diff --git a/crates/modbusmaster-app/src/update.rs b/crates/modbusmaster-app/src/update.rs
index 8592b8b..960f4a6 100644
--- a/crates/modbusmaster-app/src/update.rs
+++ b/crates/modbusmaster-app/src/update.rs
@@ -1,15 +1,26 @@
 use chrono::{DateTime, Duration, Utc};
 use serde::Serialize;
-use tauri::{AppHandle, Manager, State};
+use std::sync::{
+    atomic::{AtomicU64, Ordering},
+    Arc,
+};
+use std::time::Duration as StdDuration;
+use tauri::{AppHandle, Emitter, Manager, State};
 use tauri_plugin_store::StoreExt;
 use tauri_plugin_updater::{Update, UpdaterExt};
-use tokio::sync::Mutex;
+use tokio::{sync::Mutex, time::timeout};
 
 const STORE_FILE: &str = "update_state.json";
 const KEY_LAST_CHECK: &str = "last_check_at";
 const KEY_SKIPPED_VERSION: &str = "skipped_version";
 const KEY_INSTALL_ON_NEXT_LAUNCH: &str = "install_on_next_launch";
 const THROTTLE_HOURS: i64 = 6;
+const CHECK_ENDPOINT_TIMEOUT: StdDuration = StdDuration::from_secs(10);
+const CHECK_TOTAL_TIMEOUT: StdDuration = StdDuration::from_secs(30);
+const DOWNLOAD_TIMEOUT: StdDuration = StdDuration::from_secs(5 * 60);
+const PROGRESS_EVENT: &str = "update-progress";
+const CHECK_TIMEOUT_ERROR: &str = "UPDATE_CHECK_TIMEOUT";
+const DOWNLOAD_TIMEOUT_ERROR: &str = "UPDATE_DOWNLOAD_TIMEOUT";
 
 #[derive(Serialize, Clone)]
 pub struct UpdateMeta {
@@ -18,6 +29,14 @@ pub struct UpdateMeta {
     pub pub_date: Option<String>,
 }
 
+#[derive(Serialize, Clone)]
+struct UpdateProgress {
+    stage: &'static str,
+    downloaded: u64,
+    total: Option<u64>,
+    percent: Option<u8>,
+}
+
 struct PreparedUpdate {
     meta: UpdateMeta,
     update: Update,
@@ -75,14 +94,92 @@ fn update_meta(update: &Update) -> UpdateMeta {
     }
 }
 
