diff --git a/tools/clean.py b/tools/clean.py
index 9753469aa..92de461a3 100644
--- a/tools/clean.py
+++ b/tools/clean.py
@@ -12,7 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-"""Clean up script for build artifacts."""
+"""Clean up script for build artifacts.
+
+Only really intended to be used by internal build scripts.
+"""
 
 import os
 try: