diff --git a/README.md b/README.md
index 04de368..70b6a25 100644
--- a/README.md
+++ b/README.md
@@ -38,13 +38,24 @@ just secrets-sync          # shell env vars -> ~/.config/secrets/shell.zsh
 just secrets-restore-files # SSH keys, AWS, GCloud, Codex, GitHub CLI
 ```
 
+## dev
+
+```bash
+nix develop
+just check
+just fmt
+```
+
 ## layout
 
 ```
-hosts/darwin/   - macOS nix-darwin config
-hosts/netty/    - NixOS VPS config (disko + hardware)
-modules/        - system-level modules (packages, macos defaults, homebrew)
-home/           - Home Manager modules (shell, editor, tools)
+hosts/darwin/   - macOS host entrypoint
+hosts/netty/    - NixOS VPS entrypoint (disko + hardware)
+modules/        - shared system modules + devshells
+modules/hosts/  - flake-parts host output definitions
+modules/nixpkgs.nix - shared flake context (hosts, args, pkgs helpers)
+home/           - Home Manager modules
+lib/hosts.nix   - host metadata used by the flake
 lib/            - shared package sets and theme system
 config/         - repo-owned config files (nvim, tmux, etc.)
 scripts/        - secret management and utility scripts
diff --git a/flake.lock b/flake.lock
index 7bb5df8..9718ab1 100644
--- a/flake.lock
+++ b/flake.lock
@@ -76,6 +76,24 @@
         "type": "github"
       }
     },
+    "flake-parts": {
+      "inputs": {
+        "nixpkgs-lib": "nixpkgs-lib"
+      },
+      "locked": {
+        "lastModified": 1772408722,
+        "narHash": "sha256-rHuJtdcOjK7rAHpHphUb1iCvgkU3GpfvicLMwwnfMT0=",
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "rev": "f20dc5d9b8027381c474144ecabc9034d6a839a3",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "type": "github"
+      }
+    },
     "flake-utils": {
       "inputs": {
         "systems": "systems"
@@ -226,6 +244,21 @@
         "type": "github"
       }
     },
+    "nixpkgs-lib": {
+      "locked": {
+        "lastModified": 1772328832,
+        "narHash": "sha256-e+/T/pmEkLP6BHhYjx6GmwP5ivonQQn0bJdH9YrRB+Q=",
+        "owner": "nix-community",
+        "repo": "nixpkgs.lib",
+        "rev": "c185c7a5e5dd8f9add5b2f8ebeff00888b070742",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "nixpkgs.lib",
+        "type": "github"
+      }
+    },
     "nixpkgs_2": {
       "locked": {
         "lastModified": 1767640445,
@@ -265,6 +298,7 @@
         "agentcomputer-cli": "agentcomputer-cli",
         "claudeCode": "claudeCode",
         "disko": "disko",
+        "flake-parts": "flake-parts",
         "googleworkspace-cli": "googleworkspace-cli",
         "home-manager": "home-manager",
         "nix-darwin": "nix-darwin",
diff --git a/flake.nix b/flake.nix
index 557a243..5b340ef 100644
--- a/flake.nix
+++ b/flake.nix
@@ -3,6 +3,7 @@
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    flake-parts.url = "github:hercules-ci/flake-parts";
 
     nix-darwin = {
       url = "github:nix-darwin/nix-darwin/master";
@@ -24,7 +25,6 @@
       inputs.nixpkgs.follows = "nixpkgs";
     };
 
-
     agentcomputer-cli = {
       url = "path:/Users/rathi/Documents/GitHub/companion/agentcomputer/apps/cli";
       inputs.nixpkgs.follows = "nixpkgs";
@@ -44,96 +44,14 @@
     };
   };
 
-  outputs = inputs @ {
-    self,
-    nixpkgs,
-    nix-darwin,
-    home-manager,
-    claudeCode,
-    nix-homebrew,
-    ...
-  }: let
-    darwinSystem = "aarch64-darwin";
-    linuxSystem = "x86_64-linux";
-    username = "rathi";
-    darwinConfigName = "darwin";
-    darwinMachineHostname = "hari-macbook-pro";
-    linuxConfigName = "netty";
-    linuxHostname = "netty";
-    darwinPkgs = import nixpkgs {system = darwinSystem;};
-    linuxPkgs = import nixpkgs {
-      system = linuxSystem;
-      config.allowUnfree = true;
-    };
-  in {
-    formatter.${darwinSystem} = darwinPkgs.alejandra;
-    formatter.${linuxSystem} = linuxPkgs.alejandra;
-
-    darwinConfigurations.${darwinConfigName} = nix-darwin.lib.darwinSystem {
-      system = darwinSystem;
-      specialArgs = {
-        inherit inputs self username;
-        hostname = darwinMachineHostname;
-      };
-      modules = [
-        ./hosts/${darwinConfigName}
-        home-manager.darwinModules.home-manager
-        nix-homebrew.darwinModules.nix-homebrew
-        {
-          users.users.${username}.home = "/Users/${username}";
-
-          home-manager.useGlobalPkgs = true;
-          home-manager.useUserPackages = true;
-          home-manager.extraSpecialArgs = {
-            inherit inputs self username;
-            hostname = darwinMachineHostname;
-          };
-          home-manager.backupFileExtension = "hm-bak";
-          home-manager.users.${username} = import ./home;
-
-          nix-homebrew = {
-            enable = true;
-            enableRosetta = true;
-            user = username;
-            autoMigrate = true;
-          };
-        }
+  outputs =
+    inputs@{ flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      imports = [
+        ./modules/nixpkgs.nix
+        ./modules/devshells.nix
+        ./modules/hosts/darwin.nix
+        ./modules/hosts/netty.nix
       ];
     };
-
-    nixosConfigurations.${linuxConfigName} = nixpkgs.lib.nixosSystem {
-      system = linuxSystem;
-      specialArgs = {
-        inherit inputs self username;
-        hostname = linuxHostname;
-      };
-      modules = [
-        inputs.disko.nixosModules.disko
-        ./hosts/${linuxConfigName}/configuration.nix
-        home-manager.nixosModules.home-manager
-        {
-          home-manager.useGlobalPkgs = true;
-          home-manager.useUserPackages = true;
-          home-manager.extraSpecialArgs = {
-            inherit inputs self username;
-            hostname = linuxHostname;
-          };
-          home-manager.backupFileExtension = "hm-bak";
-          home-manager.users.${username} = import ./home/netty.nix;
-        }
-      ];
-    };
-
-    # Standalone Home Manager config (fallback for non-NixOS Linux)
-    homeConfigurations.${linuxConfigName} = home-manager.lib.homeManagerConfiguration {
-      pkgs = linuxPkgs;
-      extraSpecialArgs = {
-        inherit inputs self username;
-        hostname = linuxConfigName;
-      };
-      modules = [
-        ./hosts/${linuxConfigName}
-      ];
-    };
-  };
 }
diff --git a/home/git.nix b/home/git.nix
index 4d68d8f..7eda60b 100644
--- a/home/git.nix
+++ b/home/git.nix
@@ -2,6 +2,7 @@
   programs.git = {
     enable = true;
     lfs.enable = true;
+    signing.format = "openpgp";
 
     settings = {
       user = {
diff --git a/hosts/netty/configuration.nix b/hosts/netty/configuration.nix
index 0316d87..9fcbe92 100644
--- a/hosts/netty/configuration.nix
+++ b/hosts/netty/configuration.nix
@@ -11,6 +11,7 @@ in {
   imports = [
     ./hardware-configuration.nix
     ./disk-config.nix
+    ../../modules/base.nix
   ];
 
   boot.loader.grub = {
@@ -52,35 +53,12 @@ in {
 
   security.sudo.wheelNeedsPassword = false;
 
-  programs.zsh.enable = true;
-  environment.shells = [pkgs.zsh];
+  nix.settings.trusted-users = lib.mkForce [
+    "root"
+    username
+  ];
 
