diff --git a/nixos/modules/tests/exercise-storage.py b/nixos/modules/tests/exercise-storage.py
index 00f3a2cf0a7bb8ceeb21d010a9c022e9e79af5dc..d56232a4919e415c3331b7c8fc105016ca260b46 100755
--- a/nixos/modules/tests/exercise-storage.py
+++ b/nixos/modules/tests/exercise-storage.py
@@ -1,5 +1,11 @@
 #!/usr/bin/env python3
 
+#
+# Create a new file via the web interface of a Tahoe-LAFS client node and then
+# retrieve the contents of that file.  Exit with success if the retrieved
+# contents match what was uploaded originally.
+#
+
 from sys import argv
 from os import urandom
 from subprocess import check_output
@@ -23,11 +29,13 @@ def get_api_root(path):
     with open(path + u"/node.url") as f:
         return f.read().strip()
 
+
 def put(api_root, data):
     response = requests.put(api_root + u"uri", BytesIO(data))
     response.raise_for_status()
     return response.text
 
+
 def get(api_root, cap):
     response = requests.get(api_root + u"uri/" + cap, stream=True)
     response.raise_for_status()
diff --git a/nixos/modules/tests/get-passes.py b/nixos/modules/tests/get-passes.py
index 23e4c69283485170967b6c3bdb0c3f4d33d8721b..ac5cf790fd95d8ce5295879a04d4c19026bf2dba 100755
--- a/nixos/modules/tests/get-passes.py
+++ b/nixos/modules/tests/get-passes.py
@@ -1,5 +1,11 @@
 #!/usr/bin/env python3
 
+#
+# Get a paid voucher and tell the Tahoe-LAFS client node to redeem it for some
+# ZKAPs from an issuer.  Exit with success when the Tahoe-LAFS client node
+# reports that the voucher has been redeemed.
+#
+
 from sys import argv
 from requests import post, get, put
 from json import dumps
diff --git a/nixos/modules/tests/run-client.py b/nixos/modules/tests/run-client.py
index 4b667da71a1cfefbfd59fc14e0547039db9dd893..a246a737232007c95cd364ce5f6566843050a882 100755
--- a/nixos/modules/tests/run-client.py
+++ b/nixos/modules/tests/run-client.py
@@ -1,5 +1,10 @@
 #!/usr/bin/env python3
 
+#
+# Create a PrivateStorage.io-enabled Tahoe-LAFS client node and run it as a
+# daemon.  Exit with success when we think we've started it.
+#
+
 from os import environ
 from sys import argv
 from shutil import which
diff --git a/nixos/modules/tests/run-introducer.py b/nixos/modules/tests/run-introducer.py
index 9f032678aecbad939b4c280a272ab20c0c7c41d9..7a69bdb8240b5dc6b347b960762dd4e2ef0cdde1 100755
--- a/nixos/modules/tests/run-introducer.py
+++ b/nixos/modules/tests/run-introducer.py
@@ -1,5 +1,10 @@
 #!/usr/bin/env python3
 
+#
+# Create a Tahoe-LAFS introducer node and run it as a daemon.  Exit with
+# success when it is accepting introducer client connections.
+#
+
 from sys import argv
 from os import environ, makedirs, rename
 from shutil import which