diff --git a/fedbiomed/common/training_args.py b/fedbiomed/common/training_args.py
index ee9171ab0..e9a8451f3 100644
--- a/fedbiomed/common/training_args.py
+++ b/fedbiomed/common/training_args.py
@@ -79,7 +79,7 @@ def __init__(self, ta: Dict = None, extra_scheme: Dict = None, only_required: bo
     # validators
     @staticmethod
     @validator_decorator
-    def _metric_validation_hook( metric: Union[MetricTypes, str, None] ):
+    def _metric_validation_hook( metric: Union[MetricTypes, str, None] ) -> Union[bool, str]:
         """
         Validate the metric argument of test_metric.
         """
@@ -99,7 +99,7 @@ def _metric_validation_hook( metric: Union[MetricTypes, str, None] ):
 
     @staticmethod
     @validator_decorator
-    def _test_ratio_hook( v: Any):
+    def _test_ratio_hook( v: Any) -> bool:
         """
         Test if in [ 0.0 , 1.0]  interval.
         """
@@ -110,7 +110,7 @@ def _test_ratio_hook( v: Any):
 
     @staticmethod
     @validator_decorator
-    def _loss_rate_hook( v: Any):
+    def _loss_rate_hook( v: Any) -> bool:
         """
         Test if lr is greater than 0.
         """
@@ -264,7 +264,7 @@ def __getitem__(self, key: str) -> Any:
 
     def update(self, values: Dict) -> TypeVar("TrainingArgs"):
         """
-        Update multiple keys of the trainig arguments.
+        Update multiple keys of the training arguments.
 
         Args:
             values:  a dictionnary of keys to validate/update
@@ -290,9 +290,9 @@ def __ixor__(self, other: Dict) -> TypeVar("TrainingArgs"):
         t ^= { 'epochs': 2 , 'lr': 0.01 }
         ```
         Args:
-            other:  a dictionnary of keys to validate/update
+            other (Dict):  a dictionnary of keys to validate/update
 
-        Return:
+        Returns:
             the object itself after modification
 
         Raises:
@@ -318,7 +318,7 @@ def default_value(self, key: str) -> Any:
         Returns the default value for the key.
 
         Args:
-            key:  key
+            key (str):  key
 
         Returns:
             value: the default value associated to the key
@@ -341,7 +341,7 @@ def default_value(self, key: str) -> Any:
             raise FedbiomedUserInputError(msg)
 
 
-    def dict(self):
+    def dict(self) -> Dict:
         """Returns the training_args as a dictionnary."""
 
         if 'test_metric' in self._ta and \
diff --git a/fedbiomed/common/validator.py b/fedbiomed/common/validator.py
index c6101440b..63c0cb2fa 100755
--- a/fedbiomed/common/validator.py
+++ b/fedbiomed/common/validator.py
@@ -37,13 +37,13 @@ def my_validation_funct( value ):
 This class provides json validation against a scheme describing the
 expected json content.
 
-The scheme need to follow a specific format, which describe each
+The scheme needs to follow a specific format, which describes each
 allowed fields and their characteristics:
 - a list of associated validators to check against (aka Validator instances)
 - the field requirement (required on not)
 - a default value (which will be used if the field is required but not provided)
 
-A SchemeValidator is accepted byt the Validator class.
+A SchemeValidator is accepted by the Validator class.
 
 **Typical example:**
 
@@ -243,7 +243,7 @@ def validate(self, value: Dict) -> bool:
         Validate a value against the scheme passed at creation time.
 
         Args:
-             value:  value (json) to validate against the scheme passed
+             value (dict):  value (json) to validate against the scheme passed
                      at __init__
         Returns:
             True if value is valid
@@ -279,20 +279,20 @@ def populate_with_defaults(self, value: Dict, only_required: bool = True) -> Dic
         """
         Inject default values defined in the rule to a given dictionary.
 
-        Parse the given json value and add default value is key was required
+        Parse the given json value and add default value if key was required
         but not provided.
-        Of course, the default value must be provided in the scheme.
+        Of course, the default values must be provided in the scheme.
 
         Warning: this does not parse the result against the scheme. It has
         to be done by the user.
 
         Args:
-            value:   a json data to verify/populate
-            only_required: if True, only force required key. If False, update all
-                           keys with default values in the scheme
+            value (dict):   a json data to verify/populate
+            only_required (bool): if True, only force required key. If False, update all
+                           keys with default values in the scheme. Defaults to True.
 
         Return:
-            a json populated with default values, returns an empty dict if something is wrong
+            (dict) a json populated with default values, returns an empty dict if something is wrong
 
         Raises:
             RuleError: if scheme provided at init contains a required rules without default value
@@ -449,7 +449,7 @@ def validate(self, value: Any, rule: Any, strict: bool = True) -> bool:
             True if rule exists and value is compliant.
 
         Raises:
-            ValidateError: if provided value does not com[ly to the rule
+            ValidateError: if provided value does not comply to the rule
         """
         # rule is in the rulebook -> execute the rule associated function
         if isinstance(rule, str) and rule in self._validation_rulebook:
@@ -605,13 +605,13 @@ def register(self, rule: str, hook: Any, override: bool = False) -> bool:
         Add a rule/validation_function to the rulebook.
 
         if the rule (entry of the catalog) was already registered,
-        it will be rejected, except if ovverride is True
+        it will be rejected, except if override is True
 
         Args:
             rule:      registration name (string)
             hook:      validation hook to register (the hook is checked against
                        the accepted hook types)
-            override:  if True, still register the rule even if it existed
+            override:  if True, still register the rule even if it existed. Defaults to False.
 
         Returns:
             True if rule is accepted, False instead if rule exists and overrride is False
diff --git a/tests/test_validator.py b/tests/test_validator.py
index 01921c929..5edd8c40a 100644
--- a/tests/test_validator.py
+++ b/tests/test_validator.py
@@ -1,3 +1,4 @@
+from typing import Tuple
 import unittest
 from fedbiomed.common.validator import Validator, SchemeValidator, \
     validator_decorator, _ValidatorHookType
@@ -20,7 +21,7 @@ def tearDown(self):
     # define some validation hooks to add to the validator
     @staticmethod
     @validator_decorator
-    def hook_01_positive_integer_check(value):
+    def hook_01_positive_integer_check(value) -> bool:
         """
         value must be a positive integer
         """
@@ -29,7 +30,7 @@ def hook_01_positive_integer_check(value):
         return True
 
     @staticmethod
-    def hook_02_positive_integer_check(value):
+    def hook_02_positive_integer_check(value) -> Tuple[bool, str]:
         """
         value must be a positive integer