diff --git a/errcron/cronjob.py b/errcron/cronjob.py
index <HASH>..<HASH> 100644
--- a/errcron/cronjob.py
+++ b/errcron/cronjob.py
@@ -4,9 +4,20 @@
 
 
 class CronJob(object):
+    """Job runner for errcron, handling job running trigger and action
+    """
     def __init__(self):
-        self.trigger_time = None
         self.trigger_format = None
+        """datetime format by trigger to run job"""
+        self.trigger_time = None
+        """datetime value by trigger to run job"""
 
     def is_runnable(self, time):
+        """Check whether job run action at specified time
+
+        :param time: Time to run action
+        :type time: datetime.datetime
+        :return: Job is runnable or not
+        :rtype: boolean
+        """
         return time.strftime(self.trigger_format) == self.trigger_time
Refactor: Add docstrings