diff --git a/src/bootstrap/src/core/build_steps/run.rs b/src/bootstrap/src/core/build_steps/run.rs
index 7028bffea54..0a428ec5ca0 100644
--- a/src/bootstrap/src/core/build_steps/run.rs
+++ b/src/bootstrap/src/core/build_steps/run.rs
@@ -1,3 +1,8 @@
+//! Build-and-run steps for in-repo tools
+//!
+//! A bit of a hodge-podge as e.g. if a tool's a test fixture it should be in `build_steps::test`.
+//! If it can be reached from `./x.py run` it can go here.
+
 use std::path::PathBuf;
 use std::process::Command;