  persistHandler = fn;
+}
+
+/** The part of a document that is *content* -- everything but the per-view
+ *  state (selection, active sheet/object). Used by undo history to tell an
+ *  edit from a mere cursor move, and by the library for the same distinction
+ *  when deciding whether a save changed anything other tabs care about. */
+export const contentFingerprint = (d: DocumentState) =>
+  JSON.stringify({
+    sheets: d.sheets,
+    locale: d.locale,
+    csvDelimiter: d.csvDelimiter,
+    customFunctions: d.customFunctions,
+    namedRanges: d.namedRanges,
+    macros: d.macros,
+  });
 
 const CASCADE = 28; // px offset for successive inserted objects
 
@@ -590,18 +608,9 @@ function rewriteRefsForRename(
   return '=' + out;
 }
 
+/** A blank document until the library (src/store/library.ts) loads the real
+ *  one from IndexedDB via replaceDocument() -- see main.ts. */
 function loadInitial(): DocumentState {
-  try {
-    const raw =
-      localStorage.getItem(STORAGE_KEY) ?? localStorage.getItem(LEGACY_STORAGE_KEY);
-    if (raw) {
-      // validateDocument migrates v1, validates + *normalises* v2 (fills in
-      // `view` and other defaults for documents saved by an older build).
-      return validateDocument(JSON.parse(raw));
-    }
-  } catch {
-    /* missing / corrupt / stale-schema -> clean fallback */
-  }
   return createBlankDocument();
 }
 
@@ -654,13 +663,22 @@ function createStore() {
   let persistTimer: ReturnType<typeof setTimeout> | undefined;
   function scheduleSave() {
     clearTimeout(persistTimer);
-    persistTimer = setTimeout(() => {
-      try {
-        localStorage.setItem(STORAGE_KEY, JSON.stringify(doc));
-      } catch {
-        /* quota / privacy mode -- ignore */
-      }
-    }, 250);
+    persistTimer = setTimeout(flushSave, 250);
+  }
+  /** Write a pending save right now (page hidden, switching documents). */
+  function flushSave() {
+    if (persistTimer === undefined) return;
+    clearTimeout(persistTimer);
+    persistTimer = undefined;
+    persistHandler?.(doc);
+  }
+  /** A change made here that hasn't been handed to persistence yet. */
+  const hasPendingSave = () => persistTimer !== undefined;
+  /** Drop a pending save -- the document was just loaded from where it
+   *  would be saved to. */
+  function cancelSave() {
+    clearTimeout(persistTimer);
+    persistTimer = undefined;
   }
 
   // ---- undo / redo (debounced content snapshots) -----------------------
@@ -686,15 +704,6 @@ function createStore() {
   const MAX_HISTORY = 100;
   const undoStack: DocumentState[] = [];
   const redoStack: DocumentState[] = [];
-  const contentFingerprint = (d: DocumentState) =>
-    JSON.stringify({
-      sheets: d.sheets,
-      locale: d.locale,
-      csvDelimiter: d.csvDelimiter,
-      customFunctions: d.customFunctions,
-      namedRanges: d.namedRanges,
-      macros: d.macros,
-    });
   let historySnapshot = snapshot();
   let historyFingerprint = contentFingerprint(historySnapshot);
   let historyTimer: ReturnType<typeof setTimeout> | undefined;
@@ -3142,6 +3151,9 @@ function createStore() {
     addTableFromCells,
     replaceTableCells,
     snapshot,
+    flushSave,
+    hasPendingSave,
+    cancelSave,
     engine: () => wb,
   };
 }
diff --git a/src/store/library.ts b/src/store/library.ts
new file mode 100644
index 0000000..fe2204a
--- /dev/null
+++ b/src/store/library.ts
@@ -0,0 +1,341 @@
+/**
+ * Glue between the document store (one open document) and the document
+ * library in IndexedDB (all documents in this browser):
+ *
+ * - which document is open: `?doc=<id>` in the URL, so every browser tab can
+ *   have its own document and a reload reopens the same one;
+ * - persistence: the store's debounced save lands here and is written into
+ *   the library under the open document's id;
+ * - other tabs: a BroadcastChannel tells them when a document's content, the
+ *   list or a title changed, so an open document list stays current and a
+ *   document open in two tabs follows the other tab's saves. Two tabs editing
+ *   the *same* document at the same moment still overwrite each other (last
+ *   save wins), so a hint is shown when that situation arises.
