diff --git a/build.gradle b/build.gradle
index c5e9b34..d6a397d 100644
--- a/build.gradle
+++ b/build.gradle
@@ -83,7 +83,6 @@ kotlin {
                 implementation "io.ktor:ktor-server-netty:$ktor_version"
                 implementation "io.ktor:ktor-auth:$ktor_version"
                 implementation "io.ktor:ktor-server-sessions:$ktor_version"
-                implementation "io.ktor:ktor-websockets:$ktor_version"
                 implementation "io.ktor:ktor-jackson:$ktor_version"
                 implementation 'org.jetbrains:kotlin-css-jvm:1.0.0-pre.70-kotlin-1.3.21'
 
diff --git a/src/commonMain/kotlin/de/kif/common/ConstraintChecking.kt b/src/commonMain/kotlin/de/kif/common/ConstraintChecking.kt
index 78e2ee8..8f3071c 100644
--- a/src/commonMain/kotlin/de/kif/common/ConstraintChecking.kt
+++ b/src/commonMain/kotlin/de/kif/common/ConstraintChecking.kt
@@ -48,8 +48,8 @@ fun checkConstraints(
                 if (
                     schedule != s &&
                     leader in s.workGroup.leader &&
-                    start <= s.getAbsoluteEndTime() &&
-                    s.getAbsoluteStartTime() <= end
+                    start < s.getAbsoluteEndTime() &&
+                    s.getAbsoluteStartTime() < end
                 ) {
                     errors += ConstraintError("Work group with leader $leader cannot be at same time with ${s.workGroup.name}!")
                 }
diff --git a/src/commonMain/kotlin/de/kif/common/Message.kt b/src/commonMain/kotlin/de/kif/common/Message.kt
index e239280..e48a65b 100644
--- a/src/commonMain/kotlin/de/kif/common/Message.kt
+++ b/src/commonMain/kotlin/de/kif/common/Message.kt
@@ -1,35 +1,38 @@
 package de.kif.common
 
+import kotlinx.serialization.DeserializationStrategy
 import kotlinx.serialization.Serializable
+import kotlinx.serialization.SerializationStrategy
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.modules.SerializersModule
 
+@Serializable
+data class MessageBox(
+    val timestamp: Long,
+    val valid: Boolean,
+    val messages: List<Message>
+)
+
 @Serializable
 data class Message(
     val type: MessageType,
     val repository: RepositoryType,
     val id: Long
-) {
-
-    fun stringify(): String {
-        return json.stringify(serializer(), this)
-    }
-
-    companion object {
-        private val jsonContext = SerializersModule {}
-
-        val json = Json(context = jsonContext)
-
-        fun parse(data: String): Message {
-            return json.parse(serializer(), data)
-        }
-    }
-}
+)
 
 enum class MessageType {
     CREATE, UPDATE, DELETE
 }
 
 enum class RepositoryType {
-    ROOM, SCHEDULE, TRACK, USER, WORK_GROUP, POST
+    ROOM, SCHEDULE, TRACK, USER, WORK_GROUP, POST, ANNOUNCEMENT
+}
+
+object Serialization {
+    private val jsonContext = SerializersModule {}
+
+    val json = Json(context = jsonContext)
+
+    fun <T> stringify(serializer: SerializationStrategy<T>, obj: T) = json.stringify(serializer, obj)
+    fun <T> parse(serializer: DeserializationStrategy<T>, str: String) = json.parse(serializer, str)
 }
diff --git a/src/commonMain/kotlin/de/kif/common/Search.kt b/src/commonMain/kotlin/de/kif/common/Search.kt
index fadef97..184518d 100644
--- a/src/commonMain/kotlin/de/kif/common/Search.kt
+++ b/src/commonMain/kotlin/de/kif/common/Search.kt
@@ -10,12 +10,12 @@ data class SearchElement(
 ) {
 
     fun stringify(): String {
-        return Message.json.stringify(serializer(), this)
+        return Serialization.stringify(serializer(), this)
     }
 
     companion object {
         fun parse(data: String): SearchElement {
-            return Message.json.parse(serializer(), data)
+            return Serialization.parse(serializer(), data)
         }
     }
 }
diff --git a/src/jsMain/kotlin/de/kif/frontend/WebSocketClient.kt b/src/jsMain/kotlin/de/kif/frontend/WebSocketClient.kt
index 62464af..1a72f25 100644
--- a/src/jsMain/kotlin/de/kif/frontend/WebSocketClient.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/WebSocketClient.kt
@@ -1,68 +1,92 @@
 package de.kif.frontend
 
-import de.kif.common.Message
+import de.kif.common.MessageBox
 import de.kif.common.MessageType
 import de.kif.common.RepositoryType
 import de.kif.frontend.repository.*
-import de.westermann.kwebview.async
-import org.w3c.dom.MessageEvent
-import org.w3c.dom.WebSocket
-import org.w3c.dom.events.Event
+import de.westermann.kwebview.clearInterval
+import de.westermann.kwebview.createHtmlView
+import de.westermann.kwebview.interval
+import kotlinx.serialization.DynamicObjectParser
+import org.w3c.dom.get
+import org.w3c.xhr.XMLHttpRequest
+import kotlin.browser.document
 import kotlin.browser.window
 
-class WebSocketClient() {
+class WebSocketClient {
     private val prefix = js("prefix")
+    private val url = "$prefix/api/updates"
+    private val body = document.body ?: createHtmlView()
+    private val parser = DynamicObjectParser()
 
-    private val useSsl = "https" in window.location.protocol
-    private val wsProtocol = if (useSsl) "wss" else "ws"
-    private val url = "$wsProtocol://${window.location.host}$prefix/websocket"
+    private var timestamp = body.dataset["timestamp"]?.toLongOrNull() ?: 0L
+    private var intervalId: Int? = null
 
-    private lateinit var ws: WebSocket
-    private var reconnect = false
+    private fun reload() {
+        val id = intervalId ?: return
+        clearInterval(id)
+        intervalId = null
 
-    @Suppress("UNUSED_PARAMETER")
-    private fun onOpen(event: Event) {
-        console.log("Connected!")
-        if (reconnect) {
-            window.location.reload()
-        }
+        window.location.reload()
     }
 
-    private fun onMessage(messageEvent: MessageEvent) {
-        val message = Message.parse(messageEvent.data?.toString() ?: "")
+    private fun onMessage(messageBox: MessageBox) {
+        body.classList.remove("offline")
 
-        for (handler in messageHandlers) {
-            if (handler.repository == message.repository) {
-                when (message.type) {
-                    MessageType.CREATE -> handler.onCreate(message.id)
-                    MessageType.UPDATE -> handler.onUpdate(message.id)
-                    MessageType.DELETE -> handler.onDelete(message.id)
+        if (messageBox.valid) {
+            timestamp = messageBox.timestamp
+
+            for (message in messageBox.messages) {
+                for (handler in messageHandlers) {
+                    if (handler.repository == message.repository) {
+                        when (message.type) {
+                            MessageType.CREATE -> handler.onCreate(message.id)
+                            MessageType.UPDATE -> handler.onUpdate(message.id)
+                            MessageType.DELETE -> handler.onDelete(message.id)
+                        }
+                    }
                 }
             }
+        } else {
+            reload()
         }
     }
 
