diff --git a/build/toolbase/doc.go b/build/toolbase/doc.go
index 8bf9e25..065d96f 100644
--- a/build/toolbase/doc.go
+++ b/build/toolbase/doc.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 // toolbase implements common functionality for tools operating on a Monogon
 // workspace, notably CI and developer tools.
 package toolbase
diff --git a/build/toolbase/gotoolchain/toolchain_test.go b/build/toolbase/gotoolchain/toolchain_test.go
index 7b93d6d..2f13d80 100644
--- a/build/toolbase/gotoolchain/toolchain_test.go
+++ b/build/toolbase/gotoolchain/toolchain_test.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 package gotoolchain
 
 import (
diff --git a/build/toolbase/label.go b/build/toolbase/label.go
index 5d033b3..a16860d 100644
--- a/build/toolbase/label.go
+++ b/build/toolbase/label.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 package toolbase
 
 import (
diff --git a/build/toolbase/label_test.go b/build/toolbase/label_test.go
index e16d88f..558edae 100644
--- a/build/toolbase/label_test.go
+++ b/build/toolbase/label_test.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 package toolbase
 
 import (
diff --git a/build/toolbase/workspace.go b/build/toolbase/workspace.go
index f1d9f08..5213504 100644
--- a/build/toolbase/workspace.go
+++ b/build/toolbase/workspace.go
@@ -1,3 +1,6 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
 package toolbase
 
 import (