diff --git a/book/_toc.yml b/book/_toc.yml
index dfad3fa..d98f808 100644
--- a/book/_toc.yml
+++ b/book/_toc.yml
@@ -62,6 +62,7 @@ parts:
           - file: features/jupyterlite/including-jupyterlite
 
   - caption: Tools
+    chapters:
     - file: tools/figmaker
     - file: helper_code/intro.md
       sections: