diff --git a/astrai/dataset/__init__.py b/astrai/dataset/__init__.py
index c42d532..7341607 100644
--- a/astrai/dataset/__init__.py
+++ b/astrai/dataset/__init__.py
@@ -1,19 +1,37 @@
 from astrai.dataset.dataset import (
     BaseDataset,
-    BaseSegmentFetcher,
     DatasetFactory,
-    MultiSegmentFetcher,
 )
 from astrai.dataset.sampler import ResumableDistributedSampler
+from astrai.dataset.storage import (
+    BaseSegmentFetcher,
+    BaseStorage,
+    H5Storage,
+    JSONStorage,
+    MultiSegmentFetcher,
+    available_storage_types,
+    create_storage,
+    detect_format,
+    load_h5,
+    load_json,
+    save_h5,
+    save_json,
+)
 
 __all__ = [
-    # Base classes
     "BaseDataset",
-    # Factory
     "DatasetFactory",
-    # Fetchers
     "BaseSegmentFetcher",
     "MultiSegmentFetcher",
-    # Sampler
+    "BaseStorage",
+    "H5Storage",
+    "JSONStorage",
+    "create_storage",
+    "detect_format",
+    "available_storage_types",
+    "save_h5",
+    "load_h5",
+    "save_json",
+    "load_json",
     "ResumableDistributedSampler",
 ]
diff --git a/astrai/dataset/dataset.py b/astrai/dataset/dataset.py
index 1a49b62..31920ff 100644
--- a/astrai/dataset/dataset.py
+++ b/astrai/dataset/dataset.py
@@ -1,140 +1,72 @@
 """Dataset implementations with factory pattern for training."""
 
-import bisect
 from abc import ABC, abstractmethod
-from typing import Dict, List, Optional, Union
+from typing import Dict, List, Optional
 
 import torch
 from torch import Tensor
 from torch.utils.data import Dataset
 
+from astrai.dataset.storage import (
+    BaseStorage,
+    create_storage,
+    detect_format,
+)
 from astrai.factory import BaseFactory
-from astrai.serialization import load_h5
-
-
-class BaseSegmentFetcher:
-    """Fetches data segments across multiple tensor segments.
-
-    Maintains cumulative lengths for efficient range queries across
-    multiple discontinuous segments.
-    """
-
-    def __init__(self, segments: List[Tensor]):
-        self.segments = segments
-        self.cum_lengths = []
-
-        total = 0
-        for seg in segments:
-            total += torch.numel(seg)
-            self.cum_lengths.append(total)
-
-        self.total_length = total
-
-    def __len__(self) -> int:
-        return self.total_length
-
-    def fetch_data(self, begin_idx: int, end_idx: int) -> Tensor:
-        """Fetch data in the range [begin_idx, end_idx).
-
-        Args:
-            begin_idx: Starting index (inclusive)
-            end_idx: Ending index (exclusive)
-
-        Returns:
-            Concatenated tensor of data in the specified range
-        """
-        if not (
-            0 <= begin_idx < self.total_length and 0 <= end_idx <= self.total_length
-        ):
-            raise ValueError("begin_idx or end_idx out of bounds")
-        if begin_idx >= end_idx:
-            return torch.tensor([], dtype=torch.long)
-
-        # Find segment boundaries for the range
-        seg_start_idx = bisect.bisect_right(self.cum_lengths, begin_idx)
-        seg_end_idx = bisect.bisect_left(self.cum_lengths, end_idx)
-
-        result_segments = []
-
-        for i in range(seg_start_idx, seg_end_idx + 1):
-            prev_cum = self.cum_lengths[i - 1] if i > 0 else 0
-            start = max(begin_idx - prev_cum, 0)
-            end = min(end_idx - prev_cum, len(self.segments[i]))
-            data = self.segments[i][start:end]
-            result_segments.append(data)
-
-        return torch.cat(result_segments, dim=0)
-
-
-class MultiSegmentFetcher:
-    """Manages multiple segment fetchers for different data keys.
-
-    Each key corresponds to a different type of data (e.g., "sequence", "mask").
-    """
-
-    def __init__(self, multi_segments: Dict):
-        self.multi_keys = list(multi_segments.keys())
-        self.multi_fetchers = {
-            key: BaseSegmentFetcher(segments)
-            for key, segments in multi_segments.items()
-        }
-
-    def __len__(self) -> int:
-        """Returns the minimum length across all fetchers."""
-        len_list = [len(seg) for seg in self.multi_fetchers.values()]
-        return min(len_list)
-
-    def key_fetch(
-        self, begin_idx: int, end_idx: int, keys: Union[str, List[str]]
-    ) -> Dict:
-        """Fetch data for specific keys.
-
-        Args:
-            begin_idx: Starting index
-            end_idx: Ending index
-            keys: Single key or list of keys to fetch
-
-        Returns:
-            Dictionary of tensors if multiple keys, single tensor if one key
-        """
-        fetch_dict = {}
-        keys = [keys] if isinstance(keys, str) else keys
-
-        for key in keys:
-            fetcher = self.multi_fetchers[key]
-            fetch_tensor = fetcher.fetch_data(begin_idx, end_idx)
-            fetch_dict[key] = fetch_tensor
-
-        return fetch_dict if len(keys) > 1 else fetch_dict[keys[0]]
-
-    def fetch_data(self, begin_idx: int, end_idx: int) -> Dict:
-        """Fetch all keys."""
-        return self.key_fetch(begin_idx, end_idx, self.multi_keys)
 