-    @Suppress("UNUSED_PARAMETER")
-    private fun onClose(event: Event) {
-        console.log("Disconnected!")
-        reconnect = true
-        async(1000) {
-            connect()
+    private fun onError(code: Int) {
+        if (!body.classList.contains("offline")) {
+            console.log("Offline reason: $code")
         }
+        body.classList.add("offline")
     }
 
-    @Suppress("UNUSED_PARAMETER")
-    private fun onError(event: Event) {
-        console.log("An error occurred!")
-    }
+    private fun request() {
+        val xmlHttpRequest = XMLHttpRequest()
 
-    private fun connect() {
-        ws = WebSocket(url)
+        xmlHttpRequest.onreadystatechange = {
+            try {
+                if (xmlHttpRequest.readyState == 4.toShort()) {
+                    if (xmlHttpRequest.status == 200.toShort() || xmlHttpRequest.status == 304.toShort()) {
+                        val json = JSON.parse<JsonResponse>(xmlHttpRequest.responseText)
 
-        ws.onopen = this::onOpen
-        ws.onmessage = this::onMessage
-        ws.onclose = this::onClose
-        ws.onerror = this::onError
+                        if (json.OK) {
+                            val message = parser.parse(json.data, MessageBox.serializer())
+                            onMessage(message)
+                        } else {
+                            onError(-1)
+                        }
+
+                    } else {
+                        onError(xmlHttpRequest.status.toInt())
+                    }
+                }
+            } catch (e: Exception) {
+                console.error(e)
+                onError(-2)
+            }
+        }
+        xmlHttpRequest.open("GET", "$url?timestamp=$timestamp", true)
+        xmlHttpRequest.overrideMimeType("application/json")
+        xmlHttpRequest.send()
     }
 
     private val messageHandlers: List<MessageHandler> = listOf(
@@ -71,11 +95,14 @@ class WebSocketClient() {
         TrackRepository.handler,
         UserRepository.handler,
         WorkGroupRepository.handler,
-        PostRepository.handler
+        PostRepository.handler,
+        AnnouncementRepository.handler
     )
 
     init {
-        connect()
+        intervalId = interval(500) {
+            request()
+        }
     }
 }
 
diff --git a/src/jsMain/kotlin/de/kif/frontend/main.kt b/src/jsMain/kotlin/de/kif/frontend/main.kt
index ed186cf..7f10c8c 100644
--- a/src/jsMain/kotlin/de/kif/frontend/main.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/main.kt
@@ -2,6 +2,7 @@ package de.kif.frontend
 
 import de.kif.frontend.views.board.initBoard
 import de.kif.frontend.views.calendar.initCalendar
+import de.kif.frontend.views.initAnnouncement
 import de.kif.frontend.views.table.initTableLayout
 import de.kif.frontend.views.initWorkGroupConstraints
 import de.kif.frontend.views.overview.initOverviewMain
@@ -34,4 +35,7 @@ fun main() = init {
     if (document.getElementsByClassName("board").length > 0) {
         initBoard()
     }
+    if (document.getElementsByClassName("announcement").length > 0) {
+        initAnnouncement()
+    }
 }
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/Ajax.kt b/src/jsMain/kotlin/de/kif/frontend/repository/Ajax.kt
index a08991d..1f5446b 100644
--- a/src/jsMain/kotlin/de/kif/frontend/repository/Ajax.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/Ajax.kt
@@ -8,10 +8,15 @@ import kotlin.coroutines.resumeWithException
 import kotlin.coroutines.suspendCoroutine
 import kotlin.js.Promise
 
+interface JsonResponse {
+    val OK: Boolean
+    val data: dynamic
+}
+
 suspend fun repositoryGet(
     url: String
 ): dynamic {
-    val promise = Promise<dynamic> { resolve, reject ->
+    val promise = Promise<JsonResponse> { resolve, reject ->
         val xhttp = XMLHttpRequest()
 
         xhttp.onreadystatechange = {
@@ -47,7 +52,7 @@ suspend fun repositoryPost(
     url: String,
     data: String? = null
 ): dynamic {
-    val promise = Promise<dynamic> { resolve, reject ->
+    val promise = Promise<JsonResponse> { resolve, reject ->
         val xhttp = XMLHttpRequest()
 
         xhttp.onreadystatechange = {
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/AnnouncementRepository.kt b/src/jsMain/kotlin/de/kif/frontend/repository/AnnouncementRepository.kt
new file mode 100644
index 0000000..59a1965
--- /dev/null
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/AnnouncementRepository.kt
@@ -0,0 +1,40 @@
+package de.kif.frontend.repository
+
+import de.kif.common.Message
+import de.kif.common.Repository
+import de.kif.common.RepositoryType
+import de.kif.common.Serialization
+import de.kif.common.model.Room
+import de.kif.frontend.MessageHandler
+import de.westermann.kobserve.event.EventHandler
+import kotlinx.serialization.DynamicObjectParser
+import kotlinx.serialization.list
+import kotlinx.serialization.serializer
+
+object AnnouncementRepository {
+
+    private val prefix = js("prefix")
+
+    val onUpdate = EventHandler<Unit>()
+
+    private val parser = DynamicObjectParser()
+
+    suspend fun getAnnouncement(): String {
+        val json = repositoryGet("$prefix/api/announcement") ?: return ""
+        return parser.parse(json, String.serializer())
+    }
+
+    suspend fun setAnnouncement(value: String){
+        return repositoryPost("$prefix/api/announcement", Serialization.stringify(String.serializer(), value))
+            ?: throw IllegalStateException("Cannot set announcement!")
+    }
+
+    val handler = object : MessageHandler(RepositoryType.ROOM) {
+
+        override fun onCreate(id: Long) {}
+
+        override fun onUpdate(id: Long) = onUpdate.emit(Unit)
+
+        override fun onDelete(id: Long) {}
+    }
+}
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/PostRepository.kt b/src/jsMain/kotlin/de/kif/frontend/repository/PostRepository.kt
index aa56570..13c459e 100644
--- a/src/jsMain/kotlin/de/kif/frontend/repository/PostRepository.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/PostRepository.kt
@@ -3,6 +3,7 @@ package de.kif.frontend.repository
 import de.kif.common.Message
 import de.kif.common.Repository
 import de.kif.common.RepositoryType
+import de.kif.common.Serialization
 import de.kif.common.model.Post
 import de.kif.frontend.MessageHandler
 import de.westermann.kobserve.event.EventHandler
@@ -25,13 +26,13 @@ object PostRepository : Repository<Post> {
     }
 