-  environment.variables = {
-    EDITOR = "nvim";
-    VISUAL = "nvim";
-  };
-
-  nix.settings = {
-    auto-optimise-store = true;
-    experimental-features = [
-      "nix-command"
-      "flakes"
-    ];
-    trusted-users = [
-      "root"
-      username
-    ];
-  };
-
-  nix.gc = {
-    automatic = true;
-    dates = "weekly";
-    options = "--delete-older-than 14d";
-  };
-
-  nixpkgs.config.allowUnfree = true;
-
-  environment.systemPackages = packageSets.core ++ packageSets.extras ++ [
+  environment.systemPackages = packageSets.extras ++ [
     pkgs.bubblewrap
     pkgs.pnpm
   ];
diff --git a/justfile b/justfile
index 8a0c150..ee60ce5 100644
--- a/justfile
+++ b/justfile
@@ -17,7 +17,8 @@ switch config='darwin':
   if [[ "{{config}}" == "darwin" ]]; then
     sudo env PATH="$PATH" nix --extra-experimental-features 'nix-command flakes' run github:nix-darwin/nix-darwin/master#darwin-rebuild -- switch --flake path:.#{{config}}
   else
-    nix --extra-experimental-features 'nix-command flakes' run github:nix-community/home-manager -- switch --flake path:.#{{config}} -b hm-bak
+    backup_ext="hm-bak-$(date +%Y%m%d-%H%M%S)"
+    nix --extra-experimental-features 'nix-command flakes' run github:nix-community/home-manager -- switch --flake path:.#{{config}} -b "$backup_ext"
   fi
 
 fmt:
diff --git a/lib/hosts.nix b/lib/hosts.nix
new file mode 100644
index 0000000..2aaef04
--- /dev/null
+++ b/lib/hosts.nix
@@ -0,0 +1,21 @@
+{ username }:
+{
+  darwin = {
+    name = "darwin";
+    kind = "darwin";
+    system = "aarch64-darwin";
+    hostname = "hari-macbook-pro";
+    homeModule = ../home;
+    homeDirectory = "/Users/${username}";
+  };
+
+  netty = {
+    name = "netty";
+    kind = "nixos";
+    system = "x86_64-linux";
+    hostname = "netty";
+    homeModule = ../home/netty.nix;
+    standaloneHomeModule = ../hosts/netty;
+    homeDirectory = "/home/${username}";
+  };
+}
diff --git a/modules/base.nix b/modules/base.nix
index 8af1303..8e1ed86 100644
--- a/modules/base.nix
+++ b/modules/base.nix
@@ -10,6 +10,7 @@ in {
   nix.enable = true;
 
   nix.settings = {
+    auto-optimise-store = true;
     experimental-features = [
       "nix-command"
       "flakes"
@@ -18,17 +19,28 @@ in {
       "@admin"
       username
     ];
+    use-xdg-base-directories = true;
   };
 
-  nix.gc = {
-    automatic = true;
-    interval = {
-      Weekday = 7;
-      Hour = 3;
-      Minute = 0;
-    };
-    options = "--delete-older-than 14d";
-  };
+  nix.gc =
+    {
+      automatic = true;
+      options = "--delete-older-than 14d";
+    }
+    // (
+      if pkgs.stdenv.isDarwin then
+        {
+          interval = {
+            Weekday = 7;
+            Hour = 3;
+            Minute = 0;
+          };
+        }
+      else
+        {
+          dates = "weekly";
+        }
+    );
 
   nixpkgs.config.allowUnfree = true;
 
