diff --git a/src/gui/src/IPC.js b/src/gui/src/IPC.js
index 54e1a858d..c9a2fd3be 100644
--- a/src/gui/src/IPC.js
+++ b/src/gui/src/IPC.js
@@ -257,6 +257,20 @@ const ipc_listener = async (event, handled) => {
         }, '*');
     }
     //--------------------------------------------------------
+    // getInstancesOpen
+    //--------------------------------------------------------
+    else if(event.data.msg === 'getInstancesOpen'){
+        // count open windows of this app
+        let instances_open = $('.window-app[data-app_uuid="'+app_uuid+'"]').length;
+
+        // send number of open instances of this app
+        target_iframe.contentWindow.postMessage({
+            original_msg_id: msg_id,
+            msg: 'instancesOpenSucceeded',
+            instancesOpen: instances_open,
+        }, '*');
+    }
+    //--------------------------------------------------------
     // socialShare
     //--------------------------------------------------------
     else if(event.data.msg === 'socialShare' && event.data.url !== undefined){
diff --git a/src/puter-js/src/modules/UI.js b/src/puter-js/src/modules/UI.js
index a32741fdc..d302de154 100644
--- a/src/puter-js/src/modules/UI.js
+++ b/src/puter-js/src/modules/UI.js
@@ -395,6 +395,12 @@ class UI extends EventListener {
                     this.#callbackFunctions[e.data.original_msg_id](appDataItem);
                 }
             }
+            // instancesOpenSucceeded
+            else if(e.data.msg === 'instancesOpenSucceeded'){
+                if(e.data.original_msg_id && this.#callbackFunctions[e.data.original_msg_id]){
+                    this.#callbackFunctions[e.data.original_msg_id](e.data.instancesOpen);
+                }
+            }
             // readAppDataFileSucceeded
             else if(e.data.msg === 'readAppDataFileSucceeded'){
                 let appDataItem = new FSItem(e.data.item);
@@ -657,6 +663,12 @@ class UI extends EventListener {
         })
     }
 
+    instancesOpen = function(callback) {
+        return new Promise((resolve) => {
+            this.#postMessageWithCallback('getInstancesOpen', resolve, {  });
+        })
+    }
+
     socialShare = function(url, message, options, callback) {
         return new Promise((resolve) => {
             this.#postMessageWithCallback('socialShare', resolve, { url, message, options });