     override suspend fun create(model: Post): Long {
-        return repositoryPost("$prefix/api/posts", Message.json.stringify(Post.serializer(), model))
+        return repositoryPost("$prefix/api/posts", Serialization.stringify(Post.serializer(), model))
             ?: throw IllegalStateException("Cannot create model!")
     }
 
     override suspend fun update(model: Post) {
         if (model.id == null) throw IllegalStateException("Cannot update model which was not created!")
-        repositoryPost("$prefix/api/post/${model.id}", Message.json.stringify(Post.serializer(), model))
+        repositoryPost("$prefix/api/post/${model.id}", Serialization.stringify(Post.serializer(), model))
     }
 
     override suspend fun delete(id: Long) {
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/RoomRepository.kt b/src/jsMain/kotlin/de/kif/frontend/repository/RoomRepository.kt
index 1dc88ee..9d933f3 100644
--- a/src/jsMain/kotlin/de/kif/frontend/repository/RoomRepository.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/RoomRepository.kt
@@ -3,6 +3,7 @@ package de.kif.frontend.repository
 import de.kif.common.Message
 import de.kif.common.Repository
 import de.kif.common.RepositoryType
+import de.kif.common.Serialization
 import de.kif.common.model.Room
 import de.kif.frontend.MessageHandler
 import de.westermann.kobserve.event.EventHandler
@@ -25,13 +26,13 @@ object RoomRepository : Repository<Room> {
     }
 
     override suspend fun create(model: Room): Long {
-        return repositoryPost("$prefix/api/rooms", Message.json.stringify(Room.serializer(), model))
+        return repositoryPost("$prefix/api/rooms", Serialization.stringify(Room.serializer(), model))
             ?: throw IllegalStateException("Cannot create model!")
     }
 
     override suspend fun update(model: Room) {
         if (model.id == null) throw IllegalStateException("Cannot update model which was not created!")
-        repositoryPost("$prefix/api/room/${model.id}", Message.json.stringify(Room.serializer(), model))
+        repositoryPost("$prefix/api/room/${model.id}", Serialization.stringify(Room.serializer(), model))
     }
 
     override suspend fun delete(id: Long) {
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/ScheduleRepository.kt b/src/jsMain/kotlin/de/kif/frontend/repository/ScheduleRepository.kt
index 60a2b73..3da61bf 100644
--- a/src/jsMain/kotlin/de/kif/frontend/repository/ScheduleRepository.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/ScheduleRepository.kt
@@ -1,9 +1,6 @@
 package de.kif.frontend.repository
 
-import de.kif.common.ConstraintMap
-import de.kif.common.Message
-import de.kif.common.Repository
-import de.kif.common.RepositoryType
+import de.kif.common.*
 import de.kif.common.model.Schedule
 import de.kif.frontend.MessageHandler
 import de.westermann.kobserve.event.EventHandler
@@ -31,13 +28,13 @@ object ScheduleRepository : Repository<Schedule> {
     }
 
     override suspend fun create(model: Schedule): Long {
-        return repositoryPost("$prefix/api/schedules", Message.json.stringify(Schedule.serializer(), model))
+        return repositoryPost("$prefix/api/schedules", Serialization.stringify(Schedule.serializer(), model))
             ?: throw IllegalStateException("Cannot create model!")
     }
 
     override suspend fun update(model: Schedule) {
         if (model.id == null) throw IllegalStateException("Cannot update model which was not created!")
-        repositoryPost("$prefix/api/schedule/${model.id}", Message.json.stringify(Schedule.serializer(), model))
+        repositoryPost("$prefix/api/schedule/${model.id}", Serialization.stringify(Schedule.serializer(), model))
     }
 
     override suspend fun delete(id: Long) {
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/TrackRepository.kt b/src/jsMain/kotlin/de/kif/frontend/repository/TrackRepository.kt
index cf5dcae..754cdef 100644
--- a/src/jsMain/kotlin/de/kif/frontend/repository/TrackRepository.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/TrackRepository.kt
@@ -3,6 +3,7 @@ package de.kif.frontend.repository
 import de.kif.common.Message
 import de.kif.common.Repository
 import de.kif.common.RepositoryType
+import de.kif.common.Serialization
 import de.kif.common.model.Track
 import de.kif.frontend.MessageHandler
 import de.westermann.kobserve.event.EventHandler
@@ -25,13 +26,13 @@ object TrackRepository : Repository<Track> {
     }
 
     override suspend fun create(model: Track): Long {
-        return repositoryPost("$prefix/api/tracks", Message.json.stringify(Track.serializer(), model))
+        return repositoryPost("$prefix/api/tracks", Serialization.stringify(Track.serializer(), model))
             ?: throw IllegalStateException("Cannot create model!")
     }
 
     override suspend fun update(model: Track) {
         if (model.id == null) throw IllegalStateException("Cannot update model which was not created!")
-        repositoryPost("$prefix/api/track/${model.id}", Message.json.stringify(Track.serializer(), model))
+        repositoryPost("$prefix/api/track/${model.id}", Serialization.stringify(Track.serializer(), model))
     }
 
     override suspend fun delete(id: Long) {
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/UserRepository.kt b/src/jsMain/kotlin/de/kif/frontend/repository/UserRepository.kt
index b5a42db..90c0438 100644
--- a/src/jsMain/kotlin/de/kif/frontend/repository/UserRepository.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/UserRepository.kt
@@ -3,6 +3,7 @@ package de.kif.frontend.repository
 import de.kif.common.Message
 import de.kif.common.Repository
 import de.kif.common.RepositoryType
+import de.kif.common.Serialization
 import de.kif.common.model.User
 import de.kif.frontend.MessageHandler
 import de.westermann.kobserve.event.EventHandler
@@ -25,13 +26,13 @@ object UserRepository : Repository<User> {
     }
 
     override suspend fun create(model: User): Long {
-        return repositoryPost("$prefix/api/users", Message.json.stringify(User.serializer(), model))
+        return repositoryPost("$prefix/api/users", Serialization.stringify(User.serializer(), model))
             ?: throw IllegalStateException("Cannot create model!")
     }
 
     override suspend fun update(model: User) {
         if (model.id == null) throw IllegalStateException("Cannot update model which was not created!")
-        repositoryPost("$prefix/api/user/${model.id}", Message.json.stringify(User.serializer(), model))
+        repositoryPost("$prefix/api/user/${model.id}", Serialization.stringify(User.serializer(), model))
     }
 
