diff --git a/flake.nix b/flake.nix
index 557d3a1..98d4faf 100644
--- a/flake.nix
+++ b/flake.nix
@@ -152,6 +152,18 @@
         nixosConfigurationsMinimal
         ;
 
+      # XXX: WIP: only testing
+      d2diag = let
+        inherit
+          (nixpkgs.lib)
+          attrValues
+          concatLines
+          ;
+      in
+        self.pkgs.x86_64-linux.writeText "test.d2" (
+          concatLines (map (x: x.config.d2diag.text) (attrValues self.nixosConfigurations))
+        );
+
       # All nixosSystem instanciations are collected here, so that we can refer
       # to any system via nodes.<name>
       nodes = self.nixosConfigurations // self.guestConfigs;
diff --git a/modules/d2diag.nix b/modules/d2diag.nix
new file mode 100644
index 0000000..50e0a92
--- /dev/null
+++ b/modules/d2diag.nix
@@ -0,0 +1,85 @@
+{
+  config,
+  lib,
+  nodes,
+  ...
+}: let
+  inherit
+    (lib)
+    attrNames
+    concatMap
+    getAttrFromPath
+    mkMerge
+    mkOption
+    optionals
+    types
+    ;
+
+  nodeName = config.node.name;
+in {
+  options.d2diag.text = mkOption {
+    # TODO readonly, _text
+    description = "TODO";
+    type = types.lines;
+  };
+
+  options.d2diag.services = mkOption {
+    description = "TODO";
+    type = types.attrsOf (types.submodule {
+      options = {
+      };
+    });
+  };
+
+  config = {
+    d2diag.text =
+      ''
+        ${nodeName}: ${nodeName} {
+          disks: Disks {
+            shape: sql_table
+            ${lib.concatLines (map (x: "${x}: 8TB") (lib.attrNames config.disko.devices.disk))}
+          }
+          net: Interfaces {
+            shape: sql_table
+            ${lib.concatLines (lib.mapAttrsToList (n: v: ''${n}: ${v.mac}'') (config.repo.secrets.local.networking.interfaces or {lan.mac = "?";}))}
+          }
+      ''
+      + (lib.optionalString (config.guests != {}) ''
+        guests: {
+          ${
+          lib.concatLines (
+            lib.flip lib.mapAttrsToList config.guests (
+              guestName: guestDef:
+                (
+                  if guestDef.backend == "microvm"
+                  then config.microvm.vms.${guestName}.config
+                  else config.containers.${guestName}.nixosConfiguration
+                )
+                .config
+                .d2diag
+                .text
+            )
+          )
+        }
+        }
+
+        ${
+          lib.concatLines (
+            lib.flip lib.mapAttrsToList config.guests (
+              guestName: guestDef: "net.lan -> guests.${(
+                  if guestDef.backend == "microvm"
+                  then config.microvm.vms.${guestName}.config
+                  else config.containers.${guestName}.nixosConfiguration
+                )
+                .config
+                .node
+                .name}.net.lan"
+            )
+          )
+        }
+      '')
+      + ''
+        }
+      '';
+  };
+}
diff --git a/modules/default.nix b/modules/default.nix
index 80860e8..87cda06 100644
--- a/modules/default.nix
+++ b/modules/default.nix
@@ -40,6 +40,8 @@
     ./telegraf.nix
     ./wireguard-proxy.nix
     ./wireguard.nix
+
+    ./d2diag.nix
   ];
 
   nixpkgs.overlays = [