diff --git a/src/ui/src/builder/BuilderHeaderMoreDropdown.vue b/src/ui/src/builder/BuilderHeaderMoreDropdown.vue
index dcff8cc2b..3f9f35fac 100644
--- a/src/ui/src/builder/BuilderHeaderMoreDropdown.vue
+++ b/src/ui/src/builder/BuilderHeaderMoreDropdown.vue
@@ -23,6 +23,28 @@
 			v-model="importConfirmCheckbox"
 			label="Yes, I want to replace the current agent with the imported file"
 		/>
+		<div
+			v-if="importErrorSummary"
+			class="BuilderHeaderMoreDropdown__importError"
+		>
+			<p class="BuilderHeaderMoreDropdown__importError__header">
+				Failed to import the agent
+			</p>
+
+			<p class="BuilderHeaderMoreDropdown__importError__summary">
+				{{ importErrorSummary }}
+			</p>
+
+			<details
+				v-if="importErrorDetails"
+				class="BuilderHeaderMoreDropdown__importError__details"
+			>
+				<summary>Show details</summary>
+				<pre class="BuilderHeaderMoreDropdown__importError__trace">{{
+					importErrorDetails
+				}}</pre>
+			</details>
+		</div>
 	</WdsModal>
 </template>
 
@@ -60,6 +82,8 @@ const toasts = useToasts();
 const importInProgress = ref(false);
 const importConfirmShown = ref(false);
 const importConfirmCheckbox = ref(false);
+const importErrorSummary = ref("");
+const importErrorDetails = ref("");
 
 const importModalActions = computed<ModalAction[]>(() => [
 	{
@@ -68,6 +92,8 @@ const importModalActions = computed<ModalAction[]>(() => [
 		fn: () => {
 			importConfirmCheckbox.value = false;
 			importConfirmShown.value = false;
+			importErrorSummary.value = "";
+			importErrorDetails.value = "";
 		},
 	},
 	{
@@ -105,6 +131,8 @@ async function importModalConfirm() {
 	if (!file) return;
 
 	importInProgress.value = true;
+	importErrorSummary.value = "";
+	importErrorDetails.value = "";
 
 	try {
 		// Prepare form data
@@ -117,6 +145,9 @@ async function importModalConfirm() {
 			body: formData,
 		});
 		if (!response.ok) {
+			const parsed = await response.json();
+			importErrorSummary.value = parsed?.detail?.summary;
+			importErrorDetails.value = parsed?.detail?.details;
 			throw new Error("Failed to connect to import API");
 		}
 		importConfirmShown.value = false;
@@ -162,4 +193,50 @@ async function onSelect(key: string) {
 .BuilderHeaderMoreDropdown:deep(.SharedMoreDropdown__dropdown) {
 	min-width: 220px;
 }
+
+.BuilderHeaderMoreDropdown__importError {
+	margin-top: 16px;
+	padding: 12px 14px;
+	border-radius: 8px;
+	background: rgba(255, 149, 0, 0.08);
+	border: 1px solid rgba(255, 149, 0, 0.35);
+	grid-column: 2 / 4;
+}
+
+.BuilderHeaderMoreDropdown__importError__header {
+	font-weight: 600;
+	color: var(--wdsColorOrange4);
+	font-size: 14px;
+}
+
+.BuilderHeaderMoreDropdown__importError__summary {
+	margin-top: 6px;
+	font-size: 14px;
+}
+
+.BuilderHeaderMoreDropdown__importError__details {
+	margin-top: 10px;
+}
+
+.BuilderHeaderMoreDropdown__importError__details summary {
+	cursor: pointer;
+	font-size: 12px;
+	user-select: none;
+}
+
+.BuilderHeaderMoreDropdown__importError__details summary:hover {
+	text-decoration: underline;
+}
+
+.BuilderHeaderMoreDropdown__importError__trace {
+	margin-top: 8px;
+	max-height: 220px;
+	overflow: auto;
+	padding: 10px;
+	border-radius: 6px;
+	background: rgba(0, 0, 0, 0.05);
+	font-size: 12px;
+	line-height: 1.4;
+	white-space: pre;
+}
 </style>
diff --git a/src/writer/app_runner.py b/src/writer/app_runner.py
index 5395a70c3..dde662f7c 100644
--- a/src/writer/app_runner.py
+++ b/src/writer/app_runner.py
@@ -1207,6 +1207,9 @@ async def import_zip(self, zip_path: str):
                 if not os.path.isdir(wf_dir_path):
                     raise ValueError(".wf directory not found alongside main.py in the archive.")
 
+                # Parse files to ensure there are no errors
+                wf_project.read_files(main_py_dir)
+
                 # Passed all checks; replace current app contents
 
                 logging.info("Copying app at %s", main_py_dir)
diff --git a/src/writer/serve.py b/src/writer/serve.py
index 5f00838bb..bd0ed7a65 100644
--- a/src/writer/serve.py
+++ b/src/writer/serve.py
@@ -263,9 +263,9 @@ async def export_zip():
     @app.post("/api/import")
     async def import_zip(file: UploadFile = File(...)):
         if serve_mode != "edit":
-            raise HTTPException(status_code=403, detail="Invalid mode.")
+            raise HTTPException(status_code=403, detail={"summary": "Invalid mode. Expected 'edit'"})
         if not file.filename or not file.filename.endswith(".zip"):
-            raise HTTPException(status_code=400, detail="Only .zip files are supported.")
+            raise HTTPException(status_code=400, detail={"summary": "Only .zip files are supported."})
 
         MAX_FILE_SIZE = 200 * 1024 * 1024
 
@@ -278,13 +278,13 @@ async def import_zip(file: UploadFile = File(...)):
                     if size > MAX_FILE_SIZE:
                         tmp.close()
                         os.unlink(tmp.name)
-                        raise HTTPException(status_code=413, detail=f"File too large. Max file size: {MAX_FILE_SIZE}")
+                        raise HTTPException(status_code=413, detail={"summary": f"File too large. Max file size: {MAX_FILE_SIZE}"})
                     tmp.write(chunk)
                 tmp_path = tmp.name
             await app_runner.import_zip(tmp_path)
             os.remove(tmp_path)
-        except ValueError:
-            raise HTTPException(status_code=400, detail="Invalid upload.")
+        except ValueError as e:
+            raise HTTPException(status_code=400, detail={"summary": "Invalid archive contents", "details": traceback.format_exc()}) from e
 
     @app.post("/api/autogen")
     async def autogen(requestBody: AutogenRequestBody, request: Request):