     override suspend fun delete(id: Long) {
diff --git a/src/jsMain/kotlin/de/kif/frontend/repository/WorkGroupRepository.kt b/src/jsMain/kotlin/de/kif/frontend/repository/WorkGroupRepository.kt
index 18c240c..6714c71 100644
--- a/src/jsMain/kotlin/de/kif/frontend/repository/WorkGroupRepository.kt
+++ b/src/jsMain/kotlin/de/kif/frontend/repository/WorkGroupRepository.kt
@@ -3,6 +3,7 @@ package de.kif.frontend.repository
 import de.kif.common.Message
 import de.kif.common.Repository
 import de.kif.common.RepositoryType
+import de.kif.common.Serialization
 import de.kif.common.model.WorkGroup
 import de.kif.frontend.MessageHandler
 import de.westermann.kobserve.event.EventHandler
@@ -25,13 +26,13 @@ object WorkGroupRepository : Repository<WorkGroup> {
     }
 
     override suspend fun create(model: WorkGroup): Long {
-        return repositoryPost("$prefix/api/workgroups", Message.json.stringify(WorkGroup.serializer(), model))
+        return repositoryPost("$prefix/api/workgroups", Serialization.stringify(WorkGroup.serializer(), model))
             ?: throw IllegalStateException("Cannot create model!")
     }
 
     override suspend fun update(model: WorkGroup) {
         if (model.id == null) throw IllegalStateException("Cannot update model which was not created!")
-        repositoryPost("$prefix/api/workgroup/${model.id}", Message.json.stringify(WorkGroup.serializer(), model))
+        repositoryPost("$prefix/api/workgroup/${model.id}", Serialization.stringify(WorkGroup.serializer(), model))
     }
 
     override suspend fun delete(id: Long) {
diff --git a/src/jsMain/kotlin/de/kif/frontend/views/Announcements.kt b/src/jsMain/kotlin/de/kif/frontend/views/Announcements.kt
new file mode 100644
index 0000000..4c65cc8
--- /dev/null
+++ b/src/jsMain/kotlin/de/kif/frontend/views/Announcements.kt
@@ -0,0 +1,21 @@
+package de.kif.frontend.views
+
+import de.kif.frontend.launch
+import de.kif.frontend.repository.AnnouncementRepository
+import org.w3c.dom.HTMLElement
+import org.w3c.dom.get
+import kotlin.browser.document
+
+fun initAnnouncement() {
+    val announcement = document.getElementsByClassName("announcement")[0] as? HTMLElement ?: return
+    val span = announcement.children[0] as? HTMLElement ?: return
+
+    AnnouncementRepository.onUpdate {
+        launch {
+            val text = AnnouncementRepository.getAnnouncement()
+
+            announcement.classList.toggle("announcement-blank", text.isBlank())
+            span.textContent = text
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/jsMain/resources/style/components/_board.scss b/src/jsMain/resources/style/components/_board.scss
index 4abf210..22ffc32 100644
--- a/src/jsMain/resources/style/components/_board.scss
+++ b/src/jsMain/resources/style/components/_board.scss
@@ -58,7 +58,7 @@
     width: 100%;
     height: 100%;
     border-bottom: solid 1px var(--table-border-color);
-    box-shadow: 0 0 4px black;
+    box-shadow: 0 0 4px var(--shadow-color);
     top: -1rem;
     padding-top: 1.2rem;
   }
@@ -205,3 +205,10 @@
     margin-top: -1px !important;
   }
 }
+
+.board-announcement {
+  position: fixed;
+  bottom: 3rem;
+  z-index: 10;
+  margin-bottom: 0 !important;
+}
diff --git a/src/jsMain/resources/style/style.scss b/src/jsMain/resources/style/style.scss
index a55129c..4f12582 100644
--- a/src/jsMain/resources/style/style.scss
+++ b/src/jsMain/resources/style/style.scss
@@ -160,3 +160,42 @@ a {
     }
   }
 }
+
+.offline-banner {
+  position: fixed;
+  bottom: 3rem;
+  left: 0;
+  right: 0;
+  height: 3rem;
+  line-height: 3rem;
+  text-align: center;
+  font-size: 1.2rem;
+  background-color: var(--primary-color);
+  color: var(--primary-text-color);
+  z-index: 12;
+  box-shadow: 0 1px 4px var(--shadow-color);
+  display: none;
+}
+
+body.offline {
+  .offline-banner {
+    display: block;
+  }
+}
+
+.announcement {
+  height: 3rem;
+  line-height: 3rem;
+  text-align: center;
+  width: 100%;
+  font-size: 1.2rem;
+  background-color: var(--primary-color);
+  color: var(--primary-text-color);
+  box-shadow: 0 1px 4px var(--shadow-color);
+  margin-bottom: 1rem;
+  display: block;
+
+  &.announcement-blank {
+    display: none;
+  }
+}
diff --git a/src/jvmMain/kotlin/de/kif/backend/Application.kt b/src/jvmMain/kotlin/de/kif/backend/Application.kt
index 008d8b5..e7efee4 100644
--- a/src/jvmMain/kotlin/de/kif/backend/Application.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/Application.kt
@@ -15,7 +15,6 @@ import io.ktor.jackson.jackson
 import io.ktor.response.respond
 import io.ktor.routing.route
 import io.ktor.routing.routing
-import io.ktor.websocket.WebSockets
 import org.slf4j.event.Level
 import java.nio.file.Paths
 
@@ -31,7 +30,7 @@ fun Application.main() {
     install(ConditionalHeaders)
     install(Compression)
     install(DataConversion)
-    install(WebSockets)
+    install(AutoHeadResponse)
 
     install(StatusPages) {
         exception<Throwable> {
@@ -91,6 +90,7 @@ fun Application.main() {
             workGroupApi()
             constraintsApi()
             postApi()
+            announcementApi()
 
             // Web socket push notifications
             pushService()
diff --git a/src/jvmMain/kotlin/de/kif/backend/Configuration.kt b/src/jvmMain/kotlin/de/kif/backend/Configuration.kt
index 21ffe5e..eb7d7e3 100644
--- a/src/jvmMain/kotlin/de/kif/backend/Configuration.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/Configuration.kt
@@ -42,6 +42,7 @@ object Configuration {
         val sessions by required<String>()
         val uploads by required<String>()
         val database by required<String>()
+        val announcement by required<String>()
     }
 
     object Path {
@@ -56,6 +57,9 @@ object Configuration {
 
         val database by c(PathSpec.database)
         val databasePath: java.nio.file.Path by lazy { Paths.get(database).toAbsolutePath() }
+
+        val announcement by c(PathSpec.announcement)
+        val announcementPath: java.nio.file.Path by lazy { Paths.get(announcement).toAbsolutePath() }
     }
 
