diff --git a/src/generation.py b/src/generation.py
index 32e1bdc..a998c3f 100644
--- a/src/generation.py
+++ b/src/generation.py
@@ -7,6 +7,7 @@
 import torch
 
 from src.sample import sample
+from src.tokenizer import CharLevelTokenizer
 from src.utils import print_rank_0
 
 
@@ -32,11 +33,20 @@ def generate(
         stop_at_eos=True,
         max_seqlen=None,
     ):
-        eos_token_ids = self.tokenizer.tokenize(self.tokenizer.eos).to(device)
+        if isinstance(self.tokenizer.eos, int):
+            eos_token_ids = torch.LongTensor([self.tokenizer.eos]).to(device)
+        else:
+            # is a tensor
+            eos_token_ids = self.tokenizer.tokenize(self.tokenizer.eos).to(device)
 
         if input_ids is None:
             input = self.tokenizer.tokenize(input_string)
-            input = input.unsqueeze(0).to(device)
+            if isinstance(input, list):
+                input = torch.LongTensor(input).unsqueeze(0).to(device)
+            # is a tensor
+            else:
+                input = input.unsqueeze(0).to(device)
+
         else:
             input = input_ids
         x = input
@@ -96,10 +106,12 @@ def generate(
                     inference_params_dict_out["mha"].seqlen_offset += 1
                     inference_params_dict_out["hyena"].seqlen_offset += 1
 
-            logits, inference_params_dict_out = self.model(
-                x,
-                inference_params_dict=inference_params_dict_out,
-            )
+            # do forward pass with no gradient
+            with torch.no_grad():
+                logits, inference_params_dict_out = self.model(
+                    x,
+                    inference_params_dict=inference_params_dict_out,
+                )
 
             last_logits = logits[:, -1]
 
@@ -113,7 +125,7 @@ def generate(
             if stop_at_eos and (generation[0, -2:] == eos_token_ids).all():
                 print_rank_0("Stopping generation at EOS")
 
-            if print_generation and verbose:
+            if print_generation and verbose and batch_size == 1:
                 print_rank_0(
                     f"{self.tokenizer.detokenize([new_idx.item()])}",
                     end=" ",
@@ -128,10 +140,10 @@ def generate(
                 x = torch.cat([x, new_idx[:, None]], dim=-1)
 
         if verbose:
-            y = self.tokenizer.detokenize_batch(
-                generation[:, : i + 1],
-                skip_special_tokens=skip_special_tokens,
-            )
+            kwargs = {}
+            if not isinstance(self.tokenizer, CharLevelTokenizer):
+                kwargs["skip_special_tokens"] = skip_special_tokens
+            y = self.tokenizer.detokenize_batch(generation[:, : i + 1], **kwargs)
 
             for until in self.untils:
                 if until in y:
diff --git a/src/tokenizer.py b/src/tokenizer.py
index 6792c94..ed25d72 100644
--- a/src/tokenizer.py
+++ b/src/tokenizer.py
@@ -1,7 +1,10 @@
 # based on https://github.com/EleutherAI/gpt-neox/blob/main/megatron/tokenizer/tokenizer.py
 import json
 import pathlib
+from abc import ABC, abstractmethod
+from typing import List, Union
 
+import numpy as np
 import torch
 import tqdm
 from tokenizers import Tokenizer
@@ -67,3 +70,115 @@ def eod(self):
     @property
     def vocab_size(self):
         return 32000
+
+
+class AbstractTokenizer(ABC):
+    """Abstract class for tokenizer."""
+
+    def __init__(self, name):
+        self.name = name
+        super().__init__()
+
+    @property
+    @abstractmethod
+    def vocab_size(self):
+        pass
+
+    @property
+    @abstractmethod
+    def vocab(self):
+        """Dictionary from vocab text token to id token."""
+        pass
+
+    @property
+    @abstractmethod
+    def inv_vocab(self):
+        """Dictionary from vocab id token to text token."""
+        pass
+
+    @abstractmethod
+    def tokenize(self, text):
+        pass
+
+    def detokenize(self, token_ids):
+        raise NotImplementedError("detokenizer is not implemented for {} " "tokenizer".format(self.name))
+
+    @property
+    def cls(self):
+        raise NotImplementedError("CLS is not provided for {} " "tokenizer".format(self.name))
+
+    @property
+    def sep(self):
+        raise NotImplementedError("SEP is not provided for {} " "tokenizer".format(self.name))
+
+    @property
+    def pad(self):
+        raise NotImplementedError("PAD is not provided for {} " "tokenizer".format(self.name))
+
+    @property
+    def eod(self):
+        raise NotImplementedError("EOD is not provided for {} " "tokenizer".format(self.name))
+
+    @property
+    def mask(self):
+        raise NotImplementedError("MASK is not provided for {} " "tokenizer".format(self.name))
+
+
+class CharLevelTokenizer(AbstractTokenizer):
+    """Character Level Tokenizer"""
+
+    def __init__(self, vocab_size):
+        name = "CharLevelTokenizer"
+        super().__init__(name)
+        self._vocab_size = vocab_size
+        self.eod_id = 0
+        self.eos_id = 0
+        self.pad_id = 1
+
+    def clamp(self, n):
+        return max(32, min(n, self.vocab_size))
+
+    @property
+    def vocab_size(self):
+        return self._vocab_size
+
+    @property
+    def vocab(self):
+        raise NotImplementedError
+
+    @property
+    def inv_vocab(self):
+        raise NotImplementedError
+
+    def decode_token(self, token: int):
+        return str(chr(self.clamp(token)))
+
+    def tokenize(self, text: str):
+        return list(np.fromstring(text, dtype=np.uint8))
+
+    def tokenize_batch(self, text_batch: Union[List[str], str]):
+        if isinstance(text_batch, list):
+            return [self.tokenize(s) for s in text_batch]
+        else:
+            return self.tokenize(text_batch)
+
+    def detokenize(self, token_ids):
+        return "".join(list(map(self.decode_token, token_ids)))
+
+    def detokenize_batch(self, token_ids: Union[List[str], str]):
+        if isinstance(token_ids, list):
+            return [self.detokenize(s) for s in token_ids]
+        # elif if tensor, convert to list first
+        elif isinstance(token_ids, torch.Tensor):
+            return [self.detokenize(s) for s in token_ids.tolist()]
+        else:
+            return self.detokenize(token_ids)
+
+    @property
+    def eod(self):
+        return self.eod_id
+
+    # duplicate to suppose both names, eos and eod
+    @property
+    def eos(self):
+        return self.eod_id