-async fn download_update(update: &Update) -> Result<Vec<u8>, String> {
-    update
-        .download(
-            |_, _| {},
-            || log::info!("update download finished; verifying release signature"),
-        )
-        .await
-        .map_err(|e| e.to_string())
+fn progress_percent(downloaded: u64, total: Option<u64>) -> Option<u8> {
+    total
+        .filter(|total| *total > 0)
+        .map(|total| ((downloaded.saturating_mul(100) / total).min(100)) as u8)
+}
+
+fn emit_update_progress(app: &AppHandle, stage: &'static str, downloaded: u64, total: Option<u64>) {
+    let _ = app.emit(
+        PROGRESS_EVENT,
+        UpdateProgress {
+            stage,
+            downloaded,
+            total,
+            percent: progress_percent(downloaded, total),
+        },
+    );
+}
+
+async fn find_update(app: &AppHandle) -> Result<Option<Update>, String> {
+    emit_update_progress(app, "checking", 0, None);
+    let result = async {
+        let updater = app
+            .updater_builder()
+            .timeout(CHECK_ENDPOINT_TIMEOUT)
+            .build()
+            .map_err(|e| e.to_string())?;
+        timeout(CHECK_TOTAL_TIMEOUT, updater.check())
+            .await
+            .map_err(|_| CHECK_TIMEOUT_ERROR.to_string())?
+            .map_err(|e| e.to_string())
+    }
+    .await;
+    if result.is_err() {
+        emit_update_progress(app, "idle", 0, None);
+    }
+    result
+}
+
+async fn download_update(app: &AppHandle, update: &Update) -> Result<Vec<u8>, String> {
+    emit_update_progress(app, "downloading", 0, None);
+    let progress_app = app.clone();
+    let verify_app = app.clone();
+    let downloaded = Arc::new(AtomicU64::new(0));
+    let progress_downloaded = Arc::clone(&downloaded);
+    let verify_downloaded = Arc::clone(&downloaded);
+    let mut last_percent = None;
+    let mut last_emitted_bytes = 0_u64;
+    let download = update.download(
+        move |chunk_len, total| {
+            let downloaded = progress_downloaded
+                .fetch_add(chunk_len as u64, Ordering::Relaxed)
+                .saturating_add(chunk_len as u64);
+            let percent = progress_percent(downloaded, total);
+            let should_emit = percent != last_percent
+                || (total.is_none() && downloaded.saturating_sub(last_emitted_bytes) >= 256 * 1024);
+            if should_emit {
+                emit_update_progress(&progress_app, "downloading", downloaded, total);
+                last_percent = percent;
+                last_emitted_bytes = downloaded;
+            }
+        },
+        move || {
+            emit_update_progress(
+                &verify_app,
+                "verifying",
+                verify_downloaded.load(Ordering::Relaxed),
+                None,
+            );
+            log::info!("update download finished; verifying release signature");
+        },
+    );
+
+    let result = match timeout(DOWNLOAD_TIMEOUT, download).await {
+        Ok(result) => result.map_err(|e| e.to_string()),
+        Err(_) => Err(DOWNLOAD_TIMEOUT_ERROR.to_string()),
+    };
+    match result {
+        Ok(bytes) => {
+            emit_update_progress(app, "ready", bytes.len() as u64, Some(bytes.len() as u64));
+            Ok(bytes)
+        }
+        Err(error) => {
+            emit_update_progress(app, "idle", 0, None);
+            Err(error)
+        }
+    }
 }
 
 #[tauri::command]
@@ -98,6 +195,12 @@ pub async fn check_for_update(
 
     let mut prepared = state.prepared.lock().await;
     if let Some(update) = prepared.as_ref() {
+        emit_update_progress(
+            &app,
+            "ready",
+            update.bytes.len() as u64,
+            Some(update.bytes.len() as u64),
+        );
         return Ok(Some(update.meta.clone()));
     }
 
@@ -105,13 +208,14 @@ pub async fn check_for_update(
     if !force {
         let last = parse_ts(read_str(&app, KEY_LAST_CHECK));
         if !should_check(last, now, Duration::hours(THROTTLE_HOURS)) {
+            emit_update_progress(&app, "idle", 0, None);
             return Ok(None);
         }
     }
     write_str(&app, KEY_LAST_CHECK, &now.to_rfc3339());
 
-    let updater = app.updater().map_err(|e| e.to_string())?;
-    let Some(update) = updater.check().await.map_err(|e| e.to_string())? else {
+    let Some(update) = find_update(&app).await? else {
+        emit_update_progress(&app, "idle", 0, None);
         return Ok(None);
     };
     if !force
@@ -120,11 +224,12 @@ pub async fn check_for_update(
             &update.version,
         )
     {
+        emit_update_progress(&app, "idle", 0, None);
         return Ok(None);
     }
 
     let meta = update_meta(&update);
-    let bytes = download_update(&update).await?;
+    let bytes = download_update(&app, &update).await?;
     *prepared = Some(PreparedUpdate {
         meta: meta.clone(),
         update,
@@ -193,13 +298,13 @@ pub async fn install_pending_update(app: AppHandle) -> Result<(), String> {
 
