diff --git a/.forgejo/workflows/build.yaml b/.forgejo/workflows/build.yaml
index 89693ab..ee97846 100644
--- a/.forgejo/workflows/build.yaml
+++ b/.forgejo/workflows/build.yaml
@@ -8,4 +8,4 @@ jobs:
     runs-on: native
     steps:
       - uses: actions/checkout@v4
-      - run: nix flake check --all-systems
+      - run: nix-build -A ci.check
diff --git a/default.nix b/default.nix
new file mode 100644
index 0000000..bb13b3b
--- /dev/null
+++ b/default.nix
@@ -0,0 +1,8 @@
+let
+  nilla = import ./nilla.nix { };
+  getPackage = name: nilla.packages.${name}.result.${builtins.currentSystem};
+in
+{
+  ci.check = getPackage "ci-check";
+  formatter = getPackage "formatter";
+}
diff --git a/hosts/default.nix b/hosts/default.nix
index 3c8b713..843a8d1 100644
--- a/hosts/default.nix
+++ b/hosts/default.nix
@@ -16,7 +16,7 @@ in
     ./youko
   ];
 
-  config.configBuilders =
+  config.systems.builders =
     let
       sharedOptions = {
         _file = ./default.nix;
diff --git a/hosts/hijiri-vm/default.nix b/hosts/hijiri-vm/default.nix
index 5f6d088..94350be 100644
--- a/hosts/hijiri-vm/default.nix
+++ b/hosts/hijiri-vm/default.nix
@@ -1,5 +1,5 @@
 {
-  config.configurations.nixos.hijiri-vm =
+  config.systems.nixos.hijiri-vm.module =
     {
       modulesPath,
       lib,
diff --git a/hosts/hijiri/default.nix b/hosts/hijiri/default.nix
index a0e6857..66defb4 100644
--- a/hosts/hijiri/default.nix
+++ b/hosts/hijiri/default.nix
@@ -1,5 +1,5 @@
 {
-  config.configurations.darwin.hijiri =
+  config.systems.darwin.hijiri.module =
     {
       config,
       pkgs,
diff --git a/hosts/kazuki/default.nix b/hosts/kazuki/default.nix
index 029d7d0..d0fad10 100644
--- a/hosts/kazuki/default.nix
+++ b/hosts/kazuki/default.nix
@@ -1,5 +1,5 @@
 {
-  config.configurations.nixos.kazuki =
+  config.systems.nixos.kazuki.module =
     {
       modulesPath,
       ...
diff --git a/hosts/kogata/default.nix b/hosts/kogata/default.nix
index 3e7c21f..d5ac7cb 100644
--- a/hosts/kogata/default.nix
+++ b/hosts/kogata/default.nix
@@ -1,5 +1,5 @@
 {
-  config.configurations.darwin.kogata =
+  config.systems.darwin.kogata.module =
     { pkgs, ... }:
     {
       nixpkgs.system = "aarch64-darwin";
diff --git a/hosts/ude/default.nix b/hosts/ude/default.nix
index fd3e19b..62ffb2e 100644
--- a/hosts/ude/default.nix
+++ b/hosts/ude/default.nix
@@ -1,5 +1,5 @@
 {
-  config.configurations.nixos.ude =
+  config.systems.nixos.ude.module =
     {
       config,
       modulesPath,
diff --git a/hosts/youko/default.nix b/hosts/youko/default.nix
index b801507..7f39ac5 100644
--- a/hosts/youko/default.nix
+++ b/hosts/youko/default.nix
@@ -1,5 +1,5 @@
 {
-  config.configurations.nixos.youko =
+  config.systems.nixos.youko.module =
     {
       config,
       lib,
diff --git a/modules/nilla/configurations.nix b/modules/nilla/configurations.nix
deleted file mode 100644
index 6f02f7e..0000000
--- a/modules/nilla/configurations.nix
+++ /dev/null
@@ -1,47 +0,0 @@
-{ config, lib }:
-{
-  options = {
-    configBuilders = {
-      nixos = lib.options.create {
-        type = lib.types.function lib.types.raw;
-        default.value = _name: config.inputs.nixpkgs.result.lib.nixosSystem;
-      };
-      darwin = lib.options.create {
-        type = lib.types.function lib.types.raw;
-        default.value = _name: config.inputs.darwin.result.lib.darwinSystem;
-      };
-      home = lib.options.create {
-        type = lib.types.function lib.types.raw;
-        default.value = _name: config.inputs.home-manager.result.lib.homeManagerConfiguration;
-      };
-    };
-
-    configurations = {
-      nixos = lib.options.create {
-        type = lib.types.attrs.lazy lib.types.raw;
-        default.value = { };
-      };
-      darwin = lib.options.create {
-        type = lib.types.attrs.lazy lib.types.raw;
-        default.value = { };
-      };
-      home = lib.options.create {
-        type = lib.types.attrs.lazy lib.types.raw;
-        default.value = { };
-      };
-    };
-
-    nixosConfigurations = lib.options.create {
-      type = lib.types.attrs.lazy lib.types.raw;
-      default.value = builtins.mapAttrs config.configBuilders.nixos config.configurations.nixos;
-    };
-    darwinConfigurations = lib.options.create {
-      type = lib.types.attrs.lazy lib.types.raw;
-      default.value = builtins.mapAttrs config.configBuilders.darwin config.configurations.darwin;
-    };
-    homeConfigurations = lib.options.create {
-      type = lib.types.attrs.lazy lib.types.raw;
-      default.value = builtins.mapAttrs config.configBuilders.home config.configurations.home;
-    };
-  };
-}
diff --git a/modules/nilla/default.nix b/modules/nilla/default.nix
index 71aed0d..0cab965 100644
--- a/modules/nilla/default.nix
+++ b/modules/nilla/default.nix
@@ -2,7 +2,7 @@
   includes = [
     ./builders
     ./services.nix
-    ./configurations.nix
+    ./systems.nix
     ./modules.nix
     ./flake.nix
   ];
diff --git a/modules/nilla/flake.nix b/modules/nilla/flake.nix
index f3fe6f1..0193f2d 100644
--- a/modules/nilla/flake.nix
+++ b/modules/nilla/flake.nix
@@ -18,11 +18,12 @@ in
       nixosModules
       darwinModules
       homeModules
-      nixosConfigurations
-      darwinConfigurations
-      homeConfigurations
       ;
 
