diff --git a/.envrc b/.envrc
index 57b77334..e66afc9e 100644
--- a/.envrc
+++ b/.envrc
@@ -1,4 +1,5 @@
+# shellcheck shell=bash
 strict_env
 source ./direnvrc
-watch_file direnvrc *.nix
+watch_file direnvrc ./*.nix
 use flake
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 10791b87..b2c9def0 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -10,17 +10,16 @@ jobs:
   tests:
     strategy:
       matrix:
-        os: [ ubuntu-latest ]
+        os: [ubuntu-latest]
         # FIXME macos garbage currently collect also nix-shell that runs the test
         #os: [ ubuntu-latest, macos-latest ]
-        variants: [ stable, latest, bash4 ]
+        variants: [stable, latest, bash4]
     runs-on: ${{ matrix.os }}
     steps:
-    - uses: actions/checkout@v4
-    - uses: cachix/install-nix-action@V27
-      with:
-        nix_path: nixpkgs=channel:nixpkgs-unstable
-        extra_nix_config: |
-          experimental-features = nix-command flakes
-    - run:
-        "nix run --accept-flake-config .#test-runner-${{ matrix.variants }}"
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@V27
+        with:
+          nix_path: nixpkgs=channel:nixpkgs-unstable
+          extra_nix_config: |
+            experimental-features = nix-command flakes
+      - run: "nix run --accept-flake-config .#test-runner-${{ matrix.variants }}"
diff --git a/.github/workflows/update-flake-lock.yml b/.github/workflows/update-flake-lock.yml
index f26f25fb..29b40884 100644
--- a/.github/workflows/update-flake-lock.yml
+++ b/.github/workflows/update-flake-lock.yml
@@ -24,5 +24,5 @@ jobs:
             ```
             {{ env.GIT_COMMIT_MESSAGE }}
             ```
-          pr-labels: |                  # Labels to be set on the PR
+          pr-labels: | # Labels to be set on the PR
             merge-queue
diff --git a/default.nix b/default.nix
index 5657e52c..5c1beeba 100644
--- a/default.nix
+++ b/default.nix
@@ -1,4 +1,10 @@
-{ resholve, lib, coreutils, direnv, nix }:
+{
+  resholve,
+  lib,
+  coreutils,
+  direnv,
+  nix,
+}:
 
 # resholve does not yet support `finalAttrs` call pattern hence `rec`
 # https://github.com/abathur/resholve/issues/107
@@ -24,7 +30,10 @@ resholve.mkDerivation rec {
     default = {
       scripts = [ "share/${pname}/direnvrc" ];
       interpreter = "none";
-      inputs = [ coreutils nix ];
+      inputs = [
+        coreutils
+        nix
+      ];
       fake = {
         builtin = [
           "PATH_add"
diff --git a/flake.lock b/flake.lock
index 781a82a4..5e42df1c 100644
--- a/flake.lock
+++ b/flake.lock
@@ -22,11 +22,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1720368505,
-        "narHash": "sha256-5r0pInVo5d6Enti0YwUSQK4TebITypB42bWy5su3MrQ=",
+        "lastModified": 1720955038,
+        "narHash": "sha256-GaliJqfFwyYxReFywxAa8orCO+EnDq2NK2F+5aSc8vo=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "ab82a9612aa45284d4adf69ee81871a389669a9e",
+        "rev": "aa247c0c90ecf4ae7a032c54fdc21b91ca274062",
         "type": "github"
       },
       "original": {
@@ -50,11 +50,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1720374026,
-        "narHash": "sha256-ludjqxhR/5lXwJ1H6zHmZqp+4e8dFPHE9FIZ2eBh2G4=",
+        "lastModified": 1720930114,
+        "narHash": "sha256-VZK73b5hG5bSeAn97TTcnPjXUXtV7j/AtS4KN8ggCS0=",
         "owner": "numtide",
         "repo": "treefmt-nix",
-        "rev": "e1d7bd5ec6fc389eb3a90e232c4150338bf6a508",
+        "rev": "b92afa1501ac73f1d745526adc4f89b527595f14",
         "type": "github"
       },
       "original": {
diff --git a/flake.nix b/flake.nix
index b1cdfb48..caa9e052 100644
--- a/flake.nix
+++ b/flake.nix
@@ -2,7 +2,9 @@
   description = "A faster, persistent implementation of `direnv`'s `use_nix`, to replace the built-in one.";
 
