diff --git a/patacrep/tools/cache/__init__.py b/patacrep/tools/cache/__init__.py
index e69de29b..15c1f745 100644
--- a/patacrep/tools/cache/__init__.py
+++ b/patacrep/tools/cache/__init__.py
@@ -0,0 +1 @@
+"""Perform operations on cache."""
diff --git a/patacrep/tools/content/__init__.py b/patacrep/tools/content/__init__.py
index e69de29b..854a40ba 100644
--- a/patacrep/tools/content/__init__.py
+++ b/patacrep/tools/content/__init__.py
@@ -0,0 +1 @@
+"""Perform operations on songbook content."""
diff --git a/patacrep/tools/convert/__init__.py b/patacrep/tools/convert/__init__.py
index e69de29b..754935e9 100644
--- a/patacrep/tools/convert/__init__.py
+++ b/patacrep/tools/convert/__init__.py
@@ -0,0 +1 @@
+"""Convert between song formats."""