diff --git a/.envrc b/.envrc
new file mode 100644
index 0000000..15c7329
--- /dev/null
+++ b/.envrc
@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+if has nix; then
+  use flake
+fi
diff --git a/.forgejo/actionlint.yaml b/.forgejo/actionlint.yaml
new file mode 100644
index 0000000..8e09575
--- /dev/null
+++ b/.forgejo/actionlint.yaml
@@ -0,0 +1,6 @@
+# Configuration related to self-hosted runner.
+self-hosted-runner:
+  # Labels of self-hosted runner in array of strings.
+  labels:
+    - nixos-latest
+    - nixos-24.11
diff --git a/flake.lock b/flake.lock
index 480733a..9127c6f 100644
--- a/flake.lock
+++ b/flake.lock
@@ -54,7 +54,9 @@
       "inputs": {
         "flake-utils": "flake-utils",
         "nixpkgs": "nixpkgs",
-        "nixpkgs-unstable": "nixpkgs-unstable"
+        "nixpkgs-unstable": "nixpkgs-unstable",
+        "systems": "systems_2",
+        "treefmt-nix": "treefmt-nix"
       }
     },
     "systems": {
@@ -71,6 +73,40 @@
         "repo": "default",
         "type": "github"
       }
+    },
+    "systems_2": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "id": "systems",
+        "type": "indirect"
+      }
+    },
+    "treefmt-nix": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1747912973,
+        "narHash": "sha256-XgxghfND8TDypxsMTPU2GQdtBEsHTEc3qWE6RVEk8O0=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "020cb423808365fa3f10ff4cb8c0a25df35065a3",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
     }
   },
   "root": "root",
diff --git a/flake.nix b/flake.nix
index d42b781..e46e562 100644
--- a/flake.nix
+++ b/flake.nix
@@ -5,14 +5,19 @@
     nixpkgs.url = "github:nixos/nixpkgs/nixos-24.11";
     nixpkgs-unstable.url = "github:nixos/nixpkgs/nixos-unstable";
     flake-utils.url = "github:numtide/flake-utils";
+    # Treefmt for formatting
+    treefmt-nix.url = "github:numtide/treefmt-nix";
+    treefmt-nix.inputs.nixpkgs.follows = "nixpkgs";
   };
 
   outputs =
     {
-      self,
       nixpkgs,
       nixpkgs-unstable,
       flake-utils,
+      treefmt-nix,
+      systems,
+      ...
     }:
     flake-utils.lib.eachDefaultSystem (
       system:
@@ -56,7 +61,7 @@
           in
           pkgs.dockerTools.buildImageWithNixDb {
             name = "git.flyinggecko.org/oci-images/nixos-runner/${name}";
-            tag = tag;
+            inherit tag;
             copyToRoot =
               with pkgs;
               (imagePackages pkgs)
@@ -66,20 +71,20 @@
                   name = "containerPolicy";
                   destination = "/etc/containers/policy.json";
                   text = ''
-                  {
-                      "default": [
-                          {
-                              "type": "insecureAcceptAnything"
-                          }
-                      ],
-                      "transports":
-                          {
-                              "docker-daemon":
-                                  {
-                                      "": [{"type":"insecureAcceptAnything"}]
-                                  }
-                          }
-                  }
+                    {
+                        "default": [
+                            {
+                                "type": "insecureAcceptAnything"
+                            }
+                        ],
+                        "transports":
+                            {
+                                "docker-daemon":
+                                    {
+                                        "": [{"type":"insecureAcceptAnything"}]
+                                    }
+                            }
+                    }
                   '';
                 })
 
@@ -87,14 +92,14 @@
                   name = "containerRegistries";
                   destination = "/etc/containers/registries.conf";
                   text = ''
-                  [registries.block]
-                  registries = []
+                    [registries.block]
+                    registries = []
 
-                  [registries.insecure]
-                  registries = []
+                    [registries.insecure]
+                    registries = []
 
-                  [registries.search]
-                  registries = ["docker.io", "quay.io"]
+                    [registries.search]
+                    registries = ["docker.io", "quay.io"]
                   '';
                 })
 
@@ -230,12 +235,31 @@
               ];
             };
           };
+
+        forEachSystem =
+          f:
+          nixpkgs.lib.genAttrs (import systems) (
+            system:
+            let
+              pkgs = import nixpkgs {
+                inherit system;
+              };
+            in
+            f pkgs
+          );
+        treefmtEval = forEachSystem (pkgs: treefmt-nix.lib.evalModule pkgs ./treefmt.nix);
+        # treefmtWrapper = pkgs: treefmtEval.${pkgs.system}.config.build.wrapper;
       in
       {
         packages = {
           nixos-2411 = containerLambda "nixos" "24.11" nixpkgs;
           nixos-unstable = containerLambda "nixos" "unstable" nixpkgs-unstable;
         };
+
+        # dev shells in project
+        devShells = import ./shell.nix { inherit nixpkgs treefmtEval system; };
+
+        # formatter = forEachSystem (pkgs: treefmtEval.${pkgs.system}.config.build.wrapper);
       }
     );
 }
diff --git a/shell.nix b/shell.nix
new file mode 100644
index 0000000..fe430d9
--- /dev/null
+++ b/shell.nix
@@ -0,0 +1,23 @@
+{
+  nixpkgs,
+  treefmtEval,
+  system,
+  ...
+}:
+let
+  pkgs = nixpkgs.legacyPackages.${system};
+  packages = with pkgs; [
+    podman
+    direnv
+    git
+  ];
+in
+{
+  default = pkgs.mkShell {
+    inherit packages;
+    # nativeBuildInputs = packages;
+    inputsFrom = [
+      treefmtEval.${pkgs.system}.config.build.devShell
+    ];
+  };
+}
diff --git a/treefmt.nix b/treefmt.nix
new file mode 100644
index 0000000..c687d36
--- /dev/null
+++ b/treefmt.nix
@@ -0,0 +1,38 @@
+_: {
+  settings = {
+
+    # General config
+    # allow-missing-formatter = true;
+    on-unmatched = "debug";
+    global.excludes = [
+      # lock files
+      "*.lock"
+    ];
+    formatter.actionlint = {
+      options = [
+        "-config-file"
+        ".forgejo/actionlint.yaml"
+      ];
+      includes = [
+        ".forgejo/workflows/*.yml"
+        ".forgejo/workflows/*.yaml"
+      ];
+    };
+    formatter.yamlfmt.excludes = [
+      ".forgejo/*"
+    ];
+  };
+
+  programs = {
+    # Nix
+    deadnix.enable = true;
+    nixfmt.enable = true;
+    statix.enable = true;
+
+    # Config files
+    yamlfmt.enable = true;
+
+    # ActionLint/forgejo workflows
+    actionlint.enable = true;
+  };
+}