   nixConfig.extra-substituters = [ "https://cache.thalheim.io" ];
-  nixConfig.extra-trusted-public-keys = [ "cache.thalheim.io-1:R7msbosLEZKrxk/lKxf9BTjOOH7Ax3H0Qj0/6wiHOgc=" ];
+  nixConfig.extra-trusted-public-keys = [
+    "cache.thalheim.io-1:R7msbosLEZKrxk/lKxf9BTjOOH7Ax3H0Qj0/6wiHOgc="
+  ];
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
@@ -16,9 +18,11 @@
     };
   };
 
-  outputs = inputs @ { flake-parts, ... }:
-    flake-parts.lib.mkFlake { inherit inputs; }
-      ({ lib, ... }: {
+  outputs =
+    inputs@{ flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } (
+      { lib, ... }:
+      {
         imports = [
           ./treefmt.nix
           ./pkgs/bash4/flake-module.nix
@@ -30,37 +34,42 @@
           "x86_64-darwin"
           "aarch64-darwin"
         ];
-        perSystem = { config, pkgs, self', ... }: {
-          packages = {
-            nix-direnv = pkgs.callPackage ./default.nix { };
-            default = config.packages.nix-direnv;
-            test-runner-stable = pkgs.callPackage ./test-runner.nix {
-              nixVersion = "stable";
+        perSystem =
+          {
+            config,
+            pkgs,
+            self',
+            ...
+          }:
+          {
+            packages = {
+              nix-direnv = pkgs.callPackage ./default.nix { };
+              default = config.packages.nix-direnv;
+              test-runner-stable = pkgs.callPackage ./test-runner.nix { nixVersion = "stable"; };
+              test-runner-latest = pkgs.callPackage ./test-runner.nix { nixVersion = "latest"; };
             };
-            test-runner-latest = pkgs.callPackage ./test-runner.nix {
-              nixVersion = "latest";
+
+            devShells.default = pkgs.callPackage ./shell.nix {
+              packages = [
+                config.treefmt.build.wrapper
+                pkgs.shellcheck
+              ];
             };
-          };
 
-          devShells.default = pkgs.callPackage ./shell.nix {
-            packages = [ config.treefmt.build.wrapper pkgs.shellcheck ];
+            checks =
+              let
+                packages = lib.mapAttrs' (n: lib.nameValuePair "package-${n}") self'.packages;
+                devShells = lib.mapAttrs' (n: lib.nameValuePair "devShell-${n}") self'.devShells;
+              in
+              packages // devShells;
           };
-
-          checks =
-            let
-              packages = lib.mapAttrs' (n: lib.nameValuePair "package-${n}") self'.packages;
-              devShells = lib.mapAttrs' (n: lib.nameValuePair "devShell-${n}") self'.devShells;
-            in
-            packages // devShells;
-        };
         flake = {
-          overlays.default = final: _prev: {
-            nix-direnv = final.callPackage ./default.nix { };
-          };
+          overlays.default = final: _prev: { nix-direnv = final.callPackage ./default.nix { }; };
           templates.default = {
             path = ./templates/flake;
             description = "nix flake new -t github:Mic92/nix-direnv .";
           };
         };
-      });
+      }
+    );
 }
diff --git a/pkgs/bash4/default.nix b/pkgs/bash4/default.nix
index a3376e94..7e1ddf30 100644
--- a/pkgs/bash4/default.nix
+++ b/pkgs/bash4/default.nix
@@ -8,8 +8,11 @@ bash.overrideAttrs (_old: {
   };
 
   # generated with update-patch-set.sh from nixpkgs/pkgs/shells/bash
-  patches = import ./bash-4.4-patches.nix (nr: sha256: fetchurl {
-    url = "mirror://gnu/bash/bash-4.4-patches/bash44-${nr}";
-    inherit sha256;
-  });
+  patches = import ./bash-4.4-patches.nix (
+    nr: sha256:
+    fetchurl {
+      url = "mirror://gnu/bash/bash-4.4-patches/bash44-${nr}";
+      inherit sha256;
+    }
+  );
 })
diff --git a/pkgs/bash4/flake-module.nix b/pkgs/bash4/flake-module.nix
index 3d3683ed..be2180ed 100644
--- a/pkgs/bash4/flake-module.nix
+++ b/pkgs/bash4/flake-module.nix
@@ -1,13 +1,14 @@
-{ self, withSystem, ... }: {
-  flake.packages.x86_64-linux = withSystem "x86_64-linux"
-    ({ pkgs, ... }: {
+{ self, withSystem, ... }:
+{
+  flake.packages.x86_64-linux = withSystem "x86_64-linux" (
+    { pkgs, ... }:
+    {
       bash4 = pkgs.callPackage ./. { };
-      direnv-bash4 = pkgs.direnv.override {
-        bash = self.packages.x86_64-linux.bash4;
-      };
+      direnv-bash4 = pkgs.direnv.override { bash = self.packages.x86_64-linux.bash4; };
       test-runner-bash4 = pkgs.callPackage ../../test-runner.nix {
         nixVersion = "stable";
         direnv = self.packages.x86_64-linux.direnv-bash4;
       };
-    });
+    }
+  );
 }
diff --git a/shell.nix b/shell.nix
index d32920a1..da9bc2d2 100644
--- a/shell.nix
+++ b/shell.nix
@@ -1,4 +1,7 @@
-{ pkgs ? import <nixpkgs> { }, packages ? [ ] }:
+{
+  pkgs ? import <nixpkgs> { },
+  packages ? [ ],
+}:
 
 with pkgs;
 mkShell {
diff --git a/templates/flake/.envrc b/templates/flake/.envrc
index 9ee556b1..1faf1bb0 100644
--- a/templates/flake/.envrc
+++ b/templates/flake/.envrc
@@ -1,4 +1,5 @@
+# shellcheck shell=bash
 if ! has nix_direnv_version || ! nix_direnv_version 3.0.5; then
-    source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/3.0.5/direnvrc" "sha256-RuwIS+QKFj/T9M2TFXScjBsLR6V3A17YVoEW/Q6AZ1w="
+  source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/3.0.5/direnvrc" "sha256-RuwIS+QKFj/T9M2TFXScjBsLR6V3A17YVoEW/Q6AZ1w="
 fi
 use flake
diff --git a/templates/flake/flake.nix b/templates/flake/flake.nix
index 6a518689..f7b7e5f1 100644
--- a/templates/flake/flake.nix
+++ b/templates/flake/flake.nix
@@ -3,14 +3,15 @@
   inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
   inputs.flake-utils.url = "github:numtide/flake-utils";
 
-  outputs = { nixpkgs, flake-utils, ... }:
-    flake-utils.lib.eachDefaultSystem (system:
+  outputs =
+    { nixpkgs, flake-utils, ... }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
       let
         pkgs = nixpkgs.legacyPackages.${system};
       in
       {
-        devShells.default = pkgs.mkShell {
-          packages = [ pkgs.bashInteractive ];
-        };
-      });
+        devShells.default = pkgs.mkShell { packages = [ pkgs.bashInteractive ]; };
+      }
+    );
 }
diff --git a/test-runner.nix b/test-runner.nix
index f25e2960..5ff22da0 100644
--- a/test-runner.nix
+++ b/test-runner.nix
@@ -1,15 +1,23 @@
-{ writeShellScriptBin
-, direnv
-, python3
-, lib
-, coreutils
-, gnugrep
-, nixVersions
-, nixVersion
+{
+  writeShellScriptBin,
+  direnv,
+  python3,
+  lib,
+  coreutils,
+  gnugrep,
+  nixVersions,
+  nixVersion,
 }:
 writeShellScriptBin "test-runner-${nixVersion}" ''
   set -e
-  export PATH=${lib.makeBinPath [ direnv nixVersions.${nixVersion} coreutils gnugrep ]}
+  export PATH=${
+    lib.makeBinPath [
+      direnv
+      nixVersions.${nixVersion}
+      coreutils
+      gnugrep
+    ]
+  }
 
