diff --git a/toy-impl/README.md b/toy-impl/README.md
index a197f01..20931dc 100644
--- a/toy-impl/README.md
+++ b/toy-impl/README.md
@@ -231,3 +231,7 @@ We currently support:
     * `__xor__`
     * `__neg__`
 
+## Builtin Functions
+* `len(list[X]) -> int32`
+* `range(int32) -> list[int32]`
+