+ */
+
+import { computed, reactive } from 'vue';
+import { useDocument, setPersistHandler, contentFingerprint } from './document';
+import type { DocumentState } from './types';
+import { DocumentLibrary, newDocId, type DocMeta } from '../io/library';
+import { validateDocument } from '../io/json';
+import { createBlankDocument, createSeedDocument } from '../data/seed';
+import { useToasts } from '../composables/useToasts';
+
+/** The single-document localStorage keys used before the library existed --
+ *  read once and moved into the library as its first document. */
+const LEGACY_KEYS = ['numolus:doc:v2', 'numbers-study:doc:v2'];
+const CHANNEL = 'numolus:library';
+const DEFAULT_TITLE = 'Unbenannt';
+const APP_TITLE = 'numolus';
+
+type Msg =
+  | { type: 'list' }
+  | { type: 'saved'; id: string }
+  | { type: 'deleted'; id: string }
+  | { type: 'hello'; id: string }
+  | { type: 'here'; id: string };
+
+function createLibrary() {
+  const store = useDocument();
+  const toasts = useToasts();
+
+  const state = reactive({
+    ready: false,
+    /** false = IndexedDB unavailable (private mode in some browsers, ...) */
+    available: true,
+    docs: [] as DocMeta[],
+    currentId: null as string | null,
+  });
+  const current = computed(() => state.docs.find((d) => d.id === state.currentId) ?? null);
+  const currentTitle = computed(() => current.value?.title ?? DEFAULT_TITLE);
+
+  let lib: DocumentLibrary | null = null;
+  let channel: BroadcastChannel | null = null;
+  /** content fingerprint of what the library holds for the open document */
+  let savedContent = '';
+  /** `updatedAt` of the open document as this tab last wrote or read it --
+   *  a differing value in the library means another tab saved since */
+  let knownUpdatedAt = 0;
+  /** writes run one after another, in order */
+  let writeQueue: Promise<void> = Promise.resolve();
+  /** documents we've already warned about being open in another tab */
+  const warnedShared = new Set<string>();
+
+  const post = (m: Msg) => channel?.postMessage(m);
+  const enqueue = (job: () => Promise<void>) => {
+    writeQueue = writeQueue.then(job).catch((err) => {
+      console.error(err);
+      toasts.error(`Speichern fehlgeschlagen: ${(err as Error).message}`);
+    });
+    return writeQueue;
+  };
+
+  async function refreshList() {
+    if (lib) state.docs = await lib.list();
+  }
+
+  function uniqueTitle(base: string): string {
+    const taken = new Set(state.docs.map((d) => d.title.toLowerCase()));
+    if (!taken.has(base.toLowerCase())) return base;
+    for (let n = 2; ; n++) {
+      const t = `${base} ${n}`;
+      if (!taken.has(t.toLowerCase())) return t;
+    }
+  }
+
+  function setUrl(id: string, push: boolean) {
+    const url = new URL(location.href);
+    if (url.searchParams.get('doc') === id) return;
+    url.searchParams.set('doc', id);
+    if (push) history.pushState(null, '', url);
+    else history.replaceState(null, '', url);
+  }
+
+  function updateWindowTitle() {
+    document.title = `${currentTitle.value} – ${APP_TITLE}`;
+  }
+
+  // ---- persistence ---------------------------------------------------
+  function persist(doc: DocumentState) {
+    const id = state.currentId;
+    if (!lib || !id) return;
+    const json = JSON.stringify(doc);
+    const fp = contentFingerprint(doc);
+    const changed = fp !== savedContent;
+    savedContent = fp;
+    void enqueue(async () => {
+      const meta = (await lib!.getMeta(id)) ?? {
+        id,
+        title: currentTitle.value,
+        createdAt: Date.now(),
+        updatedAt: Date.now(),
+      };
+      if (!changed) {
+        // only the cursor/active sheet moved: saved so reopening restores
+        // it, but never over newer content another tab has written meanwhile
+        if (meta.updatedAt !== knownUpdatedAt) return;
+        await lib!.put(meta, json);
