diff --git a/lib/Controller/NotesController.php b/lib/Controller/NotesController.php
index dc07415c..8dd14de8 100644
--- a/lib/Controller/NotesController.php
+++ b/lib/Controller/NotesController.php
@@ -3,6 +3,7 @@
 namespace OCA\Notes\Controller;
 
 use OCA\Notes\Service\NotesService;
+use OCA\Notes\Service\MetaService;
 use OCA\Notes\Service\SettingsService;
 
 use OCP\AppFramework\Controller;
@@ -16,6 +17,8 @@ class NotesController extends Controller {
 
 	/** @var NotesService */
 	private $notesService;
+	/** @var MetaService */
+	private $metaService;
 	/** @var SettingsService */
 	private $settingsService;
 	/** @var Helper */
@@ -31,6 +34,7 @@ class NotesController extends Controller {
 		string $AppName,
 		IRequest $request,
 		NotesService $notesService,
+		MetaService $metaService,
 		SettingsService $settingsService,
 		Helper $helper,
 		IConfig $settings,
@@ -39,6 +43,7 @@ class NotesController extends Controller {
 	) {
 		parent::__construct($AppName, $request);
 		$this->notesService = $notesService;
+		$this->metaService = $metaService;
 		$this->settingsService = $settingsService;
 		$this->helper = $helper;
 		$this->settings = $settings;
@@ -50,8 +55,9 @@ class NotesController extends Controller {
 	/**
 	 * @NoAdminRequired
 	 */
-	public function index() : JSONResponse {
-		return $this->helper->handleErrorResponse(function () {
+	public function index(int $pruneBefore = 0) : JSONResponse {
+		return $this->helper->handleErrorResponse(function () use ($pruneBefore) {
+			$now = new \DateTime(); // this must be before loading notes if there are concurrent changes possible
 			$settings = $this->settingsService->getAll($this->userId);
 
 			$errorMessage = null;
@@ -65,9 +71,15 @@ class NotesController extends Controller {
 			$categories = null;
 			try {
 				$data = $this->notesService->getAll($this->userId);
+				$metas = $this->metaService->updateAll($this->userId, $data['notes']);
 				$categories = $data['categories'];
-				$notesData = array_map(function ($note) {
-					return $note->getData([ 'content' ]);
+				$notesData = array_map(function ($note) use ($metas, $pruneBefore) {
+					$lastUpdate = $metas[$note->getId()]->getLastUpdate();
+					if ($pruneBefore && $lastUpdate<$pruneBefore) {
+						return [ 'id' => $note->getId() ];
+					} else {
+						return $note->getData([ 'content' ]);
+					}
 				}, $data['notes']);
 				if ($lastViewedNote) {
 					// check if note exists
@@ -83,13 +95,18 @@ class NotesController extends Controller {
 				$errorMessage = $this->l10n->t('The notes folder is not accessible: %s', $e->getMessage());
 			}
 
-			return [
+			$result = [
 				'notes' => $notesData,
 				'categories' => $categories,
 				'settings' => $settings,
 				'lastViewedNote' => $lastViewedNote,
 				'errorMessage' => $errorMessage,
 			];
+			$etag = md5(json_encode($result));
+			return (new JSONResponse($result))
+				->setLastModified($now)
+				->setETag($etag)
+			;
 		});
 	}
 
diff --git a/lib/Service/MetaService.php b/lib/Service/MetaService.php
index f731f317..d7aab439 100644
--- a/lib/Service/MetaService.php
+++ b/lib/Service/MetaService.php
@@ -118,7 +118,13 @@ class MetaService {
 		$meta->setFileId($note->getId());
 		$meta->setLastUpdate(time());
 		$this->updateIfNeeded($meta, $note, true);
-		$this->metaMapper->insert($meta);
+		try {
+			$this->metaMapper->insert($meta);
+			/* @phan-suppress-next-line PhanUndeclaredClassCatch */
+		} catch (\Doctrine\DBAL\Exception\UniqueConstraintViolationException $e) {
+			// It's likely that a concurrent request created this entry, too.
+			// We can ignore this, since the result should be the same.
+		}
 		return $meta;
 	}
 
diff --git a/src/App.vue b/src/App.vue
index 9bfda586..27751eed 100644
--- a/src/App.vue
+++ b/src/App.vue
@@ -67,7 +67,7 @@ export default {
 				search: '',
 			},
 			loading: {
-				notes: false,
+				notes: true,
 				create: false,
 			},
 			error: false,
@@ -79,7 +79,7 @@ export default {
 
