diff --git a/csv_metadata_quality/__main__.py b/csv_metadata_quality/__main__.py
index b7ad319..3905311 100644
--- a/csv_metadata_quality/__main__.py
+++ b/csv_metadata_quality/__main__.py
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: GPL-3.0-only
+
 from sys import argv
 
 from csv_metadata_quality import app
diff --git a/csv_metadata_quality/app.py b/csv_metadata_quality/app.py
index 36111ca..5a02680 100644
--- a/csv_metadata_quality/app.py
+++ b/csv_metadata_quality/app.py
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: GPL-3.0-only
+
 import argparse
 import re
 import signal
diff --git a/csv_metadata_quality/check.py b/csv_metadata_quality/check.py
index 7c0355b..b396418 100755
--- a/csv_metadata_quality/check.py
+++ b/csv_metadata_quality/check.py
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: GPL-3.0-only
+
 import os
 import re
 from datetime import datetime, timedelta
diff --git a/csv_metadata_quality/experimental.py b/csv_metadata_quality/experimental.py
index 1444115..c3593e4 100644
--- a/csv_metadata_quality/experimental.py
+++ b/csv_metadata_quality/experimental.py
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: GPL-3.0-only
+
 import re
 
 import langid
diff --git a/csv_metadata_quality/fix.py b/csv_metadata_quality/fix.py
index c4d741d..deb7da0 100755
--- a/csv_metadata_quality/fix.py
+++ b/csv_metadata_quality/fix.py
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: GPL-3.0-only
+
 import re
 from unicodedata import normalize
 
diff --git a/csv_metadata_quality/util.py b/csv_metadata_quality/util.py
index 32b0dbe..2490090 100644
--- a/csv_metadata_quality/util.py
+++ b/csv_metadata_quality/util.py
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: GPL-3.0-only
+
 from ftfy.badness import sequence_weirdness
 
 
diff --git a/csv_metadata_quality/version.py b/csv_metadata_quality/version.py
index a784b59..af197cb 100644
--- a/csv_metadata_quality/version.py
+++ b/csv_metadata_quality/version.py
@@ -1 +1,3 @@
+# SPDX-License-Identifier: GPL-3.0-only
+
 VERSION = "0.4.8-dev"
diff --git a/tests/test_check.py b/tests/test_check.py
index aeeaca2..485abee 100644
--- a/tests/test_check.py
+++ b/tests/test_check.py
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: GPL-3.0-only
+
 import pandas as pd
 from colorama import Fore
 
diff --git a/tests/test_fix.py b/tests/test_fix.py
index 4155301..9ecba75 100644
--- a/tests/test_fix.py
+++ b/tests/test_fix.py
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: GPL-3.0-only
+
 import csv_metadata_quality.fix as fix