   echo run unittest
   ${lib.getExe' python3.pkgs.pytest "pytest"} .
diff --git a/tests/testenv/flake.nix b/tests/testenv/flake.nix
index 516e6ba8..fb67fa1a 100644
--- a/tests/testenv/flake.nix
+++ b/tests/testenv/flake.nix
@@ -4,10 +4,9 @@
   inputs.flake-utils.url = "github:numtide/flake-utils";
 
   # deadnix: skip
-  outputs = { self, nixpkgs, flake-utils }:
+  outputs =
+    { nixpkgs, flake-utils, ... }:
     flake-utils.lib.eachDefaultSystem (system: {
-      devShell = import ./shell.nix {
-        pkgs = nixpkgs.legacyPackages.${system};
-      };
+      devShell = import ./shell.nix { pkgs = nixpkgs.legacyPackages.${system}; };
     });
 }
diff --git a/tests/testenv/shell.nix b/tests/testenv/shell.nix
index ebd6af50..1ee82c1f 100644
--- a/tests/testenv/shell.nix
+++ b/tests/testenv/shell.nix
@@ -1,8 +1,9 @@
-{ pkgs ? import (builtins.getFlake (toString ./.)).inputs.nixpkgs { }
-, someArg ? null
-, shellHook ? ''
+{
+  pkgs ? import (builtins.getFlake (toString ./.)).inputs.nixpkgs { },
+  someArg ? null,
+  shellHook ? ''
     echo "Executing shellHook."
-  ''
+  '',
 }:
 pkgs.mkShellNoCC {
   inherit shellHook;
@@ -10,5 +11,7 @@ pkgs.mkShellNoCC {
   nativeBuildInputs = [ pkgs.hello ];
   SHOULD_BE_SET = someArg;
 
-  passthru = { subshell = pkgs.mkShellNoCC { THIS_IS_A_SUBSHELL = "OK"; }; };
+  passthru = {
+    subshell = pkgs.mkShellNoCC { THIS_IS_A_SUBSHELL = "OK"; };
+  };
 }
diff --git a/treefmt.nix b/treefmt.nix
index 66167a0a..415c2051 100644
--- a/treefmt.nix
+++ b/treefmt.nix
@@ -1,33 +1,32 @@
-{ inputs, ... }: {
-  imports = [
-    inputs.treefmt-nix.flakeModule
-  ];
+{ inputs, ... }:
+{
+  imports = [ inputs.treefmt-nix.flakeModule ];
 
-  perSystem = {
-    treefmt = {
-      # Used to find the project root
-      projectRootFile = ".git/config";
+  perSystem =
+    { pkgs, ... }:
+    {
+      treefmt = {
+        # Used to find the project root
+        projectRootFile = ".git/config";
 
-      programs = {
-        deadnix.enable = true;
-        deno.enable = true;
-        mypy.enable = true;
-        ruff.check = true;
-        ruff.format = true;
-        nixpkgs-fmt.enable = true;
-        shellcheck.enable = true;
-        shfmt.enable = true;
-        statix.enable = true;
-      };
+        programs = {
+          deadnix.enable = true;
+          deno.enable = true;
+          mypy.enable = true;
+          ruff.check = true;
+          ruff.format = true;
+          nixfmt.enable = true;
+          nixfmt.package = pkgs.nixfmt-rfc-style;
+          shellcheck.enable = true;
+          shfmt.enable = true;
+          statix.enable = true;
+          yamlfmt.enable = true;
+        };
 
-      settings.formatter =
-        let
-          shellIncludes = [ "*.sh" "direnvrc" ];
-        in
-        {
-          shellcheck.includes = shellIncludes;
-          shfmt.includes = shellIncludes;
+        settings.formatter = {
+          shellcheck.includes = [ "direnvrc" ];
+          shfmt.includes = [ "direnvrc" ];
         };
+      };
     };
-  };
 }