+        return;
+      }
+      const updatedAt = Math.max(Date.now(), meta.updatedAt + 1);
+      await lib!.put({ ...meta, updatedAt }, json);
+      if (id === state.currentId) knownUpdatedAt = updatedAt;
+      await refreshList();
+      post({ type: 'saved', id });
+    });
+  }
+
+  /** Show `json` in the store as the open document `id`. */
+  function show(id: string, json: string, updatedAt: number, keepView = false) {
+    const next = validateDocument(JSON.parse(json));
+    if (keepView) {
+      // another tab's save: take its content, keep this tab's cursor/sheet
+      if (next.sheets.some((s) => s.id === store.doc.activeSheetId)) {
+        next.activeSheetId = store.doc.activeSheetId;
+        next.activeObjectId = store.doc.activeObjectId;
+        next.selection = store.doc.selection;
+      }
+    }
+    state.currentId = id;
+    store.replaceDocument(next);
+    // it came from the library -- writing it straight back would only risk
+    // overwriting a newer save from another tab
+    store.cancelSave();
+    savedContent = contentFingerprint(store.doc);
+    knownUpdatedAt = updatedAt;
+    updateWindowTitle();
+  }
+
+  // ---- opening documents ---------------------------------------------
+  async function open(id: string, opts: { push?: boolean } = {}): Promise<boolean> {
+    if (!lib) return false;
+    if (id === state.currentId) return true;
+    store.flushSave();
+    await writeQueue;
+    const [meta, json] = await Promise.all([lib.getMeta(id), lib.getContent(id)]);
+    if (!meta || json === undefined) return false;
+    try {
+      show(id, json, meta.updatedAt);
+    } catch (err) {
+      toasts.error(`Dokument konnte nicht geladen werden: ${(err as Error).message}`);
+      return false;
+    }
+    setUrl(id, opts.push ?? true);
+    post({ type: 'hello', id });
+    return true;
+  }
+
+  /** Add a document to the library and open it. */
+  async function create(doc: DocumentState, title: string): Promise<string | null> {
+    if (!lib) {
+      // no library: at least show it
+      store.replaceDocument(doc);
+      return null;
+    }
+    const id = newDocId();
+    const now = Date.now();
+    await enqueue(() =>
+      lib!.put({ id, title: uniqueTitle(title.trim() || DEFAULT_TITLE), createdAt: now, updatedAt: now }, JSON.stringify(doc)),
+    );
+    await refreshList();
+    post({ type: 'list' });
+    await open(id);
+    return id;
+  }
+
+  const createBlank = () => create(createBlankDocument(), DEFAULT_TITLE);
+  const createSample = () => create(createSeedDocument(), 'Muster · Umsatzanalyse');
+
+  async function rename(id: string, title: string) {
+    const t = title.trim();
+    if (!lib || !t) return;
+    await enqueue(() => lib!.patchMeta(id, { title: t }));
+    await refreshList();
+    if (id === state.currentId) updateWindowTitle();
+    post({ type: 'list' });
+  }
+
+  async function duplicate(id: string) {
+    if (!lib) return;
+    if (id === state.currentId) store.flushSave();
+    await writeQueue;
+    const [meta, json] = await Promise.all([lib.getMeta(id), lib.getContent(id)]);
+    if (!meta || json === undefined) return;
+    const now = Date.now();
+    await enqueue(() =>
+      lib!.put({ id: newDocId(), title: uniqueTitle(`${meta.title} (Kopie)`), createdAt: now, updatedAt: now }, json),
+    );
+    await refreshList();
+    post({ type: 'list' });
+  }
+
+  async function remove(id: string) {
+    if (!lib) return;
+    await enqueue(() => lib!.remove(id));
+    await refreshList();
+    post({ type: 'deleted', id });
+    if (id === state.currentId) await openFallback();
+  }
+
+  /** Most recently changed document, or a new blank one. */
+  async function openFallback() {
+    state.currentId = null;
+    const next = state.docs[0];
+    if (!next || !(await open(next.id, { push: false }))) await createBlank();
+  }
+
