diff --git a/metropolis/node/tools/tools.go b/metropolis/node/tools/tools.go
index aec9de4..5377496 100644
--- a/metropolis/node/tools/tools.go
+++ b/metropolis/node/tools/tools.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 //go:build tools
 // +build tools