diff --git a/xtask/src/ast_src.rs b/xtask/src/ast_src.rs
index 2d9ae904b12..98d8104e59c 100644
--- a/xtask/src/ast_src.rs
+++ b/xtask/src/ast_src.rs
@@ -1,3 +1,5 @@
+//! Defines input for code generation process.
+
 pub(crate) struct KindsSrc<'a> {
     pub(crate) punct: &'a [(&'a str, &'a str)],
     pub(crate) keywords: &'a [&'a str],
diff --git a/xtask/src/codegen/gen_assists_docs.rs b/xtask/src/codegen/gen_assists_docs.rs
index 697e830df40..6da5ca89e7f 100644
--- a/xtask/src/codegen/gen_assists_docs.rs
+++ b/xtask/src/codegen/gen_assists_docs.rs
@@ -1,3 +1,5 @@
+//! Generates `assists.md` documentation.
+
 use std::{fs, path::Path};
 
 use crate::{
diff --git a/xtask/src/lib.rs b/xtask/src/lib.rs
index 2bcd76d60b0..e5da726ac21 100644
--- a/xtask/src/lib.rs
+++ b/xtask/src/lib.rs
@@ -1,4 +1,6 @@
-//! FIXME: write short doc here
+//! Support library for `cargo xtask` command.
+//!
+//! See https://github.com/matklad/cargo-xtask/
 
 pub mod not_bash;
 pub mod install;
diff --git a/xtask/src/not_bash.rs b/xtask/src/not_bash.rs
index c49ad671d52..40f706d9f87 100644
--- a/xtask/src/not_bash.rs
+++ b/xtask/src/not_bash.rs
@@ -1,4 +1,5 @@
 //! A bad shell -- small cross platform module for writing glue code
+
 use std::{
     cell::RefCell,
     env,