diff --git a/TODO.md b/TODO.md
index 159e1c7cfa6c2164aa20b2e044d5ebb045f5c2c3..099777a25f7022d7177e071fc61c06909e8cf05d 100644
--- a/TODO.md
+++ b/TODO.md
@@ -8,3 +8,5 @@
   copyleft.org/guide/  I set a few of these up by hand already, but perhaps
   there's a way that tex4ht could dump an list of URL redirects automatically
   when it builds the HTML.
+* https://hypothes.is/ might be useful for quickly allowing web readers
+  to add changes.