diff --git a/modules/installer/tools/nixos-option.sh b/modules/installer/tools/nixos-option.sh
new file mode 100644
index 00000000000..5195ed8cf69
--- /dev/null
+++ b/modules/installer/tools/nixos-option.sh
@@ -0,0 +1,164 @@
+#! @shell@ -e
+
+# Allow the location of NixOS sources and the system configuration
+# file to be overridden.
+: ${NIXOS_PATH=/etc/nixos/nixos}
+: ${NIXOS=/etc/nixos/nixos}
+: ${NIXPKGS=/etc/nixos/nixpkgs}
+: ${NIXOS_CONFIG=/etc/nixos/configuration.nix}
+export NIXOS_PATH
+
+usage () {
+  echo 1>&2 "
+Usage: $0 OPTION_NAME [-v] [-d] [-l]
+
+This program is used to explore NixOS options by looking at their values or
+by looking at their description.  It is helpful for understanding the how
+your configuration is working.
+
+Options:
+
+  -v | --value          Display the current value, based on your
+                        configuration.
+  -d | --default        Display the default value, the example and the
+                        description.
+  -l | --lookup         Display where the option is defined and where it
+                        is declared.
+  --help                Show this message.
+
+Environment variables affecting nixos-option:
+
+  \$NIXOS_PATH          Path where the NixOS repository is located.
+  \$NIXOS_CONFIG        Path to your configuration file.
+  \$NIXPKGS             Path to Nix packages.
+
+"
+
+  exit 1;
+}
+
+#####################
+# Process Arguments #
+#####################
+
+desc=false
+defs=false
+value=false
+verbose=false
+
+option=""
+
+argfun=""
+for arg; do
+  if test -z "$argfun"; then
+    case $arg in
+      -d|--description) desc=true;;
+      -v|--value) value=true;;
+      -l|--lookup) defs=true;;
+      --verbose) verbose=true;;
+      --help) usage;;
+      -*) usage;;
+      *) if test -z "$option"; then
+           option="$arg"
+         else
+           usage
+         fi;;
+    esac
+  else
+    case $argfun in
+      set_*)
+        var=$(echo $argfun | sed 's,^set_,,')
+        eval $var=$arg
+        ;;
+    esac
+    argfun=""
+  fi
+done
+
+if ! $defs && ! $desc; then
+  value=true
+fi
+
+if $verbose; then
+  set -x
+else
+  set +x
+fi
+
+#############################
+# Process the configuration #
+#############################
+
+evalAttr(){
+  local prefix=$1
+  local suffix=$2
+  local strict=$3
+  echo "(import $NIXOS_PATH {}).$prefix${option:+.$option}${suffix:+.$suffix}" |
+    nix-instantiate - --eval-only ${strict:+--strict}
+}
+
+evalOpt(){
+  evalAttr "eval.options" "$@"
+}
+
+evalCfg(){
+  evalAttr "config" "$@"
+}
+
+findSources(){
+  local suffix=$1
+  echo "builtins.map (f: f.source) (import $NIXOS_PATH {}).eval.options${option:+.$option}.$suffix" |
+    nix-instantiate - --eval-only --strict
+}
+
+
+
+if test "$(evalOpt "_type" 2> /dev/null)" = '"option"'; then
+  $value && evalCfg;
+
+  if $desc; then
+    $value && echo;
+
+    if default=$(evalOpt "default" - 2> /dev/null); then
+      echo "Default: $default"
+    else
+      echo "Default: <None>"
+    fi
+    if example=$(evalOpt "example" - 2> /dev/null); then
+      echo "Example: $example"
+    fi
+    echo "Description:"
+    eval printf $(evalOpt "description")
+  fi
+
+  if $defs; then
+    $desc || $value && echo;
+
+    echo "Declared by:"
+    for f in $(findSources "declarations"); do
+      test $f = '[' -o $f = ']' && continue;
+      echo "  $f"
+    done
+    echo ""
+    echo "Defined by:"
+    for f in $(findSources "definitions"); do
+      test $f = '[' -o $f = ']' && continue;
+      echo "  $f"
+    done
+    echo ""
+  fi
+
+else
+  # echo 1>&2 "Warning: This value is not an option."
+
+  result=$(evalCfg)
+  if names=$(echo "builtins.attrNames $result" | sed 's,<CODE>,"<CODE>",g' | nix-instantiate - --eval-only --strict 2> /dev/null); then
+    echo 1>&2 "This attribute set contains:" 
+    for attr in $names; do
+      test $attr = '[' -o $attr = ']' && continue;
+      eval echo $attr # escape extra double-quotes in the attribute name.
+    done
+  else
+    echo $result
+  fi
+fi
diff --git a/modules/installer/tools/tools.nix b/modules/installer/tools/tools.nix
index 7a0e8dbf936..9785cfe0db5 100644
--- a/modules/installer/tools/tools.nix
+++ b/modules/installer/tools/tools.nix
@@ -111,6 +111,11 @@ let
     inherit (pkgs) perl;
   };
 
+  nixosOption = makeProg {
+    name = "nixos-option";
+    src = ./nixos-option.sh;
+  };
+
 in
 
 {
@@ -121,6 +126,7 @@ in
       nixosRebuild
       nixosHardwareScan
       nixosGenSeccureKeys
+      nixosOption
 
       installer2.runInChroot
       installer2.nixosPrepareInstall