diff --git a/vibn-frontend/app/[workspace]/project/[projectId]/(home)/preview/page.tsx b/vibn-frontend/app/[workspace]/project/[projectId]/(home)/preview/page.tsx
index 524ed400..657c0053 100644
--- a/vibn-frontend/app/[workspace]/project/[projectId]/(home)/preview/page.tsx
+++ b/vibn-frontend/app/[workspace]/project/[projectId]/(home)/preview/page.tsx
@@ -32,6 +32,8 @@ export default function PreviewTab() {
   const bridge = usePreviewBridge();
   const origin = typeof window !== "undefined" ? window.location.origin : "";
 
+  const [deviceMode, setDeviceMode] = useState<"desktop" | "mobile">("desktop");
+
   // Auto-select first preview on load
   useEffect(() => {
     if (!selectedUrl && options.length > 0) {
@@ -50,8 +52,8 @@ export default function PreviewTab() {
 
   return (
     <div style={canvas}>
-      {options.length > 1 && (
-        <div style={toolbar}>
+      <div style={toolbar}>
+        {options.length > 1 && (
           <select
             value={selectedUrl ?? ""}
             onChange={(e) => setSelectedUrl(e.target.value)}
@@ -64,36 +66,96 @@ export default function PreviewTab() {
               </option>
             ))}
           </select>
-        </div>
-      )}
-      <div style={previewFrame}>
-        {loading && !iframeSrc ? (
-          <div style={loaderWrap}>
-            <Loader2
-              className="animate-spin"
-              style={{ width: 22, height: 22, color: "#9c9590" }}
-            />
-          </div>
-        ) : iframeSrc ? (
-          <iframe
-            key={iframeSrc}
-            src={iframeSrc}
-            title="Preview"
-            ref={(el) => {
-              iframeDomRef.current = el;
-              bridge?.registerPreviewIframe(el, iframeSrc);
-            }}
-            onLoad={() => bridge?.notifyPreviewIframeLoaded()}
-            style={iframeStyle}
-            {...(sandboxIframe(iframeSrc, origin)
-              ? { sandbox: SAME_ORIGIN_SANDBOX }
-              : {})}
-          />
-        ) : (
-          <div style={loaderWrap}>
-            <p style={emptyText}>No preview available</p>
-          </div>
         )}
+        <div
+          style={{
+            display: "flex",
+            gap: 4,
+            background: "rgba(255,255,255,0.85)",
+            padding: 4,
+            borderRadius: 8,
+            border: "1px solid rgba(26,26,26,0.12)",
+          }}
+        >
+          <button
+            onClick={() => setDeviceMode("desktop")}
+            style={{
+              padding: "4px 12px",
+              borderRadius: 6,
+              fontSize: "0.8rem",
+              background:
+                deviceMode === "desktop" ? "rgba(0,0,0,0.06)" : "transparent",
+              color: deviceMode === "desktop" ? "#000" : "#666",
+            }}
+          >
+            Desktop
+          </button>
+          <button
+            onClick={() => setDeviceMode("mobile")}
+            style={{
+              padding: "4px 12px",
+              borderRadius: 6,
+              fontSize: "0.8rem",
+              background:
+                deviceMode === "mobile" ? "rgba(0,0,0,0.06)" : "transparent",
+              color: deviceMode === "mobile" ? "#000" : "#666",
+            }}
+          >
+            Mobile
+          </button>
+        </div>
+      </div>
+
+      <div
+        style={{
+          flex: 1,
+          minHeight: 0,
+          display: "flex",
+          justifyContent: "center",
+          alignItems: "center",
+        }}
+      >
+        <div
+          style={{
+            ...(deviceMode === "desktop" ? desktopFrame : mobileFrame),
+            transition: "all 0.3s ease",
+          }}
+        >
+          {deviceMode === "mobile" && <MobileChrome />}
+
+          {loading && !iframeSrc ? (
+            <div style={loaderWrap}>
+              <Loader2
+                className="animate-spin"
+                style={{ width: 22, height: 22, color: "#9c9590" }}
+              />
+            </div>
+          ) : iframeSrc ? (
+            <iframe
+              key={iframeSrc}
+              src={iframeSrc}
+              title="Preview"
+              ref={(el) => {
+                iframeDomRef.current = el;
+                bridge?.registerPreviewIframe(el, iframeSrc);
+              }}
+              onLoad={() => bridge?.notifyPreviewIframeLoaded()}
+              style={{
+                ...iframeStyle,
+                borderRadius: deviceMode === "mobile" ? 44 : 0,
+              }}
+              {...(sandboxIframe(iframeSrc, origin)
+                ? { sandbox: SAME_ORIGIN_SANDBOX }
+                : {})}
+            />
+          ) : (
+            <div style={loaderWrap}>
+              <p style={emptyText}>No preview available</p>
+            </div>
+          )}
+
+          {deviceMode === "mobile" && <div style={homeIndicator} aria-hidden />}
+        </div>
       </div>
     </div>
   );
@@ -130,9 +192,10 @@ const select: React.CSSProperties = {
   color: "#1a1a1a",
 };
 