 
 class BaseDataset(Dataset, ABC):
     """Abstract base class for all dataset types.
 
     Implements common functionality for window-based data fetching.
+    Uses a storage abstraction for format-agnostic data loading.
     """
 
     def __init__(self, window_size: int, stride: int):
         super().__init__()
-        self.segments = {}
         self.window_size = window_size
         self.stride = stride
-        self.total_samples = None
-        self.fetcher: Optional[MultiSegmentFetcher] = None
+        self.storage: Optional[BaseStorage] = None
 
-    def load(self, load_path: str):
-        """Load dataset from HDF5 file.
+    def load(self, load_path: str, storage_type: Optional[str] = None, tokenizer=None):
+        """Load dataset from the given path.
+
+        Auto-detects the storage format if not specified.
 
         Args:
-            load_path: Path to the HDF5 data file
+            load_path: Path to the data directory or file
+            storage_type: Force a specific storage type ("h5", "json"),
+                          or None for auto-detection
+            tokenizer: Callable str -> List[int], used to tokenize raw text
+                       in JSON files. Ignored for HDF5.
         """
-        self.segments = load_h5(load_path)
-        self.fetcher = MultiSegmentFetcher(self.segments)
-        self.total_samples = len(self.fetcher)
+        if storage_type is None:
+            storage_type = detect_format(load_path)
+        self.storage = create_storage(storage_type)
+        self.storage.load(load_path, tokenizer=tokenizer)
+
+    def load_json(self, load_path: str, tokenizer=None):
+        """Load dataset from JSON files explicitly.
+
+        Args:
+            load_path: Path to the JSON data file or directory
+            tokenizer: Optional tokenizer callable for raw text JSON.
+        """
+        self.load(load_path, storage_type="json", tokenizer=tokenizer)
+
+    @property
+    def count(self) -> int:
+        """Return the total number of raw elements (tokens) in the dataset."""
+        if self.storage is None:
+            return 0
+        return len(self.storage)
+
+    @property
+    def keys(self) -> List[str]:
+        """Return the available data keys."""
+        if self.storage is None:
+            return []
+        return self.storage.keys
 
     def get_index(self, index: int) -> tuple:
         """Calculate begin and end indices for a sample.
@@ -145,10 +77,12 @@ class BaseDataset(Dataset, ABC):
         Returns:
             Tuple of (begin_idx, end_idx)
         """
-        assert self.total_samples > self.window_size
+        assert self.storage is not None
+        total = len(self.storage)
+        assert total > self.window_size
 
