diff --git a/khaosz/trainer/train_callback.py b/khaosz/trainer/train_callback.py
index 7f351ad..dcb868e 100644
--- a/khaosz/trainer/train_callback.py
+++ b/khaosz/trainer/train_callback.py
@@ -2,7 +2,7 @@ import os
 from tqdm import tqdm
 from torch.nn.utils import clip_grad_norm_
 from torch.optim.lr_scheduler import LambdaLR
-from typing import Optional, TYPE_CHECKING
+from typing import Optional, Protocol, TYPE_CHECKING
 from khaosz.trainer.strategy import ScheduleConfig, SchedulerFactory
 
 if TYPE_CHECKING:
@@ -10,43 +10,34 @@ if TYPE_CHECKING:
     from khaosz.trainer.train_context import TrainContext
 
 
-class TrainCallback:
+class TrainCallback(Protocol):
     """ 
     Callback interface for trainer.
-    and we use '_' to ignore unused parameters.
     """
 
     def on_train_begin(self, trainer: 'Trainer', context: 'TrainContext'):
         """ Called at the beginning of training. """
-        _ = trainer, context
     
-    def on_train_begin(self, trainer: 'Trainer', context: 'TrainContext'):
+    def on_train_end(self, trainer: 'Trainer', context: 'TrainContext'):
         """ Called at the end of training. """
-        _ = trainer, context
 
-    def on_train_begin(self, trainer: 'Trainer', context: 'TrainContext'):
+    def on_epoch_begin(self, trainer: 'Trainer', context: 'TrainContext'):
         """ Called at the beginning of each epoch. """
-        _ = trainer, context
 
-    def on_train_begin(self, trainer: 'Trainer', context: 'TrainContext'):
+    def on_epoch_end(self, trainer: 'Trainer', context: 'TrainContext'):
         """  Called at the end of each epoch. """
-        _ = trainer, context
-
-    def on_train_begin(self, trainer: 'Trainer', context: 'TrainContext'):
-        """ Called at the beginning of each batch. """
-        _ = trainer, context
-
-    def on_train_begin(self, trainer: 'Trainer', context: 'TrainContext'):
-        """ Called at the end of each batch. """
-        _ = trainer, context
-
-    def on_train_begin(self, trainer: 'Trainer', context: 'TrainContext'):
+    
+    def on_step_begin(self, trainer: 'Trainer', context: 'TrainContext'):
         """ Called at the beginning of each step. """
-        _ = trainer, context
 
-    def on_train_begin(self, trainer: 'Trainer', context: 'TrainContext'):
+    def on_step_end(self, trainer: 'Trainer', context: 'TrainContext'):
         """ Called at the end of each step."""
-        _ = trainer, context
+
+    def on_batch_begin(self, trainer: 'Trainer', context: 'TrainContext'):
+        """ Called at the beginning of each batch. """
+
+    def on_batch_end(self, trainer: 'Trainer', context: 'TrainContext'):
+        """ Called at the end of each batch. """
 
 
 class ProgressBarCallback(TrainCallback):