diff --git a/src/amplitude_experiment/client.py b/src/amplitude_experiment/client.py
index ee6b421..32e237c 100644
--- a/src/amplitude_experiment/client.py
+++ b/src/amplitude_experiment/client.py
@@ -1,35 +1,78 @@
+import time
+from time import sleep
 from .config import Config
 from .version import __version__
 from .variant import Variant
+from .user import User
 import http.client
 import json
+import logging
 
 
 class Client:
+    """Main client for fetching variant data."""
+
     def __init__(self, api_key, config=None):
+        """
+        Creates a new Experiment Client instance.
+            Parameters:
+                api_key (str): The environment API Key
+                config (Config): Config Object
+
+            Returns:
+                Experiment Client instance.
+        """
+        if not api_key:
+            raise ValueError("Experiment API key is empty")
         self.api_key = api_key
         self.config = config or Config()
+        self.logger = logging.getLogger("Amplitude")
+        self.logger.addHandler(logging.StreamHandler())
+        if self.config.debug:
+            self.logger.setLevel(logging.DEBUG)
+
+    def fetch(self, user: User):
+        """
+        Fetch all variants for a user synchronous.This method will automatically retry if configured.
+            Parameters:
+                user (User): The Experiment User
 
-    def fetch(self, user):
+            Returns:
+                Variants Dictionary.
+        """
         try:
             return self.fetch_internal(user)
-        except:
-            print("[Experiment] Failed to fetch variants")
+        except Exception as e:
+            self.logger.error(f"[Experiment] Failed to fetch variants: {e}")
             return {}
 
     def fetch_internal(self, user):
+        self.logger.debug(f"[Experiment] Fetching variants for user: {user}")
         try:
             return self.do_fetch(user, self.config.fetch_timeout_millis)
-        except:
-            print("Experiment] Fetch failed")
+        except Exception as e:
+            self.logger.error(f"Experiment] Fetch failed: {e}")
             return self.retry_fetch(user)
 
     def retry_fetch(self, user):
         if self.config.fetch_retries == 0:
             return {}
-        pass
+        self.logger.debug("[Experiment] Retrying fetch")
+        err = None
+        delay_millis = self.config.fetch_retry_backoff_min_millis
+        for i in range(self.config.fetch_retries):
+            sleep(delay_millis / 1000.0)
+            try:
+                return self.do_fetch(user, self.config.fetch_timeout_millis)
+            except Exception as e:
+                self.logger.error(f"[Experiment] Retry failed: {e}")
+                err = e
+            delay_millis = min(delay_millis * self.config.fetch_retry_backoff_scalar,
+                               self.config.fetch_retry_backoff_max_millis)
+        raise err
 
     def do_fetch(self, user, timeout_millis):
+        start = time.time()
         user_context = self.add_context(user)
         headers = {
             'Authorization': f"Api-Key {self.api_key}",
@@ -40,10 +83,17 @@ def do_fetch(self, user, timeout_millis):
         conn = Connection(host)
         conn.connect()
         body = user_context.to_json().encode('utf8')
+        if len(body) > 8000:
+            self.logger.warning(f"[Experiment] encoded user object length ${len(body)} "
+                                f"cannot be cached by CDN; must be < 8KB")
+        self.logger.debug(f"[Experiment] Fetch variants for user: {str(user_context)}")
         conn.request('POST', '/sdk/vardata', body, headers)
         response = conn.getresponse()
+        elapsed = '%.3f' % ((time.time() - start) * 1000)
+        self.logger.debug(f"[Experiment] Fetch complete in {elapsed} ms")
         json_response = json.loads(response.read().decode("utf8"))
         variants = self.parse_json_variants(json_response)
+        self.logger.debug(f"[Experiment] Fetched variants: {json.dumps(variants, default=str)}")
         conn.close()
         return variants
 
diff --git a/src/amplitude_experiment/config.py b/src/amplitude_experiment/config.py
index 46bb319..6b6e729 100644
--- a/src/amplitude_experiment/config.py
+++ b/src/amplitude_experiment/config.py
@@ -1,4 +1,6 @@
 class Config:
+    """Experiment Client Configuration"""
+
     DEFAULT_SERVER_URL = 'https://api.lab.amplitude.com'
 