-        begin_idx = min(index * self.stride, self.total_samples - 1 - self.window_size)
-        end_idx = min(begin_idx + self.window_size, self.total_samples - 1)
+        begin_idx = min(index * self.stride, total - 1 - self.window_size)
+        end_idx = min(begin_idx + self.window_size, total - 1)
 
         return begin_idx, end_idx
 
@@ -161,10 +95,11 @@ class BaseDataset(Dataset, ABC):
         raise NotImplementedError
 
     def __len__(self) -> int:
-        assert self.total_samples is not None
-        if self.total_samples <= self.window_size:
+        assert self.storage is not None
+        total = len(self.storage)
+        if total <= self.window_size:
             return 0
-        return (self.total_samples - 1 - self.window_size) // self.stride + 1
+        return (total - 1 - self.window_size) // self.stride + 1
 
 
 class DatasetFactory(BaseFactory["BaseDataset"]):
@@ -209,6 +144,8 @@ class DatasetFactory(BaseFactory["BaseDataset"]):
         load_path: str,
         window_size: int,
         stride: Optional[int] = None,
+        storage_type: Optional[str] = None,
+        tokenizer=None,
     ) -> "BaseDataset":
         """Create and load a dataset in one step.
 
@@ -217,6 +154,8 @@ class DatasetFactory(BaseFactory["BaseDataset"]):
             load_path: Path to the data file
             window_size: Window size for data sampling
             stride: Stride between consecutive samples (default: same as window_size)
+            storage_type: Storage type ("h5", "json") or None for auto-detection
+            tokenizer: Callable str -> List[int] for raw text JSON tokenization
 
         Returns:
             Loaded dataset instance
@@ -225,7 +164,7 @@ class DatasetFactory(BaseFactory["BaseDataset"]):
             stride = window_size
 
         dataset = cls.create(train_type, window_size, stride)
-        dataset.load(load_path)
+        dataset.load(load_path, storage_type=storage_type, tokenizer=tokenizer)
 
         return dataset
 
@@ -235,10 +174,6 @@ class DatasetFactory(BaseFactory["BaseDataset"]):
         return cls.list_registered()
 
 
-# ============== Dataset Classes ==============
-# All dataset classes are registered at class definition time using the decorator
-
-
 @DatasetFactory.register("seq")
 class SEQDataset(BaseDataset):
     """Dataset for sequential next-token prediction training."""
@@ -247,7 +182,7 @@ class SEQDataset(BaseDataset):
         super().__init__(window_size, stride)
 
     def _fetch_data(self, begin_idx: int, end_idx: int) -> Tensor:
-        return self.fetcher.key_fetch(begin_idx, end_idx, "sequence")
+        return self.storage.fetch(begin_idx, end_idx, "sequence")
 
     def __getitem__(self, index):
         begin_idx, end_idx = self.get_index(index)
@@ -266,7 +201,7 @@ class SFTDataset(BaseDataset):
         super().__init__(window_size, stride)
 
     def _fetch_data(self, begin_idx: int, end_idx: int, key: str) -> Tensor:
-        return self.fetcher.key_fetch(begin_idx, end_idx, key)
+        return self.storage.fetch(begin_idx, end_idx, key)
 
     def __getitem__(self, index):
         begin_idx, end_idx = self.get_index(index)
@@ -290,7 +225,7 @@ class DPODataset(BaseDataset):
         super().__init__(window_size, stride)
 
     def _fetch_data(self, begin_idx: int, end_idx: int, key: str) -> Tensor:
-        return self.fetcher.key_fetch(begin_idx, end_idx, key)
+        return self.storage.fetch(begin_idx, end_idx, key)
 
     def __getitem__(self, index: int):
         begin_idx, end_idx = self.get_index(index)
@@ -320,7 +255,7 @@ class GRPODataset(BaseDataset):
         super().__init__(window_size, stride)
 