 	computed: {
 		notes() {
-			return store.state.notes
+			return store.state.notes.notes
 		},
 
 		filteredNotes() {
@@ -129,9 +129,12 @@ export default {
 
 	methods: {
 		loadNotes() {
-			this.loading.notes = true
 			fetchNotes()
 				.then(data => {
+					if (data === null) {
+						// nothing changed
+						return
+					}
 					if (data.notes !== null) {
 						this.error = false
 						this.routeDefault(data.lastViewedNote)
@@ -140,10 +143,14 @@ export default {
 					}
 				})
 				.catch(() => {
-					this.error = true
+					// only show error state if not loading in background
+					if (this.loading.notes) {
+						this.error = true
+					}
 				})
 				.then(() => {
 					this.loading.notes = false
+					setTimeout(this.loadNotes, 25000)
 				})
 		},
 
@@ -151,7 +158,8 @@ export default {
 			if (this.$route.path !== '/') {
 				this.$router.push('/')
 			}
-			store.commit('removeAll')
+			store.commit('removeAllNotes')
+			this.loading.notes = true
 			this.loadNotes()
 		},
 
diff --git a/src/NotesService.js b/src/NotesService.js
index 473559c6..c633b9eb 100644
--- a/src/NotesService.js
+++ b/src/NotesService.js
@@ -36,23 +36,39 @@ export const setSettings = settings => {
 }
 
 export const fetchNotes = () => {
+	const lastETag = store.state.sync.etag
+	const lastModified = store.state.sync.lastModified
+	const headers = {}
+	if (lastETag) {
+		headers['If-None-Match'] = lastETag
+	}
 	return axios
-		.get(url('/notes'))
+		.get(
+			url('/notes' + (lastModified ? '?pruneBefore=' + lastModified : '')),
+			{ headers }
+		)
 		.then(response => {
 			store.commit('setSettings', response.data.settings)
 			store.commit('setCategories', response.data.categories)
 			if (response.data.notes !== null) {
-				store.dispatch('addAll', response.data.notes)
+				store.dispatch('updateNotes', response.data.notes)
 			}
 			if (response.data.errorMessage) {
 				showError(response.data.errorMessage)
 			}
+			store.commit('setSyncETag', response.headers['etag'])
+			store.commit('setSyncLastModified', response.headers['last-modified'])
 			return response.data
 		})
 		.catch(err => {
-			console.error(err)
-			handleSyncError(t('notes', 'Fetching notes has failed.'))
-			throw err
+			if (err.response && err.response.status === 304) {
+				store.commit('setSyncLastModified', err.response.headers['last-modified'])
+				return null
+			} else {
+				console.error(err)
+				handleSyncError(t('notes', 'Fetching notes has failed.'))
+				throw err
+			}
 		})
 }
 
@@ -63,7 +79,7 @@ export const fetchNote = noteId => {
 			const localNote = store.getters.getNote(parseInt(noteId))
 			// only overwrite if there are no unsaved changes
 			if (!localNote || !localNote.unsaved) {
-				store.commit('add', response.data)
+				store.commit('updateNote', response.data)
 			}
 			return response.data
 		})
@@ -97,7 +113,7 @@ export const createNote = category => {
 	return axios
 		.post(url('/notes'), { category: category })
 		.then(response => {
-			store.commit('add', response.data)
+			store.commit('updateNote', response.data)
 			return response.data
 		})
 		.catch(err => {
@@ -122,7 +138,7 @@ function _updateNote(note) {
 			if (updated.content === note.content) {
 				note.unsaved = false
 			}
-			store.commit('add', note)
+			store.commit('updateNote', note)
 			return note
 		})
 		.catch(err => {
@@ -140,7 +156,7 @@ export const undoDeleteNote = (note) => {
 	return axios
 		.post(url('/notes/undo'), note)
 		.then(response => {
-			store.commit('add', response.data)
+			store.commit('updateNote', response.data)
 			return response.data
 		})
 		.catch(err => {
@@ -159,13 +175,13 @@ export const deleteNote = noteId => {
 	return axios
 		.delete(url('/notes/' + noteId))
 		.then(() => {
-			store.commit('remove', noteId)
+			store.commit('removeNote', noteId)
 		})
 		.catch(err => {
 			console.error(err)
 			handleSyncError(t('notes', 'Deleting note {id} has failed.', { id: noteId }))
 			// remove note always since we don't know when the error happened
-			store.commit('remove', noteId)
+			store.commit('removeNote', noteId)
 			throw err
 		})
 		.then(() => {
@@ -211,8 +227,8 @@ export const saveNote = (noteId, manualSave = false) => {
 }
 