+    nixosConfigurations = builtins.mapAttrs (_: system: system.result) config.systems.nixos;
+    darwinConfigurations = builtins.mapAttrs (_: system: system.result) config.systems.darwin;
+    homeConfigurations = builtins.mapAttrs (_: system: system.result) config.systems.home;
+
     devShells = transpose config.shells;
     packages = transpose config.packages;
 
diff --git a/modules/nilla/systems.nix b/modules/nilla/systems.nix
new file mode 100644
index 0000000..63b349a
--- /dev/null
+++ b/modules/nilla/systems.nix
@@ -0,0 +1,52 @@
+{ config, lib }:
+let
+  mkBuilderOption =
+    typ:
+    lib.options.create {
+      type = lib.types.function (lib.types.function lib.types.raw);
+      default.value = _name: _module: throw "Builder for systems.${typ} is not implemented";
+    };
+  inherit (config.systems) builders;
+  mkSystemModule =
+    typ:
+    { config, name }:
+    {
+      options = {
+        name = lib.options.create {
+          type = lib.types.string;
+          default.value = name;
+        };
+        module = lib.options.create {
+          type = lib.types.raw;
+          default.value = { };
+        };
+        builder = lib.options.create {
+          type = lib.types.function (lib.types.function lib.types.raw);
+          default.value = builders.${typ};
+        };
+        result = lib.options.create {
+          type = lib.types.raw;
+          writable = false;
+          default.value = config.builder config.name config.module;
+        };
+      };
+    };
+  mkSystemOption =
+    typ:
+    lib.options.create {
+      type = lib.types.attrs.of (lib.types.submodule (mkSystemModule typ));
+      default.value = { };
+    };
+in
+{
+  options = {
+    systems = {
+      builders.nixos = mkBuilderOption "nixos";
+      builders.darwin = mkBuilderOption "darwin";
+      builders.home = mkBuilderOption "home";
+      nixos = mkSystemOption "nixos";
+      darwin = mkSystemOption "darwin";
+      home = mkSystemOption "home";
+    };
+  };
+}
diff --git a/nilla.nix b/nilla.nix
index bc20103..4379f29 100644
--- a/nilla.nix
+++ b/nilla.nix
@@ -76,6 +76,42 @@
             in
             eval.config.build.wrapper;
         };
+        ci-check =
+          let
+            all-packages = builtins.attrValues (builtins.removeAttrs config.packages [ "ci-check" ]);
+            all-packages' = lib.lists.flatten (map (pkg: builtins.attrValues pkg.result) all-packages);
+
+            nixos-systems = builtins.attrValues config.systems.nixos;
+            nixos-systems' = map (system: system.result.config.system.build.toplevel) nixos-systems;
+
+            darwin-systems = builtins.attrValues config.systems.darwin;
+            darwin-systems' = map (system: system.result.config.system.build.toplevel) darwin-systems;
+
+            all-drvs = all-packages' ++ nixos-systems' ++ darwin-systems';
+            all-drvs' = lib.strings.concatMapSep "\n" builtins.unsafeDiscardStringContext all-drvs;
+          in
+          mkPackage (
+            {
+              lib,
+              stdenvNoCC,
+              system,
+            }:
+            stdenvNoCC.mkDerivation {
+              name = "nilla-eval-check";
+              src = lib.cleanSource ./.;
+              doCheck = true;
+
+              allDerivations = all-drvs';
+              formatter = lib.getExe config.packages.formatter.result.${system};
+
+              passAsFile = [ "allDerivations" ];
+
+              installPhase = ''touch "$out"'';
+              checkPhase = ''
+                "$formatter" --ci
+              '';
+            }
+          );
       };
 
     config.shells.default = {