     private object ScheduleSpec : ConfigSpec("schedule") {
diff --git a/src/jvmMain/kotlin/de/kif/backend/repository/AnnouncementRepository.kt b/src/jvmMain/kotlin/de/kif/backend/repository/AnnouncementRepository.kt
new file mode 100644
index 0000000..af0a571
--- /dev/null
+++ b/src/jvmMain/kotlin/de/kif/backend/repository/AnnouncementRepository.kt
@@ -0,0 +1,53 @@
+package de.kif.backend.repository
+
+import de.kif.backend.Configuration
+import de.kif.backend.util.PushService
+import de.kif.common.MessageType
+import de.kif.common.RepositoryType
+import de.westermann.kobserve.event.EventHandler
+import kotlinx.coroutines.runBlocking
+
+object AnnouncementRepository {
+
+    val onUpdate = EventHandler<Unit>()
+
+    private val file = Configuration.Path.announcementPath.toFile()
+
+    private var announcement = ""
+
+    fun setAnnouncement(value: String) {
+        val str = value.replace("\n", " ").trim()
+        if (announcement == str) return
+
+        announcement = str
+        try {
+            file.writeText(str)
+        } catch (e: Exception) {
+
+        }
+
+        onUpdate.emit(Unit)
+    }
+
+    fun getAnnouncement(): String {
+        return announcement
+    }
+
+    fun registerPushService() {
+        onUpdate {
+            runBlocking {
+                PushService.notify(MessageType.UPDATE, RepositoryType.ANNOUNCEMENT, 0L)
+            }
+        }
+    }
+
+    init {
+        try {
+            if (!file.exists()) {
+                file.createNewFile()
+            }
+            announcement = file.readText().trim()
+        } catch (e: Exception) {
+        }
+    }
+}
diff --git a/src/jvmMain/kotlin/de/kif/backend/repository/WorkGroupRepository.kt b/src/jvmMain/kotlin/de/kif/backend/repository/WorkGroupRepository.kt
index a4ef155..46a1330 100644
--- a/src/jvmMain/kotlin/de/kif/backend/repository/WorkGroupRepository.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/repository/WorkGroupRepository.kt
@@ -3,10 +3,7 @@ package de.kif.backend.repository
 import de.kif.backend.database.DbWorkGroup
 import de.kif.backend.database.dbQuery
 import de.kif.backend.util.PushService
-import de.kif.common.Message
-import de.kif.common.MessageType
-import de.kif.common.Repository
-import de.kif.common.RepositoryType
+import de.kif.common.*
 import de.kif.common.model.Constraint
 import de.kif.common.model.WorkGroup
 import de.westermann.kobserve.event.EventHandler
@@ -36,8 +33,8 @@ object WorkGroupRepository : Repository<WorkGroup> {
         val accessible = row[DbWorkGroup.accessible]
         val length = row[DbWorkGroup.length]
         val language = row[DbWorkGroup.language]
-        val leader = Message.json.parse(String.serializer().list, row[DbWorkGroup.leader])
-        val constraints = Message.json.parse(Constraint.serializer().list, row[DbWorkGroup.constraints])
+        val leader = Serialization.parse(String.serializer().list, row[DbWorkGroup.leader])
+        val constraints = Serialization.parse(Constraint.serializer().list, row[DbWorkGroup.constraints])
 
         val createdAt = row[DbWorkGroup.createdAt]
         val updatedAt = row[DbWorkGroup.updatedAt]
@@ -92,8 +89,8 @@ object WorkGroupRepository : Repository<WorkGroup> {
                 it[accessible] = model.accessible
                 it[length] = model.length
                 it[language] = model.language
-                it[leader] = Message.json.stringify(String.serializer().list, model.leader)
-                it[constraints] = Message.json.stringify(Constraint.serializer().list, model.constraints)
+                it[leader] = Serialization.stringify(String.serializer().list, model.leader)
+                it[constraints] = Serialization.stringify(Constraint.serializer().list, model.constraints)
 
                 it[createdAt] = now
                 it[updatedAt] = now
@@ -124,8 +121,8 @@ object WorkGroupRepository : Repository<WorkGroup> {
                 it[accessible] = model.accessible
                 it[length] = model.length
                 it[language] = model.language
-                it[leader] = Message.json.stringify(String.serializer().list, model.leader)
-                it[constraints] = Message.json.stringify(Constraint.serializer().list, model.constraints)
+                it[leader] = Serialization.stringify(String.serializer().list, model.leader)
+                it[constraints] = Serialization.stringify(Constraint.serializer().list, model.constraints)
 
                 it[updatedAt] = now
             }
diff --git a/src/jvmMain/kotlin/de/kif/backend/route/Board.kt b/src/jvmMain/kotlin/de/kif/backend/route/Board.kt
index 14479d0..1407793 100644
--- a/src/jvmMain/kotlin/de/kif/backend/route/Board.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/route/Board.kt
@@ -1,6 +1,8 @@
 package de.kif.backend.route
 
 import de.kif.backend.Configuration
+import de.kif.backend.prefix
+import de.kif.backend.repository.AnnouncementRepository
 import de.kif.backend.repository.RoomRepository
 import de.kif.backend.repository.ScheduleRepository
 import de.kif.backend.view.respondMain
@@ -87,6 +89,18 @@ fun Route.board() {
         val nowLocale = now.time + timeOffset
         respondMain(true, true) { theme ->
             content {
+
+                val announcement = AnnouncementRepository.getAnnouncement()
+                var classes = "board-announcement announcement"
+                if (announcement.isBlank()) {
+                    classes += " announcement-blank"
+                }
+                div(classes) {
+                    span {
+                        +announcement
+                    }
+                }
+
                 div("board") {
                     div("board-header") {
                         div("board-running") {
@@ -142,7 +156,7 @@ fun Route.board() {
                             }
                         }
                         div("board-logo") {
-                            img("KIF 47.0", "/static/images/logo.svg")
+                            img("KIF 47.0", "$prefix/static/images/logo.svg")
                             div("board-header-date") {
                                 attributes["data-now"] = (now.time - timeOffset).toString()
                             }
diff --git a/src/jvmMain/kotlin/de/kif/backend/route/News.kt b/src/jvmMain/kotlin/de/kif/backend/route/News.kt
index ccb2aa6..4d3662b 100644
--- a/src/jvmMain/kotlin/de/kif/backend/route/News.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/route/News.kt
@@ -1,6 +1,7 @@
 package de.kif.backend.route
 
 import de.kif.backend.*
+import de.kif.backend.repository.AnnouncementRepository
 import de.kif.backend.repository.PostRepository
 import de.kif.backend.util.markdownToHtml
 import de.kif.backend.view.respondMain
@@ -13,11 +14,13 @@ import io.ktor.http.content.PartData
 import io.ktor.http.content.forEachPart
 import io.ktor.http.content.streamProvider
 import io.ktor.request.receiveMultipart
+import io.ktor.request.receiveParameters
 import io.ktor.response.respond
 import io.ktor.response.respondRedirect
 import io.ktor.routing.Route
 import io.ktor.routing.get
 import io.ktor.routing.post
+import io.ktor.util.toMap
 import kotlinx.html.*
 import java.io.File
 
