diff --git a/packages/puter-js/src/modules/UI.js b/packages/puter-js/src/modules/UI.js
index 849d4cad..abfd43c2 100644
--- a/packages/puter-js/src/modules/UI.js
+++ b/packages/puter-js/src/modules/UI.js
@@ -14,7 +14,11 @@ class AppConnection extends EventListener {
     // Whether the target app is open
     #isOpen;
 
-    constructor(messageTarget, appInstanceID, targetAppInstanceID) {
+    // Whether the target app uses the Puter SDK, and so accepts messages
+    // (Closing and close events will still function.)
+    #usesSDK;
+
+    constructor(messageTarget, appInstanceID, targetAppInstanceID, usesSDK) {
         super([
             'message', // The target sent us something with postMessage()
             'close',   // The target app was closed
@@ -23,6 +27,7 @@ class AppConnection extends EventListener {
         this.appInstanceID = appInstanceID;
         this.targetAppInstanceID = targetAppInstanceID;
         this.#isOpen = true;
+        this.#usesSDK = usesSDK;
 
         // TODO: Set this.#puterOrigin to the puter origin
 
@@ -54,12 +59,21 @@ class AppConnection extends EventListener {
         });
     }
 
+    // Does the target app use the Puter SDK? If not, certain features will be unavailable.
+    get usesSDK() { return this.#usesSDK; }
+
+    // Send a message to the target app. Requires the target to use the Puter SDK.
     postMessage(message) {
         if (!this.#isOpen) {
             console.warn('Trying to post message on a closed AppConnection');
             return;
         }
 
+        if (!this.#usesSDK) {
+            console.warn('Trying to post message to a non-SDK app');
+            return;
+        }
+
         this.messageTarget.postMessage({
             msg: 'messageToApp',
             appInstanceID: this.appInstanceID,
@@ -155,7 +169,7 @@ class UI extends EventListener {
         }
 
         if (this.parentInstanceID) {
-            this.#parentAppConnection = new AppConnection(this.messageTarget, this.appInstanceID, this.parentInstanceID);
+            this.#parentAppConnection = new AppConnection(this.messageTarget, this.appInstanceID, this.parentInstanceID, true);
         }
 
         // Tell the host environment that this app is using the Puter SDK and is ready to receive messages,
@@ -374,7 +388,7 @@ class UI extends EventListener {
                 }
                 else if (e.data.msg === 'childAppLaunched') {
                     // execute callback with a new AppConnection to the child
-                    const connection = new AppConnection(this.messageTarget, this.appInstanceID, e.data.child_instance_id);
+                    const connection = new AppConnection(this.messageTarget, this.appInstanceID, e.data.child_instance_id, e.data.uses_sdk);
                     this.#callbackFunctions[e.data.original_msg_id](connection);
                 }
                 else{
diff --git a/src/IPC.js b/src/IPC.js
index dbe18eb1..6e9b4cc3 100644
--- a/src/IPC.js
+++ b/src/IPC.js
@@ -90,17 +90,7 @@ window.addEventListener('message', async (event) => {
         $(target_iframe).attr('data-appUsesSDK', 'true');
 
         // If we were waiting to launch this as a child app, report to the parent that it succeeded.
-        const child_launch_callback = window.child_launch_callbacks[event.data.appInstanceID];
-        if (child_launch_callback) {
-            const parent_iframe = iframe_for_app_instance(child_launch_callback.parent_instance_id);
-            // send confirmation to requester window
-            parent_iframe.contentWindow.postMessage({
-                msg: 'childAppLaunched',
-                original_msg_id: child_launch_callback.launch_msg_id,
-                child_instance_id: event.data.appInstanceID,
-            }, '*');
-            delete window.child_launch_callbacks[event.data.appInstanceID];
-        }
+        window.report_app_launched(event.data.appInstanceID, { uses_sdk: true });
 
         // Send any saved broadcasts to the new app
         globalThis.services.get('broadcast').sendSavedBroadcastsTo(event.data.appInstanceID);
diff --git a/src/helpers.js b/src/helpers.js
index 5c0ff66a..1273bb2b 100644
--- a/src/helpers.js
+++ b/src/helpers.js
@@ -3523,3 +3523,19 @@ window.window_for_app_instance = (instance_id) => {
 window.iframe_for_app_instance = (instance_id) => {
     return $(window_for_app_instance(instance_id)).find('.window-app-iframe').get(0);
 };
+
+// Run any callbacks to say that the app has launched
+window.report_app_launched = (instance_id, { uses_sdk = true }) => {
+    const child_launch_callback = window.child_launch_callbacks[instance_id];
+    if (child_launch_callback) {
+        const parent_iframe = iframe_for_app_instance(child_launch_callback.parent_instance_id);
+        // send confirmation to requester window
+        parent_iframe.contentWindow.postMessage({
+            msg: 'childAppLaunched',
+            original_msg_id: child_launch_callback.launch_msg_id,
+            child_instance_id: instance_id,
+            uses_sdk: uses_sdk,
+        }, '*');
+        delete window.child_launch_callbacks[instance_id];
+    }
+}