     def _fetch_data(self, begin_idx: int, end_idx: int, key: str) -> Tensor:
-        return self.fetcher.key_fetch(begin_idx, end_idx, key)
+        return self.storage.fetch(begin_idx, end_idx, key)
 
     def __getitem__(self, index: int) -> Dict[str, Tensor]:
         begin_idx, end_idx = self.get_index(index)
diff --git a/astrai/dataset/storage.py b/astrai/dataset/storage.py
new file mode 100644
index 0000000..d1699a6
--- /dev/null
+++ b/astrai/dataset/storage.py
@@ -0,0 +1,310 @@
+"""Storage backends for different data formats.
+
+Each storage handles format-specific loading (HDF5, JSON, etc.) and provides
+a uniform interface for data access and length observation via fetchers.
+"""
+
+import bisect
+import json
+import os
+from abc import ABC, abstractmethod
+from pathlib import Path
+from typing import Callable, Dict, List, Optional, Union
+
+import h5py
+import torch
+from torch import Tensor
+
+
+def save_h5(file_path: str, file_name: str, tensor_group: Dict[str, List[Tensor]]):
+    os.makedirs(file_path, exist_ok=True)
+    full_file_path = os.path.join(file_path, f"{file_name}.h5")
+    with h5py.File(full_file_path, "w") as f:
+        for key, tensors in tensor_group.items():
+            grp = f.create_group(key)
+            for idx, tensor in enumerate(tensors):
+                arr = tensor.cpu().numpy()
+                grp.create_dataset(f"data_{idx}", data=arr)
+
+
+def load_h5(file_path: str, share_memory=True) -> Dict[str, List[Tensor]]:
+    tensor_group: Dict[str, List[Tensor]] = {}
+
+    root_path = Path(file_path)
+    h5_files = list(root_path.rglob("*.h5")) + list(root_path.rglob("*.hdf5"))
+
+    for h5_file in h5_files:
+        with h5py.File(h5_file, "r") as f:
+            for key in f.keys():
+                grp = f[key]
+                dsets = []
+                for dset_name in grp.keys():
+                    dset = grp[dset_name]
+                    tensor = torch.from_numpy(dset[:])
+                    if share_memory:
+                        tensor = tensor.share_memory_()
+                    dsets.append(tensor)
+
+                if tensor_group.get(key) is None:
+                    tensor_group[key] = []
+                tensor_group[key].extend(dsets)
+
+    return tensor_group
+
+
+def save_json(file_path: str, file_name: str, tensor_group: Dict[str, List[Tensor]]):
+    os.makedirs(file_path, exist_ok=True)
+    full_file_path = os.path.join(file_path, f"{file_name}.json")
+    json_data = {}
+    for key, tensors in tensor_group.items():
+        json_data[key] = [tensor.tolist() for tensor in tensors]
+    with open(full_file_path, "w", encoding="utf-8") as f:
+        json.dump(json_data, f, ensure_ascii=False)
+
+
+def load_json(
+    file_path: str,
+    share_memory: bool = True,
+    tokenizer: Optional[Callable[[str], List[int]]] = None,
+) -> Dict[str, List[Tensor]]:
+    """Load tensor data from JSON files.
+
+    Supports two modes:
+    - Pre-tokenized: JSON values are List[List[int]] (token IDs), loaded as-is.
+    - Raw text: JSON values are List[str], tokenized via ``tokenizer`` callable
+      at load time. A ``tokenizer`` receives a str and returns List[int].
+
+    Non-data JSON files (e.g. config.json) with scalar/object values are
+    silently skipped.
+    """
+    tensor_group: Dict[str, List[Tensor]] = {}
+    root_path = Path(file_path)
+    json_files = list(root_path.rglob("*.json")) + list(root_path.rglob("*.jsonl"))
+    for json_file in json_files:
+        with open(json_file, "r", encoding="utf-8") as f:
+            data = json.load(f)
+        if not isinstance(data, dict):
+            continue
+        for key, sequences in data.items():
+            if not isinstance(sequences, list):
+                continue