     let state = app.state::<UpdateState>();
     let mut prepared = state.prepared.lock().await;
-    let updater = app.updater().map_err(|e| e.to_string())?;
-    let Some(update) = updater.check().await.map_err(|e| e.to_string())? else {
+    let Some(update) = find_update(&app).await? else {
+        emit_update_progress(&app, "idle", 0, None);
         remove_value(&app, KEY_INSTALL_ON_NEXT_LAUNCH);
         return Ok(());
     };
     let meta = update_meta(&update);
-    let bytes = download_update(&update).await?;
+    let bytes = download_update(&app, &update).await?;
     *prepared = Some(PreparedUpdate {
         meta,
         update,
@@ -232,3 +337,20 @@ pub fn should_check(
 pub fn is_skipped(skipped_version: Option<&str>, remote_version: &str) -> bool {
     skipped_version == Some(remote_version)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::progress_percent;
+
+    #[test]
+    fn progress_requires_a_non_zero_total() {
+        assert_eq!(progress_percent(25, None), None);
+        assert_eq!(progress_percent(25, Some(0)), None);
+    }
+
+    #[test]
+    fn progress_is_an_integer_percentage_capped_at_100() {
+        assert_eq!(progress_percent(25, Some(100)), Some(25));
+        assert_eq!(progress_percent(200, Some(100)), Some(100));
+    }
+}
diff --git a/crates/modbussim-app/src/update.rs b/crates/modbussim-app/src/update.rs
index 8592b8b..960f4a6 100644
--- a/crates/modbussim-app/src/update.rs
+++ b/crates/modbussim-app/src/update.rs
@@ -1,15 +1,26 @@
 use chrono::{DateTime, Duration, Utc};
 use serde::Serialize;
-use tauri::{AppHandle, Manager, State};
+use std::sync::{
+    atomic::{AtomicU64, Ordering},
+    Arc,
+};
+use std::time::Duration as StdDuration;
+use tauri::{AppHandle, Emitter, Manager, State};
 use tauri_plugin_store::StoreExt;
 use tauri_plugin_updater::{Update, UpdaterExt};
-use tokio::sync::Mutex;
+use tokio::{sync::Mutex, time::timeout};
 
 const STORE_FILE: &str = "update_state.json";
 const KEY_LAST_CHECK: &str = "last_check_at";
 const KEY_SKIPPED_VERSION: &str = "skipped_version";
 const KEY_INSTALL_ON_NEXT_LAUNCH: &str = "install_on_next_launch";
 const THROTTLE_HOURS: i64 = 6;
+const CHECK_ENDPOINT_TIMEOUT: StdDuration = StdDuration::from_secs(10);
+const CHECK_TOTAL_TIMEOUT: StdDuration = StdDuration::from_secs(30);
+const DOWNLOAD_TIMEOUT: StdDuration = StdDuration::from_secs(5 * 60);
+const PROGRESS_EVENT: &str = "update-progress";
+const CHECK_TIMEOUT_ERROR: &str = "UPDATE_CHECK_TIMEOUT";
+const DOWNLOAD_TIMEOUT_ERROR: &str = "UPDATE_DOWNLOAD_TIMEOUT";
 
 #[derive(Serialize, Clone)]
 pub struct UpdateMeta {
@@ -18,6 +29,14 @@ pub struct UpdateMeta {
     pub pub_date: Option<String>,
 }
 
+#[derive(Serialize, Clone)]
+struct UpdateProgress {
+    stage: &'static str,
+    downloaded: u64,
+    total: Option<u64>,
+    percent: Option<u8>,
+}
+
 struct PreparedUpdate {
     meta: UpdateMeta,
     update: Update,
@@ -75,14 +94,92 @@ fn update_meta(update: &Update) -> UpdateMeta {
     }
 }
 
