{
  perSystem =
    { pkgs, ... }:
    {
      treefmt = {
        programs = {
          nixfmt = {
            enable = true;
            excludes = [ "_sources/*.nix" ];
          };
          biome = {
            enable = true;
            includes = [ "*.json" ];
            excludes = [ "_sources/*.json" ];
            settings = {
              javascript.formatter.enabled = false;
              css.formatter.enabled = false;
            };
          };
          dprint = {
            enable = true;
            includes = [
              "*.md"
              "*.toml"
              "*.yaml"
            ];
            excludes = [ "secrets/*.yaml" ];
            settings = {
              plugins = pkgs.dprint-plugins.getPluginList (
                plugins: with plugins; [
                  dprint-plugin-toml
                  dprint-plugin-markdown
                  g-plane-pretty_yaml
                ]
              );
            };
          };
          just = {
            enable = true;
            includes = [ ".justfile" ];
          };
          typos =
            let
              config = ./.typos.toml |> builtins.readFile |> builtins.fromTOML;
            in
            {
              enable = true;
              includes = [ "*" ];
              excludes = [ "assets/*" ] ++ config.files.extend-exclude;
              configFile = toString ./.typos.toml;
              # Disable all extra option in treefmt module.
              # Use config file.
              sort = false;
              isolated = false;
              hidden = false;
              noIgnore = false;
              noIgnoreDot = false;
              noIgnoreGlobal = false;
              noIgnoreParent = false;
              noIgnoreVCS = false;
              binary = false;
              noCheckFilenames = false;
              noCheckFiles = false;
              noUnicode = false;
            };
        };
      };
    };
}