diff --git a/check_comment_ascii.py b/check_comment_ascii.py
index 98bc9c2e3..57d188b6c 100644
--- a/check_comment_ascii.py
+++ b/check_comment_ascii.py
@@ -1,4 +1,15 @@
 #!/usr/bin/env python3
+
+"""
+Check whether given python files contain non-ASCII comments.
+
+How to check the whole git repo:
+
+```
+$ git ls-files -z -- '*.py' | xargs -0 python3 check_comment_ascii.py
+```
+"""
+
 import sys
 import tokenize
 import ast