+  // ---- other tabs ------------------------------------------------------
+  async function onMessage(m: Msg) {
+    if (m.type === 'list') {
+      await refreshList();
+      updateWindowTitle();
+    } else if (m.type === 'saved') {
+      await refreshList();
+      // our own unsaved edit wins (it's written right after); otherwise
+      // follow -- a pending save that's only a cursor move doesn't count
+      const localEdit = store.hasPendingSave() && contentFingerprint(store.doc) !== savedContent;
+      if (m.id === state.currentId && !localEdit && lib) {
+        const [meta, json] = await Promise.all([lib.getMeta(m.id), lib.getContent(m.id)]);
+        if (meta && json !== undefined && m.id === state.currentId) show(m.id, json, meta.updatedAt, true);
+      }
+    } else if (m.type === 'deleted') {
+      await refreshList();
+      if (m.id === state.currentId) {
+        toasts.info('Dieses Dokument wurde in einem anderen Tab gelöscht.');
+        await openFallback();
+      }
+    } else if (m.id === state.currentId) {
+      // hello / here: the same document is open in another tab
+      if (m.type === 'hello') post({ type: 'here', id: m.id });
+      if (!warnedShared.has(m.id)) {
+        warnedShared.add(m.id);
+        toasts.info(
+          'Dieses Dokument ist auch in einem anderen Tab geöffnet. Gleichzeitige Änderungen können sich überschreiben.',
+        );
+      }
+    }
+  }
+
+  // ---- start -----------------------------------------------------------
+  async function migrateLegacy() {
+    for (const key of LEGACY_KEYS) {
+      let raw: string | null = null;
+      try {
+        raw = localStorage.getItem(key);
+      } catch {
+        return;
+      }
+      if (!raw) continue;
+      try {
+        const doc = validateDocument(JSON.parse(raw));
+        const now = Date.now();
+        await lib!.put(
+          { id: newDocId(), title: 'Mein Dokument', createdAt: now, updatedAt: now },
+          JSON.stringify(doc),
+        );
+      } catch {
+        continue; // corrupt -- leave it where it is
+      }
+      for (const k of LEGACY_KEYS) localStorage.removeItem(k);
+      return;
+    }
+  }
+
+  async function init() {
+    try {
+      lib = await DocumentLibrary.open();
+    } catch (err) {
+      console.error(err);
+      state.available = false;
+      state.ready = true;
+      toasts.error('Dokumente können in diesem Browser nicht gespeichert werden (IndexedDB nicht verfügbar).');
+      return;
+    }
+    await migrateLegacy();
+    await refreshList();
+
+    if (typeof BroadcastChannel !== 'undefined') {
+      channel = new BroadcastChannel(CHANNEL);
+      channel.onmessage = (e: MessageEvent<Msg>) => void onMessage(e.data);
+    }
+    setPersistHandler(persist);
+
+    const wanted = new URL(location.href).searchParams.get('doc');
+    if (wanted && !(await open(wanted, { push: false }))) {
+      toasts.error('Das angeforderte Dokument gibt es in diesem Browser nicht.');
+    }
+    if (!state.currentId) await openFallback();
+
+    window.addEventListener('popstate', () => {
+      const id = new URL(location.href).searchParams.get('doc');
+      if (id && id !== state.currentId) void open(id, { push: false });
+    });
+    // don't lose the last 250 ms of typing when the tab goes away
+    window.addEventListener('pagehide', () => store.flushSave());
+    document.addEventListener('visibilitychange', () => {
+      if (document.visibilityState === 'hidden') store.flushSave();
+    });
+    state.ready = true;
+  }
+
+  return {
+    state,
+    current,
+    currentTitle,
+    init,
+    open,
+    create,
+    createBlank,
+    createSample,
+    rename,
+    duplicate,
+    remove,
+  };
+}
+
+let instance: ReturnType<typeof createLibrary> | null = null;
+
+export function useLibrary() {
+  if (!instance) instance = createLibrary();
+  return instance;
+}