 function _saveNotes() {
-	const unsavedNotes = Object.values(store.state.unsaved)
-	if (store.state.isSaving || unsavedNotes.length === 0) {
+	const unsavedNotes = Object.values(store.state.notes.unsaved)
+	if (store.state.app.isSaving || unsavedNotes.length === 0) {
 		return
 	}
 	store.commit('setSaving', true)
@@ -237,7 +253,7 @@ export const noteExists = (noteId) => {
 export const getCategories = (maxLevel, details) => {
 	const categories = store.getters.getCategories(maxLevel, details)
 	if (maxLevel === 0) {
-		return [...new Set([...categories, ...store.state.categories])]
+		return [...new Set([...categories, ...store.state.notes.categories])]
 	} else {
 		return categories
 	}
diff --git a/src/components/AppSettings.vue b/src/components/AppSettings.vue
index d0318026..e19d8b7a 100644
--- a/src/components/AppSettings.vue
+++ b/src/components/AppSettings.vue
@@ -51,7 +51,7 @@ export default {
 
 	computed: {
 		settings() {
-			return store.state.settings
+			return store.state.app.settings
 		},
 	},
 
diff --git a/src/components/Note.vue b/src/components/Note.vue
index 0731f0ef..ab4acc85 100644
--- a/src/components/Note.vue
+++ b/src/components/Note.vue
@@ -108,10 +108,10 @@ export default {
 			return this.note ? this.note.title : ''
 		},
 		isManualSave() {
-			return store.state.isManualSave
+			return store.state.app.isManualSave
 		},
 		sidebarOpen() {
-			return store.state.sidebarOpen
+			return store.state.app.sidebarOpen
 		},
 	},
 
@@ -163,7 +163,7 @@ export default {
 		},
 
 		onUpdateTitle(title) {
-			const defaultTitle = store.state.documentTitle
+			const defaultTitle = store.state.app.documentTitle
 			if (title) {
 				document.title = title + ' - ' + defaultTitle
 			} else {
@@ -212,7 +212,7 @@ export default {
 		},
 
 		onToggleSidebar() {
-			store.commit('setSidebarOpen', !store.state.sidebarOpen)
+			store.commit('setSidebarOpen', !store.state.app.sidebarOpen)
 			this.actionsOpen = false
 		},
 
@@ -224,7 +224,7 @@ export default {
 					unsaved: true,
 					autotitle: routeIsNewNote(this.$route),
 				}
-				store.commit('add', note)
+				store.commit('updateNote', note)
 				if (this.autosaveTimer === null) {
 					this.autosaveTimer = setTimeout(() => {
 						this.autosaveTimer = null
diff --git a/src/components/Sidebar.vue b/src/components/Sidebar.vue
index 28f686cc..2f4a7a85 100644
--- a/src/components/Sidebar.vue
+++ b/src/components/Sidebar.vue
@@ -138,7 +138,7 @@ export default {
 			return [ '', ...getCategories(0, false) ]
 		},
 		sidebarOpen() {
-			return store.state.sidebarOpen
+			return store.state.app.sidebarOpen
 		},
 	},
 
diff --git a/src/store.js b/src/store.js
index 4514ea0d..683967f2 100644
--- a/src/store.js
+++ b/src/store.js
@@ -1,166 +1,16 @@
 import Vue from 'vue'
 import Vuex from 'vuex'
 
+import app from './store/app'
+import notes from './store/notes'
+import sync from './store/sync'
+
 Vue.use(Vuex)
 