-const previewFrame: React.CSSProperties = {
+const desktopFrame: React.CSSProperties = {
   flex: 1,
-  minHeight: 0,
+  width: "100%",
+  height: "100%",
   display: "flex",
   flexDirection: "column",
   borderRadius: 14,
@@ -143,6 +206,121 @@ const previewFrame: React.CSSProperties = {
     "0 1px 2px rgba(26, 26, 26, 0.04), 0 12px 40px rgba(26, 26, 26, 0.07), inset 0 1px 0 rgba(255, 255, 255, 0.85)",
 };
 
+const mobileFrame: React.CSSProperties = {
+  position: "relative",
+  width: 390,
+  height: 844,
+  flexShrink: 0,
+  borderRadius: 56,
+  padding: 12,
+  background: "linear-gradient(160deg, #2a2a2c 0%, #1a1a1c 50%, #0e0e10 100%)",
+  boxShadow:
+    "0 0 0 1px rgba(255,255,255,0.04) inset, 0 0 0 2px #000 inset, 0 28px 60px -12px rgba(0,0,0,0.45), 0 8px 20px -8px rgba(0,0,0,0.35)",
+  display: "flex",
+  flexDirection: "column",
+  overflow: "hidden",
+};
+
+const homeIndicator: React.CSSProperties = {
+  position: "absolute",
+  left: "50%",
+  bottom: 20,
+  transform: "translateX(-50%)",
+  width: 134,
+  height: 5,
+  background: "#1a1916",
+  borderRadius: 999,
+  opacity: 0.85,
+  pointerEvents: "none",
+  zIndex: 10,
+};
+
+function MobileChrome() {
+  return (
+    <>
+      <div
+        style={{
+          position: "absolute",
+          top: 22,
+          left: "50%",
+          transform: "translateX(-50%)",
+          width: 124,
+          height: 36,
+          background: "#000",
+          borderRadius: 999,
+          zIndex: 15,
+        }}
+      />
+      <div
+        style={{
+          position: "absolute",
+          top: 12,
+          left: 12,
+          right: 12,
+          height: 47,
+          padding: "18px 26px 0",
+          display: "flex",
+          alignItems: "flex-start",
+          justifyContent: "space-between",
+          fontSize: 15,
+          fontWeight: 600,
+          letterSpacing: "-0.01em",
+          color: "#1a1916",
+          pointerEvents: "none",
+          zIndex: 10,
+        }}
+      >
+        <span>9:41</span>
+        <span style={{ display: "inline-flex", alignItems: "center", gap: 6 }}>
+          <svg
+            viewBox="0 0 17 11"
+            style={{ width: 17, height: 11, fill: "currentColor" }}
+            aria-hidden
+          >
+            <rect x="0" y="7" width="3" height="4" rx="0.6" />
+            <rect x="4" y="5" width="3" height="6" rx="0.6" />
+            <rect x="8" y="3" width="3" height="8" rx="0.6" />
+            <rect x="12" y="0" width="3" height="11" rx="0.6" />
+          </svg>
+          <svg
+            viewBox="0 0 17 11"
+            style={{ width: 17, height: 11, fill: "currentColor" }}
+            aria-hidden
+          >
+            <path d="M8.5 1.5C5.5 1.5 2.7 2.6 0.5 4.6L2 6.1C3.8 4.5 6.1 3.6 8.5 3.6c2.4 0 4.7 0.9 6.5 2.5l1.5-1.5c-2.2-2-5-3.1-8-3.1zM3.5 7.6L5 9.1c1-0.9 2.2-1.4 3.5-1.4 1.3 0 2.5 0.5 3.5 1.4l1.5-1.5c-1.4-1.3-3.1-2-5-2-1.9 0-3.6 0.7-5 2zM6.5 10.6l2 2 2-2c-0.5-0.5-1.2-0.8-2-0.8s-1.5 0.3-2 0.8z" />
+          </svg>
+          <svg
+            viewBox="0 0 25 11"
+            style={{ width: 25, height: 11, fill: "currentColor" }}
+            aria-hidden
+          >
+            <rect
+              x="0.5"
+              y="0.5"
+              width="21"
+              height="10"
+              rx="2.5"
+              fill="none"
+              stroke="currentColor"
+              strokeOpacity="0.45"
+            />
+            <rect
+              x="22"
+              y="3.5"
+              width="1.5"
+              height="4"
+              rx="0.4"
+              fill="currentColor"
+              fillOpacity="0.45"
+            />
+            <rect x="2" y="2" width="18" height="7" rx="1.4" />
+          </svg>
+        </span>
+      </div>
+    </>
+  );
+}
+
 const iframeStyle: React.CSSProperties = {
   flex: 1,
   width: "100%",
diff --git a/vibn-frontend/app/api/chat/route.ts b/vibn-frontend/app/api/chat/route.ts
index f490c1b1..5d214b93 100644
--- a/vibn-frontend/app/api/chat/route.ts
+++ b/vibn-frontend/app/api/chat/route.ts
@@ -217,6 +217,12 @@ Each project has a persistent \`vibn-dev\` container. Edit files via \`fs_*\` an
 
 **Testing Auth & Protected Routes:** Do NOT attempt to verify signup flows or authenticated routes by making HTTP requests (e.g. \`curl\` or \`http_fetch\`) to the dev server yourself. The app is protected by NextAuth or similar session cookies which you do not have. Just write the code, start the dev server via \`dev_server_start\`, and provide the user the clickable \`previewUrl\` so they can test it themselves in their browser. If you hit a redirect/401, do NOT assume the server is broken and loop on restarting it.
 
+**Design Critique / Visual QA Tool:**
+- \`request_visual_qa { targetPath }\` runs a fast background AI agent to critique a UI file (like \`page.tsx\`, \`layout.tsx\`, or \`.css\`) against a strict 5-dimensional design rubric (Layout, Spacing, Contrast, Hierarchy, Responsiveness).
+- You MUST call this tool whenever your turn involves creating or heavily modifying visual User Interface code before you return the \`previewUrl\` to the user.
+- If the tool returns a failure with actionable issues (e.g., "missing mobile padding" or "using hardcoded colors instead of CSS variables"), you MUST use \`fs_edit\` to fix those specific issues before ending your turn.
+- Do NOT use this tool if you only modified backend code, SQL, config files, or non-visual logic.
+
 **Rules:**
 - Stay under \`/workspace\`. \`fs_*\` enforce this; use \`shell_exec\` deliberately for system paths.
 - Dev container has no route to internal Vibn services (vibn-postgres, etc.) by design.
diff --git a/vibn-frontend/app/api/mcp/route.ts b/vibn-frontend/app/api/mcp/route.ts
index d9060d68..6cade175 100644
--- a/vibn-frontend/app/api/mcp/route.ts
+++ b/vibn-frontend/app/api/mcp/route.ts
@@ -40,6 +40,7 @@ import {
 } from "@/lib/workspace-gcs";
 import { VIBN_GCS_LOCATION } from "@/lib/gcp/storage";
 import { getApplicationRuntimeLogs } from "@/lib/coolify-logs";
+import { callVibnChat } from "@/lib/ai/vibn-chat-model";
 import { execInCoolifyApp } from "@/lib/coolify-exec";
 import { isCoolifySshConfigured, runOnCoolifyHost } from "@/lib/coolify-ssh";
 import {
@@ -230,6 +231,7 @@ export async function GET() {
           "browser.console",
           "browser.navigate",
           "ship",
+          "request_visual_qa",
         ],
       },
     },
@@ -414,6 +416,8 @@ export async function POST(request: Request) {
         return await toolShellExec(principal, params);
       case "fs.read":
         return await toolFsRead(principal, params);
+      case "request_visual_qa":
+        return await toolRequestVisualQA(principal, params);
       case "fs.write":
         return await toolFsWrite(principal, params);
       case "fs.edit":
@@ -4485,6 +4489,80 @@ async function runFsCmd(
   };
 }
 
