diff --git a/qa/zerocash/test-depends-sources-mirror.py b/qa/zerocash/test-depends-sources-mirror.py
index b9f55947..e09c2c23 100755
--- a/qa/zerocash/test-depends-sources-mirror.py
+++ b/qa/zerocash/test-depends-sources-mirror.py
@@ -1,5 +1,13 @@
 #!/usr/bin/env python2
 
+# This script tests that the package mirror at https://z.cash/depends-sources/
+# contains all of the packages required to build this version of Zcash.
+#
+# This script assumes you've just built Zcash, and that as a result of that
+# build, all of the dependency packages have been downloaded into the
+# depends/sources directory (inside the root of this repository). The script
+# checks that all of those files are accessible on the mirror.
+
 import sys
 import os
 import requests