 export default new Vuex.Store({
-	state: {
-		settings: {},
-		categories: [],
-		notes: [],
-		notesIds: {},
-		unsaved: {},
-		isSaving: false,
-		isManualSave: false,
-		documentTitle: null,
-		sidebarOpen: false,
-	},
-
-	getters: {
-		numNotes: (state) => () => {
-			return state.notes.length
-		},
-
-		noteExists: (state) => (id) => {
-			return state.notesIds[id] !== undefined
-		},
-
-		getNote: (state) => (id) => {
-			if (state.notesIds[id] === undefined) {
-				return null
-			}
-			return state.notesIds[id]
-		},
-
-		getCategories: (state) => (maxLevel, details) => {
-			function nthIndexOf(str, pattern, n) {
-				let i = -1
-				while (n-- && i++ < str.length) {
-					i = str.indexOf(pattern, i)
-					if (i < 0) {
-						break
-					}
-				}
-				return i
-			}
-
-			// get categories from notes
-			const categories = {}
-			for (const note of state.notes) {
-				let cat = note.category
-				if (maxLevel > 0) {
-					const index = nthIndexOf(cat, '/', maxLevel)
-					if (index > 0) {
-						cat = cat.substring(0, index)
-					}
-				}
-				if (categories[cat] === undefined) {
-					categories[cat] = 1
-				} else {
-					categories[cat] += 1
-				}
-			}
-			// get structured result from categories
-			const result = []
-			for (const category in categories) {
-				if (details) {
-					result.push({
-						name: category,
-						count: categories[category],
-					})
-				} else if (category) {
-					result.push(category)
-				}
-			}
-			if (details) {
-				result.sort((a, b) => a.name.localeCompare(b.name))
-			} else {
-				result.sort()
-			}
-			return result
-		},
-	},
-
-	mutations: {
-		add(state, updated) {
-			const note = state.notesIds[updated.id]
-			if (note) {
-				// don't update meta-data over full data
-				if (updated.content !== undefined || note.content === undefined) {
-					note.title = updated.title
-					note.modified = updated.modified
-					note.content = updated.content
-					note.favorite = updated.favorite
-					note.category = updated.category
-					Vue.set(note, 'autotitle', updated.autotitle)
-					Vue.set(note, 'unsaved', updated.unsaved)
-					Vue.set(note, 'error', updated.error)
-					Vue.set(note, 'errorMessage', updated.errorMessage)
-				}
-			} else {
-				state.notes.push(updated)
-				Vue.set(state.notesIds, updated.id, updated)
-			}
-		},
-
-		setNoteAttribute(state, params) {
-			const note = state.notesIds[params.noteId]
-			if (note) {
-				Vue.set(note, params.attribute, params.value)
-			}
-		},
-
-		remove(state, id) {
-			const index = state.notes.findIndex(note => note.id === id)
-			if (index !== -1) {
-				state.notes.splice(index, 1)
-				delete state.notesIds[id]
-			}
-		},
-
-		removeAll(state) {
-			state.notes = []
-			state.notesIds = {}
-		},
-
-		addUnsaved(state, id) {
-			Vue.set(state.unsaved, id, state.notesIds[id])
-		},
-
-		clearUnsaved(state) {
-			state.unsaved = {}
-		},
-
-		setSettings(state, settings) {
-			state.settings = settings
-		},
-
-		setCategories(state, categories) {
-			state.categories = categories
-		},
-
-		setSaving(state, isSaving) {
-			state.isSaving = isSaving
-		},
-
-		setManualSave(state, isManualSave) {
-			state.isManualSave = isManualSave
-		},
-
-		setDocumentTitle(state, title) {
-			state.documentTitle = title
-		},
-
-		setSidebarOpen(state, open) {
-			state.sidebarOpen = open
-		},
-	},
-
-	actions: {
-		addAll(context, notes) {
-			for (const note of notes) {
-				context.commit('add', note)
-			}
-		},
+	modules: {
+		app,
+		notes,
+		sync,
 	},
 })
diff --git a/src/store/app.js b/src/store/app.js
new file mode 100644
index 00000000..3f291bee
--- /dev/null
+++ b/src/store/app.js
@@ -0,0 +1,37 @@
+const state = {
+	settings: {},
+	isSaving: false,
+	isManualSave: false,
+	documentTitle: null,
+	sidebarOpen: false,
+}
+
+const getters = {
+}
+
+const mutations = {
+	setSettings(state, settings) {
+		state.settings = settings
+	},
+
+	setSaving(state, isSaving) {
+		state.isSaving = isSaving
+	},
+
+	setManualSave(state, isManualSave) {
+		state.isManualSave = isManualSave
+	},
+
+	setDocumentTitle(state, title) {
+		state.documentTitle = title
+	},
+
+	setSidebarOpen(state, open) {
+		state.sidebarOpen = open
+	},
+}
+
+const actions = {
+}
+
+export default { state, getters, mutations, actions }