-async fn download_update(update: &Update) -> Result<Vec<u8>, String> {
-    update
-        .download(
-            |_, _| {},
-            || log::info!("update download finished; verifying release signature"),
-        )
-        .await
-        .map_err(|e| e.to_string())
+fn progress_percent(downloaded: u64, total: Option<u64>) -> Option<u8> {
+    total
+        .filter(|total| *total > 0)
+        .map(|total| ((downloaded.saturating_mul(100) / total).min(100)) as u8)
+}
+
+fn emit_update_progress(app: &AppHandle, stage: &'static str, downloaded: u64, total: Option<u64>) {
+    let _ = app.emit(
+        PROGRESS_EVENT,
+        UpdateProgress {
+            stage,
+            downloaded,
+            total,
+            percent: progress_percent(downloaded, total),
+        },
+    );
+}
+
+async fn find_update(app: &AppHandle) -> Result<Option<Update>, String> {
+    emit_update_progress(app, "checking", 0, None);
+    let result = async {
+        let updater = app
+            .updater_builder()
+            .timeout(CHECK_ENDPOINT_TIMEOUT)
+            .build()
+            .map_err(|e| e.to_string())?;
+        timeout(CHECK_TOTAL_TIMEOUT, updater.check())
+            .await
+            .map_err(|_| CHECK_TIMEOUT_ERROR.to_string())?
+            .map_err(|e| e.to_string())
+    }
+    .await;
+    if result.is_err() {
+        emit_update_progress(app, "idle", 0, None);
+    }
+    result
+}
+
+async fn download_update(app: &AppHandle, update: &Update) -> Result<Vec<u8>, String> {
+    emit_update_progress(app, "downloading", 0, None);
+    let progress_app = app.clone();
+    let verify_app = app.clone();
+    let downloaded = Arc::new(AtomicU64::new(0));
+    let progress_downloaded = Arc::clone(&downloaded);
+    let verify_downloaded = Arc::clone(&downloaded);
+    let mut last_percent = None;
+    let mut last_emitted_bytes = 0_u64;
+    let download = update.download(
+        move |chunk_len, total| {
+            let downloaded = progress_downloaded
+                .fetch_add(chunk_len as u64, Ordering::Relaxed)
+                .saturating_add(chunk_len as u64);
+            let percent = progress_percent(downloaded, total);
+            let should_emit = percent != last_percent
+                || (total.is_none() && downloaded.saturating_sub(last_emitted_bytes) >= 256 * 1024);
+            if should_emit {
+                emit_update_progress(&progress_app, "downloading", downloaded, total);
+                last_percent = percent;
+                last_emitted_bytes = downloaded;
+            }
+        },
+        move || {
+            emit_update_progress(
+                &verify_app,
+                "verifying",
+                verify_downloaded.load(Ordering::Relaxed),
+                None,
+            );
+            log::info!("update download finished; verifying release signature");
+        },
+    );
+
+    let result = match timeout(DOWNLOAD_TIMEOUT, download).await {
+        Ok(result) => result.map_err(|e| e.to_string()),
+        Err(_) => Err(DOWNLOAD_TIMEOUT_ERROR.to_string()),
+    };
+    match result {
+        Ok(bytes) => {
+            emit_update_progress(app, "ready", bytes.len() as u64, Some(bytes.len() as u64));
+            Ok(bytes)
+        }
+        Err(error) => {
+            emit_update_progress(app, "idle", 0, None);
+            Err(error)
+        }
+    }
 }
 
 #[tauri::command]
@@ -98,6 +195,12 @@ pub async fn check_for_update(
 
     let mut prepared = state.prepared.lock().await;
     if let Some(update) = prepared.as_ref() {
+        emit_update_progress(
+            &app,
+            "ready",
+            update.bytes.len() as u64,
+            Some(update.bytes.len() as u64),
+        );
         return Ok(Some(update.meta.clone()));
     }
 
@@ -105,13 +208,14 @@ pub async fn check_for_update(
     if !force {
         let last = parse_ts(read_str(&app, KEY_LAST_CHECK));
         if !should_check(last, now, Duration::hours(THROTTLE_HOURS)) {
+            emit_update_progress(&app, "idle", 0, None);
             return Ok(None);
         }
     }
     write_str(&app, KEY_LAST_CHECK, &now.to_rfc3339());
 