@@ -75,9 +78,12 @@ fun Route.overview() {
             content {
                 if (editable) {
                     div("overview-new") {
-                        a("post/new", classes = "form-btn") {
+                        a("$prefix/post/new", classes = "form-btn") {
                             +"Neuer Eintrag"
                         }
+                        a("$prefix/announcement", classes = "form-btn") {
+                            +"Ankündigungsbanner bearbeiten"
+                        }
                     }
                 }
                 div("overview") {
@@ -133,7 +139,7 @@ fun Route.overview() {
     }
 
     get("/post/{id}") {
-        authenticateOrRedirect(Permission.POST) { user ->
+        authenticateOrRedirect(Permission.POST) {
             val postId = call.parameters["id"]?.toLongOrNull() ?: return@get
             val editPost = PostRepository.get(postId) ?: return@get
             respondMain {
@@ -291,7 +297,7 @@ fun Route.overview() {
     }
 
     post("/post/{id}") {
-        authenticateOrRedirect(Permission.POST) { user ->
+        authenticateOrRedirect(Permission.POST) {
             val postId = call.parameters["id"]?.toLongOrNull() ?: return@post
 
             var imageUploadName: String? = null
@@ -361,7 +367,7 @@ fun Route.overview() {
     }
 
     get("/post/new") {
-        authenticateOrRedirect(Permission.POST) { user ->
+        authenticateOrRedirect(Permission.POST) {
             respondMain {
                 content {
                     h1 { +"Beitrag erstellen" }
@@ -491,7 +497,7 @@ fun Route.overview() {
     }
 
     post("/post/new") {
-        authenticateOrRedirect(Permission.POST) { user ->
+        authenticateOrRedirect(Permission.POST) {
             var imageUploadName: String? = null
 
             val params = mutableMapOf<String, String>()
@@ -537,7 +543,7 @@ fun Route.overview() {
     }
 
     get("/post/{id}/delete") {
-        authenticateOrRedirect(Permission.POST) { user ->
+        authenticateOrRedirect(Permission.POST) {
             val postId = call.parameters["id"]?.toLongOrNull() ?: return@get
 
             PostRepository.delete(postId)
@@ -545,4 +551,57 @@ fun Route.overview() {
             call.respondRedirect("$prefix/")
         }
     }
+
+
+    get("/announcement") {
+        authenticateOrRedirect(Permission.POST) {
+            respondMain {
+                content {
+                    h1 { +"Ankündigungsbanner bearbeiten" }
+                            form(method = FormMethod.post) {
+                                div("form-group") {
+                                    label {
+                                        htmlFor = "announcement"
+                                        +"Ankündigung"
+                                    }
+                                    input(
+                                        name = "announcement",
+                                        classes = "form-control"
+                                    ) {
+                                        id = "announcement"
+                                        placeholder = "Ankündigung"
+                                        value = AnnouncementRepository.getAnnouncement()
+                                    }
+                                }
+
+                                div("form-group") {
+                                    a("$prefix/") {
+                                        button(classes = "form-btn") {
+                                            +"Abbrechen"
+                                        }
+                                    }
+                                    button(type = ButtonType.submit, classes = "form-btn btn-primary") {
+                                        +"Speichern"
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+
+
+    post("/announcement") {
+        authenticateOrRedirect(Permission.POST) {
+            val params = call.receiveParameters().toMap().mapValues { (_, list) ->
+                list.firstOrNull()
+            }
+
+            val announcement = params["announcement"] ?: return@post
+
+            AnnouncementRepository.setAnnouncement(announcement)
+
+            call.respondRedirect("$prefix/")
+        }
+    }
 }
diff --git a/src/jvmMain/kotlin/de/kif/backend/route/Room.kt b/src/jvmMain/kotlin/de/kif/backend/route/Room.kt
index ec8cad1..9d4cc55 100644
--- a/src/jvmMain/kotlin/de/kif/backend/route/Room.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/route/Room.kt
@@ -29,7 +29,7 @@ import de.kif.backend.prefix
 fun Route.room() {
 
     get("/rooms") {
-        authenticateOrRedirect(Permission.ROOM) { user ->
+        authenticateOrRedirect(Permission.ROOM) {
             val search = call.parameters["search"] ?: ""
             val list = RoomRepository.all()
 
@@ -106,7 +106,7 @@ fun Route.room() {
     }
 
     get("/room/{id}") {
-        authenticateOrRedirect(Permission.ROOM) { user ->
+        authenticateOrRedirect(Permission.ROOM) {
             val roomId = call.parameters["id"]?.toLongOrNull() ?: return@get
             val editRoom = RoomRepository.get(roomId) ?: return@get
             respondMain {
@@ -260,7 +260,7 @@ fun Route.room() {
     }
 
     post("/room/{id}") {
-        authenticateOrRedirect(Permission.ROOM) { user ->
+        authenticateOrRedirect(Permission.ROOM) {
             val roomId = call.parameters["id"]?.toLongOrNull() ?: return@post
             val params = call.receiveParameters().toMap().mapValues { (_, list) ->
                 list.firstOrNull()
@@ -283,7 +283,7 @@ fun Route.room() {
     }
 
     get("/room/new") {
-        authenticateOrRedirect(Permission.ROOM) { user ->
+        authenticateOrRedirect(Permission.ROOM) {
             respondMain {
                 content {
                     h1 { +"Raum erstellen" }
@@ -430,7 +430,7 @@ fun Route.room() {
     }
 
     post("/room/new") {
-        authenticateOrRedirect(Permission.ROOM) { user ->
+        authenticateOrRedirect(Permission.ROOM) {
             val params = call.receiveParameters().toMap().mapValues { (_, list) ->
                 list.firstOrNull()
             }
@@ -453,7 +453,7 @@ fun Route.room() {
     }
 
     get("/room/{id}/delete") {
-        authenticateOrRedirect(Permission.ROOM) { user ->
+        authenticateOrRedirect(Permission.ROOM) {
             val roomId = call.parameters["id"]?.toLongOrNull() ?: return@get
 
             RoomRepository.delete(roomId)
diff --git a/src/jvmMain/kotlin/de/kif/backend/route/Track.kt b/src/jvmMain/kotlin/de/kif/backend/route/Track.kt
index 81b9d35..15764fe 100644
--- a/src/jvmMain/kotlin/de/kif/backend/route/Track.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/route/Track.kt
@@ -83,7 +83,7 @@ fun DIV.colorPicker(color: Color?) {
 
 fun Route.track() {
     get("/tracks") {
-        authenticateOrRedirect(Permission.WORK_GROUP) { user ->
+        authenticateOrRedirect(Permission.WORK_GROUP) {
             val search = call.parameters["search"] ?: ""
             val list = TrackRepository.all()
             respondMain {
@@ -145,7 +145,7 @@ fun Route.track() {
     }
 
     get("/track/{id}") {
-        authenticateOrRedirect(Permission.WORK_GROUP) { user ->
+        authenticateOrRedirect(Permission.WORK_GROUP) {
             val trackId = call.parameters["id"]?.toLongOrNull() ?: return@get
             val editTrack = TrackRepository.get(trackId) ?: return@get
             respondMain {
@@ -192,7 +192,7 @@ fun Route.track() {
     }
 
