diff --git a/book/_config.yml b/book/_config.yml
index f76acde..b959ce9 100644
--- a/book/_config.yml
+++ b/book/_config.yml
@@ -25,9 +25,11 @@ sphinx:
       launch_buttons:
         thebe: true
     html_show_copyright: false
+    html_last_updated_fmt: '%B %-d %Y'
   extra_extensions:
     - sphinx.ext.imgconverter
     - jupyterbook_patches
+    - sphinx.ext.extlinks
 
 bibtex_bibfiles: 
   - references.bib