+async function toolRequestVisualQA(
+  principal: Principal,
+  params: Record<string, any>,
+) {
+  const guard = await pathBGuard();
+  if (guard) return guard;
+  const project = await resolveProjectOr404(principal, params);
+  if (project instanceof NextResponse) return project;
+
+  const targetPath = String(params.targetPath ?? "").trim();
+  if (!targetPath) {
+    return NextResponse.json(
+      { error: 'Param "targetPath" is required' },
+      { status: 400 },
+    );
+  }
+
+  const absPath = normalizeFsPath(targetPath);
+  if (absPath instanceof NextResponse) return absPath;
+
+  const r = await runFsCmd(
+    principal,
+    project,
+    `test -f ${shq(absPath)} && cat ${shq(absPath)}`,
+    10000,
+  );
+
+  if (r.code !== 0) {
+    return NextResponse.json({
+      error: `Could not read file ${targetPath}. Ensure the path is correct and the file exists.`,
+    });
+  }
+
+  const fileContent = r.stdout;
+
+  const prompt = `You are a strict, world-class Senior Design QA Engineer.
+Your job is to evaluate the provided UI code against a strict 5-dimensional rubric and catch "AI slop" before the user sees it.
+If the code is flawless and follows the design system perfectly, say "PASS".
+If it fails ANY criteria, list the exact issues and how to fix them. DO NOT rewrite the whole file, just give actionable critique.
+
+## The Rubric (5 Dimensions)
+1. Layout & Composition: Are there overlapping text elements? Is the grid broken on mobile? Do containers overflow unexpectedly?
+2. Spacing & Padding: Is there enough breathing room? Are paddings consistent? (e.g., tight items should have 4-8px gap, sections should have 24-48px).
+3. Contrast & Color: Are hardcoded hex colors (e.g. #FF0000) used instead of Design System CSS variables (e.g. var(--accent), var(--fg))? ALL colors MUST use CSS variables if a design system is active.
+4. Hierarchy: Is the primary action obvious? Is secondary text properly muted?
+5. Responsiveness: Does the UI stack gracefully on mobile (max-width 760px)? Are \`flex-col\` or \`grid-cols-1\` applied at the right breakpoints?
+
+## The Code
+\`\`\`
+${fileContent.slice(0, 15000)}
+\`\`\`
+
+Evaluate the code. Reply with "PASS" or a concise bulleted list of fixes.`;
+
+  try {
+    const aiResponse = await callVibnChat({
+      systemPrompt: prompt,
+      messages: [{ role: "user", content: "Perform the Visual QA critique." }],
+      temperature: 0.1,
+    });
+
+    return NextResponse.json({
+      result: {
+        critique: aiResponse.text || "No feedback generated.",
+        note: "If this returned issues, you MUST fix them using fs.edit before declaring your turn complete.",
+      },
+    });
+  } catch (err: any) {
+    return NextResponse.json({
+      error: `QA Agent failed: ${err.message}`,
+    });
+  }
+}
+
 async function toolFsRead(principal: Principal, params: Record<string, any>) {
   const guard = await pathBGuard();
   if (guard) return guard;
diff --git a/vibn-frontend/lib/ai/vibn-tools.ts b/vibn-frontend/lib/ai/vibn-tools.ts
index 9b0da265..f015cb68 100644
--- a/vibn-frontend/lib/ai/vibn-tools.ts
+++ b/vibn-frontend/lib/ai/vibn-tools.ts
@@ -1449,6 +1449,23 @@ After this returns, ALWAYS call apps_deploy { uuid } to regenerate the live Trae
     },
   },
 
+  {
+    name: "request_visual_qa",
+    description:
+      "Runs a fast background AI agent to critique a UI file (like page.tsx or .css) against a strict 5-dimensional design rubric. Use this before finishing any turn that involves visual changes.",
+    parameters: {
+      type: "OBJECT",
+      properties: {
+        targetPath: {
+          type: "STRING",
+          description:
+            "The path of the file to critique, e.g. apps/web/app/page.tsx",
+        },
+      },
+      required: ["targetPath"],
+    },
+  },
+
   // ── Path B: ship to production ─────────────────────────────────────────────
 
   {