diff --git a/src/Components/App.tsx b/src/Components/App.tsx
index dda87df8..1609e4ef 100644
--- a/src/Components/App.tsx
+++ b/src/Components/App.tsx
@@ -364,6 +364,7 @@ export function App({
           <Viewer
             proxyHandle={proxyHandle}
             setViewerMethods={setViewerMethods}
+            devMode={true}
           />
         </ResizableGrid>
       </>
@@ -410,6 +411,7 @@ export function App({
           <Viewer
             proxyHandle={proxyHandle}
             setViewerMethods={setViewerMethods}
+            devMode={true}
           />
         </ResizableGrid>
       </>
@@ -496,7 +498,11 @@ export function App({
             appEngine={appEngine}
           />
         </React.Suspense>
-        <Viewer proxyHandle={proxyHandle} setViewerMethods={setViewerMethods} />
+        <Viewer
+          proxyHandle={proxyHandle}
+          setViewerMethods={setViewerMethods}
+          devMode={true}
+        />
       </ResizableGrid>
     );
   } else if (appMode === "viewer") {
@@ -519,6 +525,7 @@ export function App({
           <Viewer
             proxyHandle={proxyHandle}
             setViewerMethods={setViewerMethods}
+            devMode={false}
           />
         </div>
       </>
diff --git a/src/Components/Viewer.tsx b/src/Components/Viewer.tsx
index 43fa2cbb..6eb7b629 100644
--- a/src/Components/Viewer.tsx
+++ b/src/Components/Viewer.tsx
@@ -126,9 +126,11 @@ async function resetRAppFrame(
 export function Viewer({
   proxyHandle,
   setViewerMethods,
+  devMode = false,
 }: {
   proxyHandle: ProxyHandle;
   setViewerMethods: React.Dispatch<React.SetStateAction<ViewerMethods>>;
+  devMode?: boolean;
 }) {
   const viewerFrameRef = React.useRef<HTMLIFrameElement>(null);
   const [appRunningState, setAppRunningState] = React.useState<
@@ -268,6 +270,7 @@ export function Viewer({
         await pyodideproxy.callPyAsync({
           fnName: ["_start_app"],
           args: [appName],
+          kwargs: { dev_mode: devMode },
         });
 
         viewerFrameRef.current.src = appInfo.urlPath;
diff --git a/src/hooks/usePyodide.tsx b/src/hooks/usePyodide.tsx
index b80137e6..ed9875af 100644
--- a/src/hooks/usePyodide.tsx
+++ b/src/hooks/usePyodide.tsx
@@ -518,7 +518,8 @@ class ShinyExpressAppModule:
         import shiny.express
         self.app = shiny.express.wrap_express_app(app_path)
 
-async def _start_app(app_name, scope = _shiny_app_registry):
+async def _start_app(app_name, scope = _shiny_app_registry, dev_mode = False):
+    import os
     import sys
     import importlib
     import shiny.express
@@ -537,11 +538,18 @@ async def _start_app(app_name, scope = _shiny_app_registry):
     class ModuleApp:
         app = None
 
+    if dev_mode:
+        # Enable shiny dev mode for error console
+        os.environ["SHINY_DEV_MODE"] = "1"
+
     if shiny.express.is_express_app("app.py", app_dir):
         app_obj = ShinyExpressAppModule(Path(app_dir) / "app.py")
     else:
         app_obj = importlib.import_module(f"{app_name}.app")
 
+    if dev_mode:
+        os.environ.pop("SHINY_DEV_MODE")
+
     scope[app_name] = app_obj
 
     sys.path.remove(app_dir)