diff --git a/template/filters.py b/template/filters.py
index 018c9ac0422ab8a6a5ebf2e5949a4ce689a088ee..993435afa6ee1a96ef97e15a8d1e3c2b9d1a5f90 100644
--- a/template/filters.py
+++ b/template/filters.py
@@ -2,6 +2,19 @@
 
 
 def to_yaml(value):
+    '''
+    Converts given data structure to YAML form.
+    Examples:
+
+    >>> to_yaml([1,2,3])
+    '[1, 2, 3]\\n'
+    >>> to_yaml({'a': 1, 'b': 2})
+    '{a: 1, b: 2}\\n'
+    >>> to_yaml({1: {'a': [1,2,3]}})
+    '1:\\n  a: [1, 2, 3]\\n'
+    >>> to_yaml("abc")
+    'abc\\n...\\n'
+    '''
     from yaml import safe_dump
     return safe_dump(value)
 
diff --git a/tox.ini b/tox.ini
index 1ac57a887f6c612dbaf002ad645ccde42423948f..c1b9865a58b02fbac3790291c3eca13be6b87662 100644
--- a/tox.ini
+++ b/tox.ini
@@ -21,6 +21,7 @@ commands =
     check-manifest --ignore tox.ini,tests*
     python setup.py check -m -r -s
     flake8 .
+    python -m doctest template/filters.py template/__init__.py
     ./tests.sh
 
 [testenv:release]