     def __init__(self, debug=False,
@@ -9,6 +11,24 @@ def __init__(self, debug=False,
                  fetch_retry_backoff_max_millis=10000,
                  fetch_retry_backoff_scalar=1.5,
                  fetch_retry_timeout_millis=10000):
+        """
+        Initialize a config
+            Parameters:
+                debug (str): Set to true to log some extra information to the console.
+                server_url (str): The server endpoint from which to request variants.
+                fetch_timeout_millis (int): The request timeout, in milliseconds, used when fetching variants
+                  triggered by calling start() or setUser().
+                fetch_retries (int): The number of retries to attempt before failing.
+                fetch_retry_backoff_min_millis (int): Retry backoff minimum (starting backoff delay) in milliseconds.
+                  The minimum backoff is scaled by `fetch_retry_backoff_scalar` after each retry failure.
+                fetch_retry_backoff_max_millis (int): Retry backoff maximum in milliseconds. If the scaled backoff is
+                  greater than the max, the max is used for all subsequent retries.
+                fetch_retry_backoff_scalar (float): Scales the minimum backoff exponentially.
+                fetch_retry_timeout_millis (int): The request timeout for retrying fetch requests.
+
+            Returns:
+                The config object
+        """
         self.debug = debug
         self.server_url = server_url
         self.fetch_timeout_millis = fetch_timeout_millis
diff --git a/src/amplitude_experiment/user.py b/src/amplitude_experiment/user.py
index ad1410b..ab53249 100644
--- a/src/amplitude_experiment/user.py
+++ b/src/amplitude_experiment/user.py
@@ -2,9 +2,36 @@
 
 
 class User:
+    """
+    Defines a user context for evaluation. `device_id` and `user_id` are used for identity resolution.
+    All other predefined fields and user properties are used for rule based user targeting.
+    """
     def __init__(self, device_id=None, user_id=None, country=None, city=None, region=None, dma=None,
                  language=None, platform=None, version=None, os=None, device_manufacturer=None, device_brand=None,
                  device_model=None, carrier=None, library=None, user_properties=None):
+        """
+        Initialize User instance
+            Parameters:
+                device_id (str): Device ID for associating with an identity in Amplitude
+                user_id (str): User ID for associating with an identity in Amplitude
+                country (str): Predefined field, must be manually provided
+                city (str): Predefined field, must be manually provided
+                region (str): Predefined field, must be manually provided
+                dma (str): Predefined field, must be manually provided
+                language (str): Predefined field, must be manually provided
+                platform (str): Predefined field, must be manually provided
+                version (str): Predefined field, must be manually provided
+                os (str): Predefined field, must be manually provided
+                device_manufacturer (str): Predefined field, must be manually provided
+                device_brand (str): Predefined field, must be manually provided
+                device_model (str): Predefined field, must be manually provided
+                carrier (str): Predefined field, must be manually provided
+                library (str): Predefined field, must be manually provided
+                user_properties (dict): Custom user properties
+
+            Returns:
+                User object
+        """
         self.device_id = device_id
         self.user_id = user_id
         self.country = country
@@ -23,4 +50,9 @@ def __init__(self, device_id=None, user_id=None, country=None, city=None, region
         self.user_properties = user_properties
 
     def to_json(self):
+        """Return user information as JSON string."""
         return json.dumps(self, default=lambda o: o.__dict__)
+
+    def __str__(self):
+        """Return user as string"""
+        return self.to_json()
diff --git a/src/amplitude_experiment/variant.py b/src/amplitude_experiment/variant.py
index 2c6821e..6861a07 100644
--- a/src/amplitude_experiment/variant.py
+++ b/src/amplitude_experiment/variant.py
@@ -1,8 +1,30 @@
 class Variant:
+    """Variant Class"""
 
-    def __init__(self, value, payload):
+    def __init__(self, value: str, payload=None):
+        """
+        Initialize a Variant
+            Parameters:
+                value (str): The value of the variant determined by the flag configuration.
+                payload (Any): The attached payload, if any.
+
+            Returns:
+                Experiment User context containing a device_id and user_id (if available)
+        """
         self.value = value
         self.payload = payload
 
-    def __eq__(self, obj):
+    def __eq__(self, obj) -> bool:
+        """
+        Determine if current variant equal other variant
+            Parameters:
+                obj (Variant): The variant to compare with
+
+            Returns:
+                True if two variant equals, otherwise False
+        """
         return self.value == obj.value and self.payload == obj.payload
+
+    def __str__(self):
+        """Return Variant as string"""
+        return f"value: {self.value}, payload: {self.payload}"
diff --git a/tests/client_test.py b/tests/client_test.py
index dc1f954..fcb3d75 100644
--- a/tests/client_test.py
+++ b/tests/client_test.py
@@ -1,6 +1,6 @@
 import unittest
 
-from src.amplitude_experiment import Client, Variant, User
+from src.amplitude_experiment import Client, Variant, User, Config
 
 API_KEY = 'client-DvWljIjiiuqLbyjqdvBaLFfEBrAvGuA3'
 SERVER_URL = 'https://api.lab.amplitude.com/sdk/vardata'
@@ -8,6 +8,9 @@
 
 class ClientTestCase(unittest.TestCase):
 
+    def test_initialize_raise_error(self):
+        self.assertRaises(ValueError, Client, "")
+
     def test_fetch(self):
         client = Client(API_KEY)
         expected_variant = Variant('on', 'payload')