+            tensors = []
+            for seq in sequences:
+                if tokenizer is not None and isinstance(seq, str):
+                    seq = tokenizer(seq)
+                tensor = torch.tensor(seq, dtype=torch.long)
+                if share_memory:
+                    tensor = tensor.share_memory_()
+                tensors.append(tensor)
+            if tensor_group.get(key) is None:
+                tensor_group[key] = []
+            tensor_group[key].extend(tensors)
+    return tensor_group
+
+
+def detect_format(load_path: str) -> str:
+    """Auto-detect storage format from files in the directory.
+
+    Args:
+        load_path: Directory or file path
+
+    Returns:
+        Format string ("h5" or "json")
+
+    Raises:
+        FileNotFoundError: If no supported data files are found
+    """
+    root = Path(load_path)
+    if root.is_file():
+        suffix = root.suffix.lower()
+        if suffix in (".h5", ".hdf5"):
+            return "h5"
+        if suffix in (".json", ".jsonl"):
+            return "json"
+        raise ValueError(f"Unsupported file format: {suffix}")
+
+    h5_files = list(root.rglob("*.h5")) + list(root.rglob("*.hdf5"))
+    if h5_files:
+        return "h5"
+    json_files = list(root.rglob("*.json")) + list(root.rglob("*.jsonl"))
+    if json_files:
+        return "json"
+    raise FileNotFoundError(f"No supported data files found at {load_path}")
+
+
+class BaseSegmentFetcher:
+    """Fetches data segments across multiple tensor segments.
+
+    Maintains cumulative lengths for efficient range queries across
+    multiple discontinuous segments.
+    """
+
+    def __init__(self, segments: List[Tensor]):
+        self.segments = segments
+        self.cum_lengths = []
+
+        total = 0
+        for seg in segments:
+            total += torch.numel(seg)
+            self.cum_lengths.append(total)
+
+        self.total_length = total
+
+    def __len__(self) -> int:
+        return self.total_length
+
+    def fetch_data(self, begin_idx: int, end_idx: int) -> Tensor:
+        """Fetch data in the range [begin_idx, end_idx)."""
+        if not (
+            0 <= begin_idx < self.total_length and 0 <= end_idx <= self.total_length
+        ):
+            raise ValueError("begin_idx or end_idx out of bounds")
+        if begin_idx >= end_idx:
+            return torch.tensor([], dtype=torch.long)
+
+        seg_start_idx = bisect.bisect_right(self.cum_lengths, begin_idx)
+        seg_end_idx = bisect.bisect_left(self.cum_lengths, end_idx)
+
+        result_segments = []
+
+        for i in range(seg_start_idx, seg_end_idx + 1):
+            prev_cum = self.cum_lengths[i - 1] if i > 0 else 0
+            start = max(begin_idx - prev_cum, 0)
+            end = min(end_idx - prev_cum, len(self.segments[i]))
+            result_segments.append(self.segments[i][start:end])
+
+        return torch.cat(result_segments, dim=0)
+
+
+class MultiSegmentFetcher:
+    """Manages multiple segment fetchers for different data keys."""
+
+    def __init__(self, multi_segments: Dict):
+        self.multi_keys = list(multi_segments.keys())
+        self.multi_fetchers = {
+            key: BaseSegmentFetcher(segments)
+            for key, segments in multi_segments.items()
+        }
+
+    def __len__(self) -> int:
+        """Returns the minimum length across all fetchers."""
+        len_list = [len(seg) for seg in self.multi_fetchers.values()]
+        return min(len_list)
+
+    def key_fetch(
+        self, begin_idx: int, end_idx: int, keys: Union[str, List[str]]
+    ) -> Dict:
+        """Fetch data for specific keys."""
+        fetch_dict = {}
+        keys = [keys] if isinstance(keys, str) else keys
+
+        for key in keys:
+            fetcher = self.multi_fetchers[key]
