diff --git a/doc/doc.md b/doc/doc.md
index 138387e..c59d46a 100644
--- a/doc/doc.md
+++ b/doc/doc.md
@@ -193,3 +193,14 @@ not to do it. This can be done by holding special keys while selecting:
 | `Option`+`Mouse` | iTerm2, Hyper |
 | `Fn`+`Mouse`     | Terminal.app  |
 | `Shift`+`Mouse`  | Linux         |
+
+
+## Configs
+
+Next configs available for fx via environment variables.
+
+| Name           | Values                                    | Description                                           |
+|----------------|-------------------------------------------|-------------------------------------------------------|
+| `FX_LANG`      | `js`, `node`, `python`, `python3`, `ruby` | Reducer type.                                         |
+| `FX_THEME`     | `0..9`                                    | Color theme.                                          |
+| `FX_SHOW_SIZE` | `true` or `false`                         | Show size of arrays and object in collapsed previews. |