diff --git a/shared/foundryvtt/default.nix b/shared/foundryvtt/default.nix
index 32a58b2a..449da38f 100644
--- a/shared/foundryvtt/default.nix
+++ b/shared/foundryvtt/default.nix
@@ -1,6 +1,18 @@
-# FoundryVTT is licensed software and needs to be downloaded after
-# purchase.
-
+# [FoundryVTT][] is a virtual tabletop to run roleplaying games.  It is licensed
+# software and needs to be downloaded after purchase.  This module doesn't
+# manage the FoundryVTT program files, only operating it.
+#
+# The downloaded FoundryVTT program files must be in
+# `{nixfiles.foundryvtt.dataDir}/bin`.
+#
+# If the `backups` module is enabled, adds a script to backup the data files.
+# This requires briefly stopping the service, so don't schedule backups during
+# game time.
+#
+# If the `erase-your-darlings` module is enabled, stores its data on the
+# persistent volume.
+#
+# [FoundryVTT]: https://foundryvtt.com/
 { config, lib, pkgs, ... }:
 
 with lib;
diff --git a/shared/foundryvtt/options.nix b/shared/foundryvtt/options.nix
index 18901369..9f59e5ea 100644
--- a/shared/foundryvtt/options.nix
+++ b/shared/foundryvtt/options.nix
@@ -4,8 +4,33 @@ with lib;
 
 {
   options.nixfiles.foundryvtt = {
-    enable = mkOption { type = types.bool; default = false; };
-    port = mkOption { type = types.int; default = 46885; };
-    dataDir = mkOption { type = types.str; default = "/var/lib/foundryvtt"; };
+    enable = mkOption {
+      type = types.bool;
+      default = false;
+      description = mdDoc ''
+        Enable the `foundryvtt` service.
+      '';
+    };
+
+    port = mkOption {
+      type = types.int;
+      default = 46885;
+      description = mdDoc ''
+        Port (on 127.0.0.1) to expode the foundryvtt service on.
+      '';
+    };
+
+    dataDir = mkOption {
+      type = types.str;
+      default = "/var/lib/foundryvtt";
+      description = mdDoc ''
+        Directory to store data files in.
+
+        The downloaded FoundryVTT program files must be in `''${dataDir}/bin`.
+
+        If the `erase-your-darlings` module is enabled, this is overridden to be
+        on the persistent volume.
+      '';
+    };
   };
 }