diff --git a/lib/tfw/fsm/yaml_fsm.py b/lib/tfw/fsm/yaml_fsm.py
index d6c266d..fbfc542 100644
--- a/lib/tfw/fsm/yaml_fsm.py
+++ b/lib/tfw/fsm/yaml_fsm.py
@@ -13,7 +13,17 @@ from tfw.fsm.fsm_base import FSMBase
 
 
 class YamlFSM(FSMBase):
+    """
+    This is a state machine capable of building itself from a YAML config file.
+    """
     def __init__(self, config_file, jinja2_variables=None):
+        """
+        :param config_file: path of the YAML file
+        :param jinja2_variables: dict containing jinja2 variables
+                                 or str with filename of YAML file to
+                                 parse and use as dict.
+                                 jinja2 support is disabled if this is None
+        """
         self.config = ConfigParser(config_file, jinja2_variables).config
         self.setup_states()
         super().__init__()  # FSMBase.__init__() requires states