diff --git a/server/src/matrix/bot.rs b/server/src/matrix/bot.rs
index f335b0f..f87e005 100644
--- a/server/src/matrix/bot.rs
+++ b/server/src/matrix/bot.rs
@@ -167,6 +167,18 @@ pub struct BotContext {
     pub bot_name: String,
 }
 
+// ---------------------------------------------------------------------------
+// Startup announcement
+// ---------------------------------------------------------------------------
+
+/// Format the startup greeting the bot sends to each room when it comes online.
+///
+/// Uses the bot's configured display name so the message reads naturally
+/// (e.g. "Timmy is online.").
+pub fn format_startup_announcement(bot_name: &str) -> String {
+    format!("{bot_name} is online.")
+}
+
 // ---------------------------------------------------------------------------
 // Bot entry point
 // ---------------------------------------------------------------------------
@@ -305,10 +317,11 @@ pub async fn run_bot(
         target_room_ids
     );
 
-    // Clone values needed by the notification listener before they are moved
-    // into BotContext.
+    // Clone values needed by the notification listener and startup announcement
+    // before they are moved into BotContext.
     let notif_room_ids = target_room_ids.clone();
     let notif_project_root = project_root.clone();
+    let announce_room_ids = target_room_ids.clone();
 
     let persisted = load_history(&project_root);
     slog!(
@@ -320,6 +333,7 @@ pub async fn run_bot(
         .display_name
         .clone()
         .unwrap_or_else(|| "Assistant".to_string());
+    let announce_bot_name = bot_name.clone();
 
     let ctx = BotContext {
         bot_user_id,
@@ -351,6 +365,23 @@ pub async fn run_bot(
         notif_project_root,
     );
 
+    // Send a startup announcement to each configured room so users know the
+    // bot is online.  This runs once per process start — the sync loop handles
+    // reconnects internally so this code is never reached again on a network
+    // blip or sync resumption.
+    let announce_msg = format_startup_announcement(&announce_bot_name);
+    slog!("[matrix-bot] Sending startup announcement: {announce_msg}");
+    for room_id in &announce_room_ids {
+        if let Some(room) = client.get_room(room_id) {
+            let content = RoomMessageEventContent::text_plain(announce_msg.clone());
+            if let Err(e) = room.send(content).await {
+                slog!("[matrix-bot] Failed to send startup announcement to {room_id}: {e}");
+            }
+        } else {
+            slog!("[matrix-bot] Room {room_id} not found in client state, skipping announcement");
+        }
+    }
+
     slog!("[matrix-bot] Starting Matrix sync loop");
 
     // This blocks until the connection is terminated or an error occurs.
@@ -1663,6 +1694,19 @@ mod tests {
         assert!(is_permission_approval("\tyes\n"));
     }
 
+    // -- format_startup_announcement ----------------------------------------
+
+    #[test]
+    fn startup_announcement_uses_bot_name() {
+        assert_eq!(format_startup_announcement("Timmy"), "Timmy is online.");
+    }
+
+    #[test]
+    fn startup_announcement_uses_configured_display_name_not_hardcoded() {
+        assert_eq!(format_startup_announcement("HAL"), "HAL is online.");
+        assert_eq!(format_startup_announcement("Assistant"), "Assistant is online.");
+    }
+
     // -- bot_name / system prompt -------------------------------------------
 
     #[test]