diff --git a/modules/devshells.nix b/modules/devshells.nix
new file mode 100644
index 0000000..925c045
--- /dev/null
+++ b/modules/devshells.nix
@@ -0,0 +1,23 @@
+{ ... }:
+{
+  perSystem =
+    { pkgs, ... }:
+    {
+      formatter = pkgs.nixfmt-tree;
+
+      devShells.default = pkgs.mkShell {
+        packages = with pkgs; [
+          deadnix
+          git
+          just
+          nixfmt-tree
+          nodePackages.prettier
+          pre-commit
+          selene
+          shfmt
+          statix
+          stylua
+        ];
+      };
+    };
+}
diff --git a/modules/hosts/darwin.nix b/modules/hosts/darwin.nix
new file mode 100644
index 0000000..12320eb
--- /dev/null
+++ b/modules/hosts/darwin.nix
@@ -0,0 +1,33 @@
+{
+  hosts,
+  inputs,
+  username,
+  mkSpecialArgs,
+  mkHomeManagerModule,
+  ...
+}:
+let
+  host = hosts.darwin;
+in
+{
+  flake.darwinConfigurations.${host.name} = inputs.nix-darwin.lib.darwinSystem {
+    system = host.system;
+    specialArgs = mkSpecialArgs host;
+    modules = [
+      ../../hosts/${host.name}
+      inputs.home-manager.darwinModules.home-manager
+      inputs.nix-homebrew.darwinModules.nix-homebrew
+      {
+        users.users.${username}.home = host.homeDirectory;
+
+        nix-homebrew = {
+          enable = true;
+          enableRosetta = true;
+          user = username;
+          autoMigrate = true;
+        };
+      }
+      (mkHomeManagerModule host)
+    ];
+  };
+}
diff --git a/modules/hosts/netty.nix b/modules/hosts/netty.nix
new file mode 100644
index 0000000..a5d090e
--- /dev/null
+++ b/modules/hosts/netty.nix
@@ -0,0 +1,33 @@
+{
+  hosts,
+  inputs,
+  mkPkgs,
+  mkSpecialArgs,
+  mkHomeManagerModule,
+  ...
+}:
+let
+  host = hosts.netty;
+in
+{
+  flake = {
+    nixosConfigurations.${host.name} = inputs.nixpkgs.lib.nixosSystem {
+      system = host.system;
+      specialArgs = mkSpecialArgs host;
+      modules = [
+        inputs.disko.nixosModules.disko
+        ../../hosts/${host.name}/configuration.nix
+        inputs.home-manager.nixosModules.home-manager
+        (mkHomeManagerModule host)
+      ];
+    };
+
+    homeConfigurations.${host.name} = inputs.home-manager.lib.homeManagerConfiguration {
+      pkgs = mkPkgs host.system;
+      extraSpecialArgs = mkSpecialArgs host;
+      modules = [
+        host.standaloneHomeModule
+      ];
+    };
+  };
+}
diff --git a/modules/nixpkgs.nix b/modules/nixpkgs.nix
new file mode 100644
index 0000000..cbc9007
--- /dev/null
+++ b/modules/nixpkgs.nix
@@ -0,0 +1,45 @@
+{
+  self,
+  inputs,
+  lib,
+  ...
+}:
+let
+  username = "rathi";
+  hosts = import ../lib/hosts.nix { inherit username; };
+
+  mkPkgs =
+    system:
+    import inputs.nixpkgs {
+      inherit system;
+      config.allowUnfree = true;
+    };
+
+  mkSpecialArgs = host: {
+    inherit inputs self username;
+    hostname = host.hostname;
+  };
+
+  mkHomeManagerModule =
+    host:
+    {
+      home-manager.useGlobalPkgs = true;
+      home-manager.useUserPackages = true;
+      home-manager.extraSpecialArgs = mkSpecialArgs host;
+      home-manager.backupCommand = "bash ${../scripts/home-manager-backup.sh}";
+      home-manager.users.${username} = import host.homeModule;
+    };
+in
+{
+  systems = lib.unique (map (host: host.system) (builtins.attrValues hosts));
+
+  _module.args = {
+    inherit
+      username
+      hosts
+      mkPkgs
+      mkSpecialArgs
+      mkHomeManagerModule
+      ;
+  };
+}
diff --git a/scripts/home-manager-backup.sh b/scripts/home-manager-backup.sh
new file mode 100644
index 0000000..f093f91
--- /dev/null
+++ b/scripts/home-manager-backup.sh
@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if [[ $# -eq 0 ]]; then
+  exit 0
+fi
+
+target_path="${1:?expected target path}"
+base_backup="${target_path}.hm-bak"
+
+if [[ ! -e "$base_backup" ]]; then
+  mv "$target_path" "$base_backup"
+  exit 0
+fi
+
+timestamp="$(date +%Y%m%d-%H%M%S)"
+backup_path="${base_backup}.${timestamp}"
+suffix=0
+
+while [[ -e "$backup_path" ]]; do
+  suffix=$((suffix + 1))
+  backup_path="${base_backup}.${timestamp}.${suffix}"
+done
+
+mv "$target_path" "$backup_path"