diff --git a/web/monitor.py b/web/monitor.py
index 52f33c8..dcfca73 100644
--- a/web/monitor.py
+++ b/web/monitor.py
@@ -542,6 +542,25 @@ def api_screen_text():
         return jsonify({"ok": False, "error": f"输入失败: {e}"}), 503
 
 
+@bp.route("/api/screen/size")
+@perm_required(PERM_DEVICES)
+def api_screen_size():
+    """屏幕原生分辨率（只读，供 MCP 坐标换算：截图是缩放图，操作需原生坐标）。
+
+    返回 {ok, width, height}（如 1080x2400）；离线/不可达 → 503。
+    """
+    serial = request.args.get("serial", "")
+    if not serial:
+        return jsonify({"ok": False, "error": "缺少 serial"}), 400
+    try:
+        d = _screen_get_device(serial)
+        w, h = d.window_size()
+        return jsonify({"ok": True, "width": w, "height": h})
+    except Exception as e:
+        _screen_invalidate(serial)
+        return jsonify({"ok": False, "error": f"获取分辨率失败: {e}"}), 503
+
+
 # ================== API：应用管理（APK 上传/安装）==================
 
 def _current_focus_pkg(serial):