     post("/track/{id}") {
-        authenticateOrRedirect(Permission.WORK_GROUP) { user ->
+        authenticateOrRedirect(Permission.WORK_GROUP) {
             val trackId = call.parameters["id"]?.toLongOrNull() ?: return@post
             val params = call.receiveParameters().toMap().mapValues { (_, list) ->
                 list.firstOrNull()
@@ -212,7 +212,7 @@ fun Route.track() {
     }
 
     get("/track/new") {
-        authenticateOrRedirect(Permission.WORK_GROUP) { user ->
+        authenticateOrRedirect(Permission.WORK_GROUP) {
             respondMain {
                 content {
                     h1 { +"Track erstellen" }
@@ -251,7 +251,7 @@ fun Route.track() {
     }
 
     post("/track/new") {
-        authenticateOrRedirect(Permission.WORK_GROUP) { user ->
+        authenticateOrRedirect(Permission.WORK_GROUP) {
             val params = call.receiveParameters().toMap().mapValues { (_, list) ->
                 list.firstOrNull()
             }
@@ -270,7 +270,7 @@ fun Route.track() {
     }
 
     get("track/{id}/delete") {
-        authenticateOrRedirect(Permission.WORK_GROUP) { user ->
+        authenticateOrRedirect(Permission.WORK_GROUP) {
             val trackId = call.parameters["id"]?.toLongOrNull() ?: return@get
 
             TrackRepository.delete(trackId)
diff --git a/src/jvmMain/kotlin/de/kif/backend/route/User.kt b/src/jvmMain/kotlin/de/kif/backend/route/User.kt
index a301f1d..2f589f3 100644
--- a/src/jvmMain/kotlin/de/kif/backend/route/User.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/route/User.kt
@@ -26,8 +26,8 @@ import kotlin.collections.component2
 import kotlin.collections.set
 
 fun Route.user() {
-    get("/users") { param ->
-        authenticateOrRedirect(Permission.USER) { user ->
+    get("/users") {
+        authenticateOrRedirect(Permission.USER) {
             val search = call.parameters["search"] ?: ""
             val list = UserRepository.all()
             respondMain {
diff --git a/src/jvmMain/kotlin/de/kif/backend/route/WorkGroup.kt b/src/jvmMain/kotlin/de/kif/backend/route/WorkGroup.kt
index 0957c4b..9c90782 100644
--- a/src/jvmMain/kotlin/de/kif/backend/route/WorkGroup.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/route/WorkGroup.kt
@@ -25,7 +25,7 @@ private const val separator = "###"
 
 fun Route.workGroup() {
     get("workgroups") {
-        authenticateOrRedirect(Permission.WORK_GROUP) { user ->
+        authenticateOrRedirect(Permission.WORK_GROUP) {
             val search = call.parameters["search"] ?: ""
             val list = WorkGroupRepository.all()
             respondMain {
@@ -146,7 +146,7 @@ fun Route.workGroup() {
     }
 
     get("/workgroup/{id}") {
-        authenticateOrRedirect(Permission.WORK_GROUP) { user ->
+        authenticateOrRedirect(Permission.WORK_GROUP) {
             val workGroupId = call.parameters["id"]?.toLongOrNull() ?: return@get
             val editWorkGroup = WorkGroupRepository.get(workGroupId) ?: return@get
             val tracks = TrackRepository.all()
@@ -532,7 +532,7 @@ fun Route.workGroup() {
     }
 
     post("/workgroup/{id}") {
-        authenticateOrRedirect(Permission.WORK_GROUP) { user ->
+        authenticateOrRedirect(Permission.WORK_GROUP) {
             val workGroupId = call.parameters["id"]?.toLongOrNull() ?: return@post
             val params = call.receiveParameters().toMap().mapValues { (_, list) ->
                 list.firstOrNull()
@@ -574,7 +574,7 @@ fun Route.workGroup() {
     }
 
     get("/workgroup/new") {
-        authenticateOrRedirect(Permission.WORK_GROUP) { user ->
+        authenticateOrRedirect(Permission.WORK_GROUP) {
             val tracks = TrackRepository.all()
             respondMain {
                 content {
@@ -823,7 +823,7 @@ fun Route.workGroup() {
     }
 
     post("/workgroup/new") {
-        authenticateOrRedirect(Permission.WORK_GROUP) { user ->
+        authenticateOrRedirect(Permission.WORK_GROUP) {
             val params = call.receiveParameters().toMap().mapValues { (_, list) ->
                 list.firstOrNull()
             }
@@ -872,7 +872,7 @@ fun Route.workGroup() {
     }
 
     get("/workgroup/{id}/delete") {
-        authenticateOrRedirect(Permission.WORK_GROUP) { user ->
+        authenticateOrRedirect(Permission.WORK_GROUP) {
             val workGroupId = call.parameters["id"]?.toLongOrNull() ?: return@get
 
             WorkGroupRepository.delete(workGroupId)
diff --git a/src/jvmMain/kotlin/de/kif/backend/route/api/Announcement.kt b/src/jvmMain/kotlin/de/kif/backend/route/api/Announcement.kt
new file mode 100644
index 0000000..938e94e
--- /dev/null
+++ b/src/jvmMain/kotlin/de/kif/backend/route/api/Announcement.kt
@@ -0,0 +1,39 @@
+package de.kif.backend.route.api
+
+import de.kif.backend.authenticate
+import de.kif.backend.repository.AnnouncementRepository
+import de.kif.backend.repository.RoomRepository
+import de.kif.common.model.Permission
+import de.kif.common.model.Room
+import io.ktor.application.call
+import io.ktor.http.HttpStatusCode
+import io.ktor.request.receive
+import io.ktor.routing.Route
+import io.ktor.routing.get
+import io.ktor.routing.post
+
+fun Route.announcementApi() {
+    get("/api/announcement") {
+        try {
+            call.success(AnnouncementRepository.getAnnouncement())
+        } catch (_: Exception) {
+            call.error(HttpStatusCode.InternalServerError)
+        }
+    }
+
+    post("/api/announcement") {
+        try {
+            authenticate(Permission.POST) {
+                val announcement = call.receive<String>()
+
+                AnnouncementRepository.setAnnouncement(announcement)
+
+                call.success()
+            } onFailure {
+                call.error(HttpStatusCode.Unauthorized)
+            }
+        } catch (_: Exception) {
+            call.error(HttpStatusCode.InternalServerError)
+        }
+    }
+}
diff --git a/src/jvmMain/kotlin/de/kif/backend/util/Backup.kt b/src/jvmMain/kotlin/de/kif/backend/util/Backup.kt
index b9f758f..21c0c8d 100644
--- a/src/jvmMain/kotlin/de/kif/backend/util/Backup.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/util/Backup.kt
@@ -4,6 +4,7 @@ import de.kif.backend.database.Connection
 import de.kif.backend.repository.*
 import de.kif.common.Message
 import de.kif.common.RepositoryType
+import de.kif.common.Serialization
 import de.kif.common.model.*
 import kotlinx.serialization.Serializable
 