+            fetch_tensor = fetcher.fetch_data(begin_idx, end_idx)
+            fetch_dict[key] = fetch_tensor
+
+        return fetch_dict if len(keys) > 1 else fetch_dict[keys[0]]
+
+    def fetch_data(self, begin_idx: int, end_idx: int) -> Dict:
+        """Fetch all keys."""
+        return self.key_fetch(begin_idx, end_idx, self.multi_keys)
+
+
+class BaseStorage(ABC):
+    """Abstract storage backend for loading and dispatching data.
+
+    Storage encapsulates format-specific loading and provides a uniform
+    interface for data access and length observation. Subclasses handle
+    different data formats (HDF5, JSON, etc.) while exposing the same
+    fetch interface.
+    """
+
+    def __init__(self):
+        self._fetcher: Optional[MultiSegmentFetcher] = None
+
+    @abstractmethod
+    def load(self, load_path: str, tokenizer=None) -> None:
+        """Load data from the given path into internal fetcher."""
+        raise NotImplementedError
+
+    def __len__(self) -> int:
+        """Total number of raw elements (tokens) in storage."""
+        if self._fetcher is None:
+            return 0
+        return len(self._fetcher)
+
+    def fetch(self, begin_idx: int, end_idx: int, keys: Union[str, List[str]]):
+        """Fetch data for the given keys and index range.
+
+        Args:
+            begin_idx: Starting index (inclusive)
+            end_idx: Ending index (exclusive)
+            keys: Single key or list of keys to fetch
+
+        Returns:
+            Tensor if single key, Dict[str, Tensor] if multiple keys
+        """
+        if self._fetcher is None:
+            raise RuntimeError("Storage not loaded")
+        return self._fetcher.key_fetch(begin_idx, end_idx, keys)
+
+    @property
+    def keys(self) -> List[str]:
+        """Return the data keys available in this storage."""
+        if self._fetcher is None:
+            return []
+        return self._fetcher.multi_keys
+
+
+class H5Storage(BaseStorage):
+    """HDF5-based storage backend (pre-tokenized data)."""
+
+    def load(self, load_path: str, tokenizer=None) -> None:
+        segments = load_h5(load_path)
+        self._fetcher = MultiSegmentFetcher(segments)
+
+
+class JSONStorage(BaseStorage):
+    """JSON-based storage backend.
+
+    Supports two modes:
+    - Pre-tokenized: JSON values are List[List[int]], loaded as-is.
+    - Raw text: JSON values are List[str], tokenized via ``tokenizer``
+      callable (str -> List[int]) at load time.
+    """
+
+    def load(self, load_path: str, tokenizer=None) -> None:
+        segments = load_json(load_path, tokenizer=tokenizer)
+        self._fetcher = MultiSegmentFetcher(segments)
+
+
+_STORAGE_REGISTRY: Dict[str, type] = {
+    "h5": H5Storage,
+    "json": JSONStorage,
+}
+
+
+def create_storage(storage_type: str) -> BaseStorage:
+    """Create a storage instance by type name.
+
+    Args:
+        storage_type: Storage type name ("h5", "json")
+
+    Returns:
+        Storage instance
+
+    Raises:
+        ValueError: If the storage type is unknown
+    """
+    storage_cls = _STORAGE_REGISTRY.get(storage_type)
+    if storage_cls is None:
+        raise ValueError(
+            f"Unknown storage type: '{storage_type}'. "
+            f"Available: {sorted(_STORAGE_REGISTRY.keys())}"
+        )
+    return storage_cls()
+
+
+def available_storage_types() -> List[str]:
+    """Return list of registered storage type names."""
+    return sorted(_STORAGE_REGISTRY.keys())
diff --git a/astrai/serialization.py b/astrai/serialization.py
index ba0aab4..87b4272 100644
--- a/astrai/serialization.py
+++ b/astrai/serialization.py
@@ -1,53 +1,14 @@
 import json
-import os
 from pathlib import Path
-from typing import Any, Dict, List, Optional
+from typing import Any, Dict, Optional
 
