diff --git a/infra/common/options.nix b/infra/common/options.nix
index 2e993b18..a3246fd5 100644
--- a/infra/common/options.nix
+++ b/infra/common/options.nix
@@ -5,31 +5,77 @@ let
 
 in
 {
-  options = {
-    procolixVm = {
-      name = mkOption { };
-      domain = mkOption { default = "procolix.com"; };
+  options.procolixVm = {
+    name = mkOption {
+      description = ''
+        The name of the machine. Most of the time, this will look like `vm02XXX`
+        or `fediYYY`.
+      '';
+    };
 
-      ipv4 = {
-        address = mkOption { };
-        prefixLength = mkOption {
-          default = 24;
-        };
-        gateway = mkOption { default = "185.206.232.1"; };
-      };
+    domain = mkOption {
+      description = ''
+        The domain hosting the machine. Most of the time, this will be either of
+        `procolix.com`, `fediversity.eu` or `abundos.eu`.
+      '';
+      default = "procolix.com";
+    };
 
-      ipv6 = {
-        address = mkOption { };
-        prefixLength = mkOption { default = 64; };
-        gateway = mkOption { default = "2a00:51c0:12:1201::1"; };
-      };
-
-      hostPublicKey = mkOption {
+    ipv4 = {
+      address = mkOption {
         description = ''
-          The host public key of the machine. It is used in particular
-          to filter Age secrets and only keep the relevant ones.
+          The IP address of the machine, version 4. It will be injected as a
+          value in `networking.interfaces.eth0`, but it will also be used to
+          communicate with the machine via NixOps4.
         '';
       };
+
+      prefixLength = mkOption {
+        description = ''
+          The subnet mask of the interface, specified as the number of bits in
+          the prefix.
+        '';
+        default = 24;
+      };
+
+      gateway = mkOption {
+        description = ''
+          The IP address of the default gateway.
+        '';
+        default = "185.206.232.1"; # FIXME: compute default from `address` and `prefixLength`.
+      };
+    };
+
+    ipv6 = {
+      address = mkOption {
+        description = ''
+          The IP address of the machine, version 6. It will be injected as a
+          value in `networking.interfaces.eth0`, but it will also be used to
+          communicate with the machine via NixOps4.
+        '';
+      };
+
+      prefixLength = mkOption {
+        description = ''
+          The subnet mask of the interface, specified as the number of bits in
+          the prefix.
+        '';
+        default = 64;
+      };
+
+      gateway = mkOption {
+        description = ''
+          The IP address of the default gateway.
+        '';
+        default = "2a00:51c0:12:1201::1"; # FIXME: compute default from `address` and `prefixLength`.
+      };
+    };
+
+    hostPublicKey = mkOption {
+      description = ''
+        The host public key of the machine. It is used to filter Age secrets and
+        only keep the relevant ones, and to feed to NixOps4.
+      '';
     };
   };
 }