diff --git a/TODO.md b/TODO.md
index 6fb1aee..cc8c116 100644
--- a/TODO.md
+++ b/TODO.md
@@ -13,6 +13,7 @@
 - [ ] literal date matching
 - [x] reading messages from standard input
 - [x] run-time selection of file locking method
+- [ ] add a debug function
 
 ## File formats, encodings and standards