-import h5py
 import safetensors.torch as st
 import torch
 import torch.distributed as dist
-from torch import Tensor
 
 from astrai.parallel.setup import get_rank
 
 
-def save_h5(file_path: str, file_name: str, tensor_group: Dict[str, List[Tensor]]):
-    os.makedirs(file_path, exist_ok=True)
-    full_file_path = os.path.join(file_path, f"{file_name}.h5")
-    with h5py.File(full_file_path, "w") as f:
-        for key, tensors in tensor_group.items():
-            grp = f.create_group(key)
-            for idx, tensor in enumerate(tensors):
-                arr = tensor.cpu().numpy()
-                grp.create_dataset(f"data_{idx}", data=arr)
-
-
-def load_h5(file_path: str, share_memory=True) -> Dict[str, List[Tensor]]:
-    tensor_group: Dict[str, List[Tensor]] = {}
-
-    root_path = Path(file_path)
-    h5_files = list(root_path.rglob("*.h5")) + list(root_path.rglob("*.hdf5"))
-
-    for h5_file in h5_files:
-        with h5py.File(h5_file, "r") as f:
-            for key in f.keys():
-                grp = f[key]
-                dsets = []
-                for dset_name in grp.keys():
-                    dset = grp[dset_name]
-                    tensor = torch.from_numpy(dset[:])
-                    if share_memory:
-                        tensor = tensor.share_memory_()
-                    dsets.append(tensor)
-
-                if tensor_group.get(key) is None:
-                    tensor_group[key] = []
-                tensor_group[key].extend(dsets)
-
-    return tensor_group
-
-
 class Checkpoint:
     def __init__(
         self,
diff --git a/tests/data/test_dataset.py b/tests/data/test_dataset.py
index bb1d94c..5a35b25 100644
--- a/tests/data/test_dataset.py
+++ b/tests/data/test_dataset.py
@@ -1,8 +1,11 @@
+import json
+import os
+
 import numpy as np
 import torch
 
 from astrai.dataset.dataset import DatasetFactory
-from astrai.serialization import save_h5
+from astrai.dataset.storage import save_h5
 
 
 def test_dataset_loader_random_paths(base_test_env):
@@ -64,7 +67,7 @@ def test_dpo_strategy_with_random_data(base_test_env):
     )
 
     assert dpo_dataset is not None
-    assert hasattr(dpo_dataset, "fetcher")
+    assert dpo_dataset.storage is not None
     assert len(dpo_dataset) > 0
 
     # Test that we can get DPO items without errors
@@ -100,7 +103,7 @@ def test_sft_dataset_with_random_data(base_test_env):
     )
 
     assert sft_dataset is not None
-    assert hasattr(sft_dataset, "fetcher")
+    assert sft_dataset.storage is not None
     assert len(sft_dataset) > 0
 
     # Test that we can get SFT items without errors
@@ -143,3 +146,139 @@ def test_dataset_with_custom_stride(base_test_env):
     )
 
