Integrate pre-commit.

flake.nix

@@ -9,6 +9,10 @@
     };
     agenix.url = "github:ryantm/agenix";
     simple-nixos-mailserver.url = "gitlab:simple-nixos-mailserver/nixos-mailserver/nixos-25.05";
+    git-hooks = {
+      url = "github:cachix/git-hooks.nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
   };
 
   outputs =
@@ -19,11 +23,12 @@
       nixos-hardware,
       agenix,
       simple-nixos-mailserver,
+      git-hooks,
       ...
     }:
     let
       system = "x86_64-linux";
-      overlayUnstable = final: prev: {
+      overlayUnstable = _final: _prev: {
         unstable = import nixpkgsUnstable {
           inherit system;
           config.allowUnfree = true;
@@ -37,12 +42,9 @@
         {
           environment.systemPackages = [ agenix.packages.${system}.default ];
         }
-        (
-          { config, pkgs, ... }:
-          {
-            nixpkgs.overlays = [ overlayUnstable ];
-          }
-        )
+        {
+          nixpkgs.overlays = [ overlayUnstable ];
+        }
       ];
 
       # Common home-manager modules
@@ -71,7 +73,7 @@
             ++ [ hostPath ];
         };
     in
-    {
+    rec {
       nixosConfigurations = {
         nixbox = mkHost {
           hostPath = ./hosts/nixbox;
@@ -94,5 +96,34 @@
           specialArgs = { inherit inputs; };
         };
       };
+
+      checks.${system} = {
+        pre-commit-check = git-hooks.lib.${system}.run {
+          src = ./.;
+          hooks = {
+            # Check formatting of flake.nix
+            nixfmt-rfc-style = {
+              enable = true;
+              files = "^flake\\.nix$";
+            };
+            # Check for dead code in flake.nix
+            deadnix = {
+              enable = true;
+              files = "^flake\\.nix$";
+            };
+            # Flake-specific checks
+            flake-checker.enable = true;
+          };
+        };
+      };
+
+      devShells.${system}.default =
+        let
+          pkgs = nixpkgs.legacyPackages.${system};
+        in
+        pkgs.mkShell {
+          inherit (checks.${system}.pre-commit-check) shellHook;
+          buildInputs = checks.${system}.pre-commit-check.enabledPackages;
+        };
     };
 }