-    let updater = app.updater().map_err(|e| e.to_string())?;
-    let Some(update) = updater.check().await.map_err(|e| e.to_string())? else {
+    let Some(update) = find_update(&app).await? else {
+        emit_update_progress(&app, "idle", 0, None);
         return Ok(None);
     };
     if !force
@@ -120,11 +224,12 @@ pub async fn check_for_update(
             &update.version,
         )
     {
+        emit_update_progress(&app, "idle", 0, None);
         return Ok(None);
     }
 
     let meta = update_meta(&update);
-    let bytes = download_update(&update).await?;
+    let bytes = download_update(&app, &update).await?;
     *prepared = Some(PreparedUpdate {
         meta: meta.clone(),
         update,
@@ -193,13 +298,13 @@ pub async fn install_pending_update(app: AppHandle) -> Result<(), String> {
 
     let state = app.state::<UpdateState>();
     let mut prepared = state.prepared.lock().await;
-    let updater = app.updater().map_err(|e| e.to_string())?;
-    let Some(update) = updater.check().await.map_err(|e| e.to_string())? else {
+    let Some(update) = find_update(&app).await? else {
+        emit_update_progress(&app, "idle", 0, None);
         remove_value(&app, KEY_INSTALL_ON_NEXT_LAUNCH);
         return Ok(());
     };
     let meta = update_meta(&update);
-    let bytes = download_update(&update).await?;
+    let bytes = download_update(&app, &update).await?;
     *prepared = Some(PreparedUpdate {
         meta,
         update,
@@ -232,3 +337,20 @@ pub fn should_check(
 pub fn is_skipped(skipped_version: Option<&str>, remote_version: &str) -> bool {
     skipped_version == Some(remote_version)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::progress_percent;
+
+    #[test]
+    fn progress_requires_a_non_zero_total() {
+        assert_eq!(progress_percent(25, None), None);
+        assert_eq!(progress_percent(25, Some(0)), None);
+    }
+
+    #[test]
+    fn progress_is_an_integer_percentage_capped_at_100() {
+        assert_eq!(progress_percent(25, Some(100)), Some(25));
+        assert_eq!(progress_percent(200, Some(100)), Some(100));
+    }
+}
diff --git a/frontend/src/components/Toolbar.vue b/frontend/src/components/Toolbar.vue
index c42bdfb..5099bca 100644
--- a/frontend/src/components/Toolbar.vue
+++ b/frontend/src/components/Toolbar.vue
@@ -1,8 +1,16 @@
 <script setup lang="ts">
-import { ref, inject, type Ref } from 'vue'
+import { computed, ref, inject, type Ref } from 'vue'
 import { invoke } from '@tauri-apps/api/core'
 import { save, open } from '@tauri-apps/plugin-dialog'
-import { useI18n, LangToggle, VersionBadge, showAlert, showConfirm } from 'shared-frontend'
+import {
+  useI18n,
+  useUpdateProgress,
+  localizeUpdateError,
+  LangToggle,
+  VersionBadge,
+  showAlert,
+  showConfirm,
+} from 'shared-frontend'
 import NewConnectionDialog from './NewConnectionDialog.vue'
 import NewSlaveDialog from './NewSlaveDialog.vue'
 import MutationControl from './MutationControl.vue'
@@ -23,18 +31,29 @@ const mutationControlKey = ref(0)
 type UpdateMeta = { version: string; notes: string; pub_date?: string | null }
 const checkUpdate = inject<(force?: boolean) => Promise<UpdateMeta | null>>('checkUpdate')!
 const updateChecking = ref(false)
+const updateProgress = useUpdateProgress(t)
+const updateBusy = computed(() => updateChecking.value || updateProgress.active.value)
+const updateButtonLabel = computed(() =>
+  updateProgress.active.value
+    ? updateProgress.label.value
+    : updateChecking.value
+      ? t('toolbar.checkingUpdate')
+      : t('toolbar.checkUpdate'),
+)
 