diff --git a/src/store/notes.js b/src/store/notes.js
new file mode 100644
index 00000000..e33dfa7d
--- /dev/null
+++ b/src/store/notes.js
@@ -0,0 +1,151 @@
+import Vue from 'vue'
+
+const state = {
+	categories: [],
+	notes: [],
+	notesIds: {},
+	unsaved: {},
+}
+
+const getters = {
+	numNotes: (state) => () => {
+		return state.notes.length
+	},
+
+	noteExists: (state) => (id) => {
+		return state.notesIds[id] !== undefined
+	},
+
+	getNote: (state) => (id) => {
+		if (state.notesIds[id] === undefined) {
+			return null
+		}
+		return state.notesIds[id]
+	},
+
+	getCategories: (state) => (maxLevel, details) => {
+		function nthIndexOf(str, pattern, n) {
+			let i = -1
+			while (n-- && i++ < str.length) {
+				i = str.indexOf(pattern, i)
+				if (i < 0) {
+					break
+				}
+			}
+			return i
+		}
+
+		// get categories from notes
+		const categories = {}
+		for (const note of state.notes) {
+			let cat = note.category
+			if (maxLevel > 0) {
+				const index = nthIndexOf(cat, '/', maxLevel)
+				if (index > 0) {
+					cat = cat.substring(0, index)
+				}
+			}
+			if (categories[cat] === undefined) {
+				categories[cat] = 1
+			} else {
+				categories[cat] += 1
+			}
+		}
+		// get structured result from categories
+		const result = []
+		for (const category in categories) {
+			if (details) {
+				result.push({
+					name: category,
+					count: categories[category],
+				})
+			} else if (category) {
+				result.push(category)
+			}
+		}
+		if (details) {
+			result.sort((a, b) => a.name.localeCompare(b.name))
+		} else {
+			result.sort()
+		}
+		return result
+	},
+}
+
+const mutations = {
+	updateNote(state, updated) {
+		const note = state.notesIds[updated.id]
+		if (note) {
+			// don't update meta-data over full data
+			if (updated.content !== undefined || note.content === undefined) {
+				note.title = updated.title
+				note.modified = updated.modified
+				note.content = updated.content
+				note.favorite = updated.favorite
+				note.category = updated.category
+				Vue.set(note, 'autotitle', updated.autotitle)
+				Vue.set(note, 'unsaved', updated.unsaved)
+				Vue.set(note, 'error', updated.error)
+				Vue.set(note, 'errorMessage', updated.errorMessage)
+			}
+		} else {
+			state.notes.push(updated)
+			Vue.set(state.notesIds, updated.id, updated)
+		}
+	},
+
+	setNoteAttribute(state, params) {
+		const note = state.notesIds[params.noteId]
+		if (note) {
+			Vue.set(note, params.attribute, params.value)
+		}
+	},
+
+	removeNote(state, id) {
+		const index = state.notes.findIndex(note => note.id === id)
+		if (index !== -1) {
+			state.notes.splice(index, 1)
+			delete state.notesIds[id]
+		}
+	},
+
+	removeAllNotes(state) {
+		state.notes = []
+		state.notesIds = {}
+	},
+
+	addUnsaved(state, id) {
+		Vue.set(state.unsaved, id, state.notesIds[id])
+	},
+
+	clearUnsaved(state) {
+		state.unsaved = {}
+	},
+
+	setCategories(state, categories) {
+		state.categories = categories
+	},
+}
+
+const actions = {
+	updateNotes(context, notes) {
+		const noteIds = {}
+		// add/update new notes
+		for (const note of notes) {
+			noteIds[note.id] = true
+			// TODO check for parallel (local) changes!
+			// only update, if note has changes (see API "purgeBefore")
+			if (note.title !== undefined) {
+				context.commit('updateNote', note)
+			}
+		}
+		// remove deleted notes
+		context.state.notes.forEach(note => {
+			if (noteIds[note.id] === undefined) {
+				context.commit('removeNote', note.id)
+			}
+		})
+	},
+}
+
+export default { state, getters, mutations, actions }
diff --git a/src/store/sync.js b/src/store/sync.js
new file mode 100644
index 00000000..dbc38e1d
--- /dev/null
+++ b/src/store/sync.js
@@ -0,0 +1,33 @@
+const state = {
+	etag: null,
+	lastModified: 0,
+	active: false,
+	// TODO add list of notes with changes during sync
+}
+
+const getters = {
+}
+
+const mutations = {
+	setSyncETag(state, etag) {
+		if (etag) {
+			state.etag = etag
+		}
+	},
+
+	setSyncLastModified(state, strLastModified) {
+		const lastModified = Date.parse(strLastModified)
+		if (lastModified) {
+			state.lastModified = lastModified / 1000
+		}
+	},
+
+	setSyncActive(state, active) {
+		state.active = active
+	},
+}
+
+const actions = {
+}
+
+export default { state, getters, mutations, actions }