diff --git a/clang/utils/CmpDriver b/clang/utils/CmpDriver
index 2533f547e973..12ce7a3250f6 100755
--- a/clang/utils/CmpDriver
+++ b/clang/utils/CmpDriver
@@ -1,5 +1,10 @@
 #!/usr/bin/env python
 
+"""
+A simple utility that compares tool invocations and exit codes issued by
+compiler drivers that support -### (e.g. gcc and clang).
+"""
+
 import subprocess
 
 def splitArgs(s):