 async function manualCheckUpdate() {
-  if (updateChecking.value) return
+  if (updateBusy.value) return
   updateChecking.value = true
+  let message: string | null = null
   try {
     const meta = await checkUpdate(true)
-    if (!meta) await showAlert(t('toolbar.alreadyLatest'))
+    if (!meta) message = t('toolbar.alreadyLatest')
   } catch (e) {
-    await showAlert(`${t('toolbar.updateCheckFailed')}: ${e}`)
+    message = `${t('toolbar.updateCheckFailed')}: ${localizeUpdateError(e, t)}`
   } finally {
     updateChecking.value = false
   }
+  if (message) await showAlert(message)
 }
 
 async function openProject() {
@@ -176,8 +195,8 @@ async function openTools() {
       </button>
     </div>
     <div class="toolbar-spacer" style="flex:1"></div>
-    <button class="toolbar-btn" :disabled="updateChecking" @click="manualCheckUpdate">
-      <span class="toolbar-label">{{ updateChecking ? t('toolbar.checkingUpdate') : t('toolbar.checkUpdate') }}</span>
+    <button class="toolbar-btn" :disabled="updateBusy" @click="manualCheckUpdate">
+      <span class="toolbar-label" aria-live="polite">{{ updateButtonLabel }}</span>
     </button>
     <LangToggle />
     <VersionBadge />
diff --git a/master-frontend/src/components/Toolbar.vue b/master-frontend/src/components/Toolbar.vue
index 7a44c0f..1bdd364 100644
--- a/master-frontend/src/components/Toolbar.vue
+++ b/master-frontend/src/components/Toolbar.vue
@@ -1,8 +1,16 @@
 <script setup lang="ts">
-import { inject, ref, type Ref } from 'vue'
+import { computed, inject, ref, type Ref } from 'vue'
 import { invoke } from '@tauri-apps/api/core'
 import { save, open } from '@tauri-apps/plugin-dialog'
-import { useI18n, LangToggle, VersionBadge, showAlert, showConfirm } from 'shared-frontend'
+import {
+  useI18n,
+  useUpdateProgress,
+  localizeUpdateError,
+  LangToggle,
+  VersionBadge,
+  showAlert,
+  showConfirm,
+} from 'shared-frontend'
 import ScanDialog from './ScanDialog.vue'
 import NewConnectionDialog from './NewConnectionDialog.vue'
 import NewScanGroupDialog from './NewScanGroupDialog.vue'
@@ -23,18 +31,29 @@ const showScanDialog = ref(false)
 type UpdateMeta = { version: string; notes: string; pub_date?: string | null }
 const checkUpdate = inject<(force?: boolean) => Promise<UpdateMeta | null>>('checkUpdate')!
 const updateChecking = ref(false)
+const updateProgress = useUpdateProgress(t)
+const updateBusy = computed(() => updateChecking.value || updateProgress.active.value)
+const updateButtonLabel = computed(() =>
+  updateProgress.active.value
+    ? updateProgress.label.value
+    : updateChecking.value
+      ? t('toolbar.checkingUpdate')
+      : t('toolbar.checkUpdate'),
+)
 
 async function manualCheckUpdate() {
-  if (updateChecking.value) return
+  if (updateBusy.value) return
   updateChecking.value = true
+  let message: string | null = null
   try {
     const meta = await checkUpdate(true)
-    if (!meta) await showAlert(t('toolbar.alreadyLatest'))
+    if (!meta) message = t('toolbar.alreadyLatest')
   } catch (e) {
-    await showAlert(`${t('toolbar.updateCheckFailed')}: ${e}`)
+    message = `${t('toolbar.updateCheckFailed')}: ${localizeUpdateError(e, t)}`
   } finally {
     updateChecking.value = false
   }
+  if (message) await showAlert(message)
 }
 
 async function openProject() {
@@ -174,8 +193,8 @@ const hasConnection = () => selectedConnectionId.value !== null
     </div>
 