     assert len(dataset) > len(default_stride_dataset)
+
+
+# ============== JSON Storage Tests (raw text + tokenizer) ==============
+
+
+def _make_tokenizer_fn(tokenizer):
+    """Wrap tokenizer.encode() as a str -> List[int] callable."""
+    return lambda text: tokenizer.encode(text, add_special_tokens=False)
+
+
+def test_seq_dataset_from_json_text(base_test_env):
+    """Test loading SEQ dataset from raw-text JSON with tokenizer"""
+    tokenizer = base_test_env["tokenizer"]
+    tokenizer_fn = _make_tokenizer_fn(tokenizer)
+    test_dir = base_test_env["test_dir"]
+    data_dir = os.path.join(test_dir, "json_text")
+    os.makedirs(data_dir, exist_ok=True)
+
+    texts = [
+        "hello world this is a test sentence for tokenizer",
+        "another sentence with different words and tokens",
+        "machine learning is fascinating and powerful",
+    ]
+
+    json_path = os.path.join(data_dir, "seq_data.json")
+    with open(json_path, "w", encoding="utf-8") as f:
+        json.dump({"sequence": texts}, f, ensure_ascii=False)
+
+    dataset = DatasetFactory.load(
+        train_type="seq",
+        load_path=data_dir,
+        window_size=16,
+        tokenizer=tokenizer_fn,
+    )
+    assert dataset is not None
+    assert len(dataset) > 0
+    assert dataset.count > 0
+    assert "sequence" in dataset.keys
+
+    item = dataset[0]
+    assert "input_ids" in item
+    assert "target_ids" in item
+    assert item["input_ids"].shape[0] == 16
+
+
+def test_sft_dataset_from_json_text(base_test_env):
+    """Test loading SFT dataset from raw-text JSON with tokenizer"""
+    tokenizer = base_test_env["tokenizer"]
+    tokenizer_fn = _make_tokenizer_fn(tokenizer)
+    test_dir = base_test_env["test_dir"]
+    data_dir = os.path.join(test_dir, "json_sft")
+    os.makedirs(data_dir, exist_ok=True)
+
+    texts = [
+        "user asks a question about the weather",
+        "assistant provides a helpful response to the user",
+    ]
+
+    json_path = os.path.join(data_dir, "sft_data.json")
+    with open(json_path, "w", encoding="utf-8") as f:
+        json.dump(
+            {"sequence": texts, "loss_mask": texts},
+            f,
+            ensure_ascii=False,
+        )
+
+    dataset = DatasetFactory.load(
+        train_type="sft",
+        load_path=data_dir,
+        window_size=16,
+        tokenizer=tokenizer_fn,
+    )
+    assert dataset is not None
+    assert len(dataset) > 0
+
+    item = dataset[0]
+    assert "loss_mask" in item
+
+
+def test_json_storage_explicit_tokenizer(base_test_env):
+    """Test explicit JSON storage with tokenizer"""
+    tokenizer = base_test_env["tokenizer"]
+    tokenizer_fn = _make_tokenizer_fn(tokenizer)
+    test_dir = base_test_env["test_dir"]
+    data_dir = os.path.join(test_dir, "json_explicit")
+    os.makedirs(data_dir, exist_ok=True)
+
+    texts = ["abcdefghijklmnopqrstuvwxyz" * 10]
+
+    json_path = os.path.join(data_dir, "data.json")
+    with open(json_path, "w", encoding="utf-8") as f:
+        json.dump({"sequence": texts}, f, ensure_ascii=False)
+
+    token_count = len(tokenizer_fn(texts[0]))
+
+    dataset = DatasetFactory.load(
+        train_type="seq",
+        load_path=data_dir,
+        window_size=32,
+        storage_type="json",
+        tokenizer=tokenizer_fn,
+    )
+    assert dataset is not None
+    assert len(dataset) > 0
+    assert dataset.count == token_count
+
+
+def test_dataset_count_property(base_test_env):
+    """Test the count property returns correct raw token count"""
+    test_dir = base_test_env["test_dir"]
+
+    seq_length = 200
+    dummy_data = {
+        "sequence": [torch.randint(0, 1000, (seq_length,), dtype=torch.int64)],
+    }
+
+    save_h5(test_dir, "count_test_data", dummy_data)
+
+    dataset = DatasetFactory.load(
+        train_type="seq",
+        load_path=test_dir,
+        window_size=64,
+    )
+
+    assert dataset.count == seq_length
+    assert dataset.count > len(dataset)  # raw tokens > windows
+    assert len(dataset) == (seq_length - 1 - 64) // 64 + 1
+
+
+def test_empty_dataset_count(base_test_env):
+    """Test count returns 0 when no data is loaded"""
+    from astrai.dataset.dataset import SEQDataset
+
+    dataset = SEQDataset(window_size=64, stride=32)
+    assert dataset.count == 0
+    assert dataset.keys == []