@@ -39,15 +40,16 @@ data class Backup(
                     RepositoryType.USER -> backup.copy(users = UserRepository.all())
                     RepositoryType.WORK_GROUP -> backup.copy(workGroups = WorkGroupRepository.all())
                     RepositoryType.POST -> backup.copy(posts = PostRepository.all())
+                    else -> backup
                 }
             }
 
-            return Message.json.stringify(serializer(), backup)
+            return Serialization.stringify(serializer(), backup)
         }
 
         @Suppress("UNUSED_VARIABLE")
         suspend fun import(data: String) {
-            val backup = Message.json.parse(serializer(), data)
+            val backup = Serialization.parse(serializer(), data)
 
             backup.users.forEach { UserRepository.create(it); println("Import user ${it.username}") }
             backup.posts.forEach { PostRepository.create(it); println("Import post") }
diff --git a/src/jvmMain/kotlin/de/kif/backend/util/PushService.kt b/src/jvmMain/kotlin/de/kif/backend/util/PushService.kt
index 12f07e3..78c7127 100644
--- a/src/jvmMain/kotlin/de/kif/backend/util/PushService.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/util/PushService.kt
@@ -1,48 +1,60 @@
 package de.kif.backend.util
 
-import de.kif.backend.prefix
 import de.kif.backend.repository.*
-import de.kif.common.*
+import de.kif.backend.route.api.error
+import de.kif.backend.route.api.success
+import de.kif.common.Message
+import de.kif.common.MessageBox
+import de.kif.common.MessageType
 import de.kif.common.RepositoryType
-import io.ktor.http.cio.websocket.Frame
-import io.ktor.http.cio.websocket.readText
+import io.ktor.application.call
+import io.ktor.http.HttpStatusCode
 import io.ktor.routing.Route
-import io.ktor.websocket.WebSocketServerSession
-import io.ktor.websocket.webSocket
-import kotlinx.coroutines.channels.ClosedReceiveChannelException
+import io.ktor.routing.get
 
 object PushService {
 
-    var clients: List<WebSocketServerSession> = emptyList()
+    var leastValidTimestamp = System.currentTimeMillis()
 
-    suspend fun notify(type: MessageType, repository: RepositoryType, id: Long) {
-        try {
-            val data = Message(type, repository, id).stringify()
-            for (client in clients) {
-                client.outgoing.send(Frame.Text(data))
-            }
-        } catch (e: Exception) {
-            e.printStackTrace()
-        }
+    /**
+     * Save the message with the current timestamp
+     */
+    fun notify(type: MessageType, repository: RepositoryType, id: Long) {
+        val timestamp = System.currentTimeMillis()
+        val message = Message(type, repository, id)
+    }
+
+    /**
+     * Get all messages created after the given timestamp.
+     * The return Box has the current timestamp. If the leastValidTimestamp is less then the current timestamp set the
+     * valid flag to false and return an empty message list.
+     */
+    fun getMessages(timestamp: Long?): MessageBox {
+        return MessageBox(
+            System.currentTimeMillis(),
+            timestamp != null && timestamp > leastValidTimestamp,
+            emptyList()
+        )
+    }
+
+    /**
+     * Delete all messages before the given timestamp
+     */
+    fun gc(timestamp: Long) {
+        leastValidTimestamp = timestamp
     }
 }
 
 fun Route.pushService() {
-    webSocket("/websocket") {
-        PushService.clients += this
-
+    get("/api/updates") {
         try {
-            while (true) {
-                val text = (incoming.receive() as Frame.Text).readText()
-                println("onMessage($text)")
-                outgoing.send(Frame.Text(text))
-            }
-        } catch (_: ClosedReceiveChannelException) {
-            PushService.clients -= this
-        } catch (e: Throwable) {
-            println("onFailure ${closeReason.await()}")
-            e.printStackTrace()
-            PushService.clients -= this
+            val timestamp = call.request.queryParameters["timestamp"]?.toLongOrNull()
+
+            val messageBox = PushService.getMessages(timestamp)
+
+            call.success(messageBox)
+        } catch (_: Exception) {
+            call.error(HttpStatusCode.InternalServerError)
         }
     }
 
@@ -52,4 +64,5 @@ fun Route.pushService() {
     UserRepository.registerPushService()
     WorkGroupRepository.registerPushService()
     PostRepository.registerPushService()
+    AnnouncementRepository.registerPushService()
 }
diff --git a/src/jvmMain/kotlin/de/kif/backend/view/MainTemplate.kt b/src/jvmMain/kotlin/de/kif/backend/view/MainTemplate.kt
index f96a52e..3f8271e 100644
--- a/src/jvmMain/kotlin/de/kif/backend/view/MainTemplate.kt
+++ b/src/jvmMain/kotlin/de/kif/backend/view/MainTemplate.kt
@@ -3,6 +3,7 @@ package de.kif.backend.view
 import de.kif.backend.PortalSession
 import de.kif.backend.Resources
 import de.kif.backend.prefix
+import de.kif.backend.repository.AnnouncementRepository
 import de.kif.common.model.User
 import io.ktor.application.ApplicationCall
 import io.ktor.application.call
@@ -73,10 +74,25 @@ class MainTemplate(
             }
         }
         body {
+            attributes["data-timestamp"] = currentTimeMillis().toString()
+
             if (!noMenu) {
                 insert(MenuTemplate(url, user)) {}
             }
 
+            if (!noMenu) {
+                val announcement = AnnouncementRepository.getAnnouncement()
+                var classes = "announcement"
+                if (announcement.isBlank()) {
+                    classes += " announcement-blank"
+                }
+                div(classes) {
+                    span {
+                        +announcement
+                    }
+                }
+            }
+
             val containerClasses = if (stretch) "container-full" else "container"
             div(containerClasses) {
                 div("main") {
@@ -84,6 +100,10 @@ class MainTemplate(
                 }
             }
 
+            div("offline-banner") {
+                span { +"Die Verbindung zum Server ist unterbrochen" }
+            }
+
             if (!noMenu) {
                 div("footer") {
                     div("container") {
diff --git a/src/jvmMain/resources/portal.toml b/src/jvmMain/resources/portal.toml
index 02fc07d..28f8096 100644
--- a/src/jvmMain/resources/portal.toml
+++ b/src/jvmMain/resources/portal.toml
@@ -9,6 +9,7 @@ web = "web"
 sessions = "data/sessions"
 uploads = "data/uploads"
 database = "data/portal.db"
+announcement = "data/announcement.txt"
 
 [schedule]
 reference = "1970-01-01"