     <div class="toolbar-spacer"></div>
-    <button class="toolbar-btn" :disabled="updateChecking" @click="manualCheckUpdate">
-      {{ updateChecking ? t('toolbar.checkingUpdate') : t('toolbar.checkUpdate') }}
+    <button class="toolbar-btn" :disabled="updateBusy" @click="manualCheckUpdate">
+      <span aria-live="polite">{{ updateButtonLabel }}</span>
     </button>
     <LangToggle />
     <VersionBadge />
diff --git a/shared-frontend/src/composables/useUpdateProgress.ts b/shared-frontend/src/composables/useUpdateProgress.ts
new file mode 100644
index 0000000..aa0fbcd
--- /dev/null
+++ b/shared-frontend/src/composables/useUpdateProgress.ts
@@ -0,0 +1,57 @@
+import { computed, onBeforeUnmount, onMounted, ref } from 'vue'
+import { listen, type UnlistenFn } from '@tauri-apps/api/event'
+
+export type UpdateProgressStage = 'idle' | 'checking' | 'downloading' | 'verifying' | 'ready'
+
+export interface UpdateProgress {
+  stage: UpdateProgressStage
+  downloaded: number
+  total: number | null
+  percent: number | null
+}
+
+type Translate = (key: string, params?: Record<string, string | number>) => string
+
+export function updateProgressLabel(progress: UpdateProgress, t: Translate): string {
+  if (progress.stage === 'downloading') {
+    return progress.percent === null
+      ? t('toolbar.downloadingUpdate')
+      : t('toolbar.downloadingUpdatePercent', { percent: progress.percent })
+  }
+  if (progress.stage === 'verifying') return t('toolbar.verifyingUpdate')
+  return t('toolbar.checkingUpdate')
+}
+
+export function localizeUpdateError(error: unknown, t: Translate): string {
+  const message = String(error)
+  if (message.includes('UPDATE_CHECK_TIMEOUT')) return t('toolbar.updateCheckTimeout')
+  if (message.includes('UPDATE_DOWNLOAD_TIMEOUT')) return t('toolbar.updateDownloadTimeout')
+  return message
+}
+
+export function useUpdateProgress(t: Translate) {
+  const progress = ref<UpdateProgress | null>(null)
+  let unlisten: UnlistenFn | null = null
+  let disposed = false
+
+  onMounted(async () => {
+    const stop = await listen<UpdateProgress>('update-progress', (event) => {
+      const next = event.payload
+      progress.value = next.stage === 'idle' || next.stage === 'ready' ? null : next
+    })
+    if (disposed) stop()
+    else unlisten = stop
+  })
+
+  onBeforeUnmount(() => {
+    disposed = true
+    unlisten?.()
+  })
+
+  const active = computed(() => progress.value !== null)
+  const label = computed(() =>
+    progress.value ? updateProgressLabel(progress.value, t) : t('toolbar.checkUpdate'),
+  )
+
+  return { progress, active, label }
+}
diff --git a/shared-frontend/src/i18n/locales/en-US.ts b/shared-frontend/src/i18n/locales/en-US.ts
index 2a325ca..fefb749 100644
--- a/shared-frontend/src/i18n/locales/en-US.ts
+++ b/shared-frontend/src/i18n/locales/en-US.ts
@@ -46,8 +46,13 @@ const messages: Messages = {
     appTitleSlave: 'ModbusSlave',
     checkUpdate: 'Check for Updates',
     checkingUpdate: 'Checking…',
+    downloadingUpdate: 'Downloading…',
+    downloadingUpdatePercent: 'Downloading {percent}%',
+    verifyingUpdate: 'Verifying…',
     alreadyLatest: 'You are on the latest version',
     updateCheckFailed: 'Update check failed',
+    updateCheckTimeout: 'The update server did not respond within 30 seconds. Check your network and try again.',
+    updateDownloadTimeout: 'The update download exceeded 5 minutes. Check your network and try again.',
     openProjectTitle: 'Open Project',
     saveProjectTitle: 'Save Project',
     saveAsTitle: 'Save File As',
diff --git a/shared-frontend/src/i18n/locales/zh-CN.ts b/shared-frontend/src/i18n/locales/zh-CN.ts
index 1e0b236..796fcba 100644
--- a/shared-frontend/src/i18n/locales/zh-CN.ts
+++ b/shared-frontend/src/i18n/locales/zh-CN.ts
@@ -44,8 +44,13 @@ const messages = {
     appTitleSlave: 'ModbusSlave',
     checkUpdate: '检查更新',
     checkingUpdate: '检查中…',
+    downloadingUpdate: '正在下载…',
+    downloadingUpdatePercent: '下载中 {percent}%',
+    verifyingUpdate: '正在校验…',
     alreadyLatest: '已是最新版本',
     updateCheckFailed: '更新检查失败',
+    updateCheckTimeout: '更新服务器 30 秒内未响应，请检查网络后重试',
+    updateDownloadTimeout: '更新包下载超过 5 分钟，请检查网络后重试',
     openProjectTitle: '打开项目',
     saveProjectTitle: '保存项目',
     saveAsTitle: '文件另存为',
diff --git a/shared-frontend/src/index.ts b/shared-frontend/src/index.ts
index 6158ba3..e072cdc 100644
--- a/shared-frontend/src/index.ts
+++ b/shared-frontend/src/index.ts
@@ -39,6 +39,17 @@ export type { DirectionFilter, FcFilter } from './composables/useLogFilter'
 export { useErrorHandler } from './composables/useErrorHandler'
 export type { Toast } from './composables/useErrorHandler'
 
