diff --git a/home/variables.nix b/home/variables.nix
index d0477b8..4080ef4 100644
--- a/home/variables.nix
+++ b/home/variables.nix
@@ -1,5 +1,6 @@
 {config, ...}: {
   home.sessionVariables = {
+    # https://github.com/b3nj5m1n/xdg-ninja
     ZDOTDIR = "${config.xdg.configHome}/zsh";
     GIT_CONFIG_GLOBAL = "${config.xdg.configHome}/git/config";
     PYTHONSTARTUP = "${config.xdg.configHome}/python/pythonrc.py";
diff --git a/modules/homebrew.nix b/modules/homebrew.nix
index deca46a..dc5a12b 100644
--- a/modules/homebrew.nix
+++ b/modules/homebrew.nix
@@ -1,4 +1,5 @@
 _: {
+  # https://docs.brew.sh/Manpage#environment
   environment.variables = {
     HOMEBREW_NO_ANALYTICS = "1";
     HOMEBREW_NO_INSECURE_REDIRECT = "1";
diff --git a/system.nix b/system.nix
index 4464de7..f48b692 100644
--- a/system.nix
+++ b/system.nix
@@ -9,6 +9,8 @@
     ./modules/homebrew.nix
   ];
 
+  # https://daiderd.com/nix-darwin/manual/index.html#sec-options
+
   system = {
     defaults = {
       dock = {
@@ -30,6 +32,7 @@
 
   security.pam.enableSudoTouchIdAuth = true;
 
+  # https://github.com/ryanccn/nix-darwin-custom-icons
   environment.customIcons = {
     enable = true;
     icons = [