diff --git a/xtask/src/main.rs b/xtask/src/main.rs
index eb39bf7159a..04dca402c19 100644
--- a/xtask/src/main.rs
+++ b/xtask/src/main.rs
@@ -1,5 +1,12 @@
-//! FIXME: write short doc here
-
+//! See https://github.com/matklad/cargo-xtask/.
+//!
+//! This binary defines various auxiliary build commands, which are not
+//! expressible with just `cargo`. Notably, it provides `cargo xtask codegen`
+//! for code genetaiont and `cargo xtask install` for installation of
+//! rust-analyzer server and client.
+//!
+//! This binary is integrated into the `cargo` command line by using an alias in
+//! `.cargo/config`.
 mod help;
 
 use core::fmt::Write;