+// Update progress
+export {
+  localizeUpdateError,
+  updateProgressLabel,
+  useUpdateProgress,
+} from './composables/useUpdateProgress'
+export type {
+  UpdateProgress,
+  UpdateProgressStage,
+} from './composables/useUpdateProgress'
+
 // Components
 export { default as AppDialog } from './components/AppDialog.vue'
 export { default as LangToggle } from './components/LangToggle.vue'
diff --git a/shared-frontend/tests/useUpdateProgress.spec.ts b/shared-frontend/tests/useUpdateProgress.spec.ts
new file mode 100644
index 0000000..571958d
--- /dev/null
+++ b/shared-frontend/tests/useUpdateProgress.spec.ts
@@ -0,0 +1,44 @@
+import { describe, expect, it } from 'vitest'
+import {
+  localizeUpdateError,
+  updateProgressLabel,
+  type UpdateProgress,
+} from '../src/composables/useUpdateProgress'
+
+const t = (key: string, params?: Record<string, string | number>) =>
+  params ? `${key}:${JSON.stringify(params)}` : key
+
+function progress(overrides: Partial<UpdateProgress>): UpdateProgress {
+  return {
+    stage: 'checking',
+    downloaded: 0,
+    total: null,
+    percent: null,
+    ...overrides,
+  }
+}
+
+describe('updateProgressLabel', () => {
+  it('shows a numeric download percentage when content length is known', () => {
+    expect(updateProgressLabel(progress({ stage: 'downloading', percent: 42 }), t))
+      .toBe('toolbar.downloadingUpdatePercent:{"percent":42}')
+  })
+
+  it('uses stage labels when percentage is unavailable', () => {
+    expect(updateProgressLabel(progress({ stage: 'downloading' }), t))
+      .toBe('toolbar.downloadingUpdate')
+    expect(updateProgressLabel(progress({ stage: 'verifying' }), t))
+      .toBe('toolbar.verifyingUpdate')
+  })
+})
+
+describe('localizeUpdateError', () => {
+  it('maps stable timeout codes to translated messages', () => {
+    expect(localizeUpdateError('UPDATE_CHECK_TIMEOUT', t)).toBe('toolbar.updateCheckTimeout')
+    expect(localizeUpdateError('UPDATE_DOWNLOAD_TIMEOUT', t)).toBe('toolbar.updateDownloadTimeout')
+  })
+
+  it('preserves other updater errors', () => {
+    expect(localizeUpdateError('signature mismatch', t)).toBe('signature mismatch')
+  })
+})