diff --git a/ui/desktop/src/components/McpApps/McpAppRenderer.tsx b/ui/desktop/src/components/McpApps/McpAppRenderer.tsx
index e3df201c114d..c78e2b94a95b 100644
--- a/ui/desktop/src/components/McpApps/McpAppRenderer.tsx
+++ b/ui/desktop/src/components/McpApps/McpAppRenderer.tsx
@@ -128,12 +128,22 @@ export default function McpAppRenderer({
           if (!append) {
             throw new Error('Message handler not available in this context');
           }
-          append(content.text);
+
+          if (!Array.isArray(content)) {
+            throw new Error('Invalid message format: content must be an array of ContentBlock');
+          }
+
+          // Extract first text block from content, ignoring other block types
+          const textContent = content.find((block) => block.type === 'text');
+          if (!textContent) {
+            throw new Error('Invalid message format: content must contain a text block');
+          }
+
+          // MCP Apps can send other content block types, but we only append text blocks for now
+
+          append(textContent.text);
           window.dispatchEvent(new CustomEvent('scroll-chat-to-bottom'));
-          return {
-            status: 'success',
-            message: 'Message appended successfully',
-          } satisfies McpMethodResponse['ui/message'];
+          return {} satisfies McpMethodResponse['ui/message'];
         }
 
         case 'tools/call': {
diff --git a/ui/desktop/src/components/McpApps/types.ts b/ui/desktop/src/components/McpApps/types.ts
index 43ce6ecade11..c24c7ae80f85 100644
--- a/ui/desktop/src/components/McpApps/types.ts
+++ b/ui/desktop/src/components/McpApps/types.ts
@@ -1,8 +1,16 @@
 export type { CspMetadata, CallToolResponse as ToolResult } from '../../api/types.gen';
 
+export type ContentBlock =
+  | { type: 'text'; text: string }
+  | { type: 'image'; data: string; mimeType: string }
+  | {
+      type: 'resource';
+      resource: { uri: string; mimeType?: string; text?: string; blob?: string };
+    };
+
 export type McpMethodParams = {
   'ui/open-link': { url: string };
-  'ui/message': { content: { type: string; text: string } };
+  'ui/message': { role: 'user'; content: ContentBlock[] };
   'tools/call': { name: string; arguments?: Record<string, unknown> };
   'resources/read': { uri: string };
   'notifications/message': { level?: string; logger?: string; data: unknown };
@@ -11,7 +19,7 @@ export type McpMethodParams = {
 
 export type McpMethodResponse = {
   'ui/open-link': { status: string; message: string };
-  'ui/message': { status: string; message: string };
+  'ui/message': Record<string, never>;
   'tools/call': {
     content: unknown[];
     isError: boolean;