diff --git a/src/calibre/utils/rapydscript.py b/src/calibre/utils/rapydscript.py
index 06cc1061eb..61c9405d6c 100644
--- a/src/calibre/utils/rapydscript.py
+++ b/src/calibre/utils/rapydscript.py
@@ -215,7 +215,10 @@ def compile_srv():
     base = P('content-server', allow_user_override=False)
     fname = os.path.join(rapydscript_dir, 'srv.pyj')
     with lopen(fname, 'rb') as f:
-        js = compile_fast(f.read(), fname).replace('__RENDER_VERSION__', rv, 1).replace('__MATHJAX_VERSION__', mathjax_version, 1).encode('utf-8')
+        js = compile_fast(f.read(), fname).replace(
+            '__RENDER_VERSION__', rv, 1).replace(
+            '__MATHJAX_VERSION__', mathjax_version, 1).replace(
+            '__CALIBRE_VERSION__', __version__, 1).encode('utf-8')
     with lopen(os.path.join(base, 'index.html'), 'rb') as f:
         html = f.read().replace(b'RESET_STYLES', reset, 1).replace(b'ICONS', icons, 1).replace(b'MAIN_JS', js, 1)
 
diff --git a/src/pyj/read_book/iframe.pyj b/src/pyj/read_book/iframe.pyj
index 71342bfda1..446ef5f0da 100644
--- a/src/pyj/read_book/iframe.pyj
+++ b/src/pyj/read_book/iframe.pyj
@@ -28,10 +28,38 @@ from read_book.touch import create_handlers as create_touch_handlers
 from utils import debounce
 
 FORCE_FLOW_MODE = False
+CALIBRE_VERSION = '__CALIBRE_VERSION__'
+ERS_SUPPORTED_FEATURES = {'dom-manipulation', 'layout-changes', 'touch-events', 'mouse-events', 'keyboard-events', 'spine-scripting'}
+
+
+class EPUBReadingSystem:
+
+    @property
+    def name(self):
+        return 'calibre'
+
+    @property
+    def version(self):
+        return CALIBRE_VERSION
+
+    @property
+    def layoutStyle(self):
+        return 'scrolling' if current_layout_mode() is 'flow' else 'paginated'
+
+    def hasFeature(self, feature, version):
+        return feature in ERS_SUPPORTED_FEATURES
+
+    def __repr__(self):
+        return f'{{name:{self.name}, version:{self.version}, layoutStyle:{self.layoutStyle}}}'
+
+    def __str__(self):
+        return self.__repr__()
+
 
 class IframeBoss:
 
     def __init__(self):
+        window.navigator.epubReadingSystem = EPUBReadingSystem()
         self.ready_sent = False
         self.last_cfi = None
         self.replace_history_on_next_cfi_update = True