diff --git a/canvas/README.vars b/canvas/README.vars
new file mode 100644
index 000000000000..141c88fbe5f2
--- /dev/null
+++ b/canvas/README.vars
@@ -0,0 +1,6 @@
+Environment variables in canvas:
+
+vclcanvas
+---------
+
+CANVAS_SPRITE_BOUNDS - draw green lines as sprite bounds