diff --git a/debye_bec/bec_widgets/widgets/client.py b/debye_bec/bec_widgets/widgets/client.py
index cb2df5d..c82894c 100644
--- a/debye_bec/bec_widgets/widgets/client.py
+++ b/debye_bec/bec_widgets/widgets/client.py
@@ -13,10 +13,35 @@ logger = bec_logger.logger
 
 
 _Widgets = {
+    "DataViewer": "DataViewer",
     "DigitalTwin": "DigitalTwin",
 }
 
 
+class DataViewer(RPCBase):
+    """Main widget of Data Viewer"""
+
+    _IMPORT_MODULE = "debye_bec.bec_widgets.widgets.data_viewer.data_viewer"
+
+    @rpc_call
+    def remove(self):
+        """
+        Cleanup the BECConnector
+        """
+
+    @rpc_call
+    def attach(self):
+        """
+        None
+        """
+
+    @rpc_call
+    def detach(self):
+        """
+        Detach the widget from its parent dock widget (if widget is in the dock), making it a floating widget.
+        """
+
+
 class DigitalTwin(RPCBase):
     """Main widget of Digital Twin"""
 
diff --git a/debye_bec/bec_widgets/widgets/data_viewer/__init__.py b/debye_bec/bec_widgets/widgets/data_viewer/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/debye_bec/bec_widgets/widgets/data_viewer/data_viewer.py b/debye_bec/bec_widgets/widgets/data_viewer/data_viewer.py
new file mode 100644
index 0000000..9f6ea43
--- /dev/null
+++ b/debye_bec/bec_widgets/widgets/data_viewer/data_viewer.py
@@ -0,0 +1,286 @@
+"""
+Data Viewer: Custom BEC widget to view data from scans.
+"""
+
+import sys
+from datetime import datetime
+from functools import partial
+
+from bec_lib import bec_logger
+from bec_lib.endpoints import MessageEndpoints
+from bec_widgets.utils.bec_dispatcher import BECDispatcher
+from bec_widgets.utils.bec_widget import BECWidget
+from bec_widgets.utils.colors import apply_theme, get_accent_colors
+from bec_widgets.utils.error_popups import SafeSlot
+from qtpy.QtCore import Qt
+
+# pylint: disable=E0611
+from qtpy.QtGui import QFont
+
+# pylint: disable=E0611
+from qtpy.QtWidgets import (
+    QApplication,
+    QComboBox,
+    QDoubleSpinBox,
+    QGroupBox,
+    QHBoxLayout,
+    QLabel,
+    QLayout,
+    QPushButton,
+    QVBoxLayout,
+    QWidget,
+)
+
+from debye_bec.bec_widgets.widgets.data_viewer.qt_widgets import TaggedListWidget
+from debye_bec.bec_widgets.widgets.data_viewer.viewer import HDF5Viewer
+
+logger = bec_logger.logger
+
+
+class DataViewer(BECWidget, QWidget):
+    """
+    Main widget of Data Viewer
+    """
+
+    PLUGIN = True
+    ICON_NAME = "lightbulb"
+
+    def __init__(self, *arg, parent=None, **kwargs):
+        super().__init__(parent=parent, theme_update=True, *arg, **kwargs)
+        self.get_bec_shortcuts()
+
+        central = QWidget()
+        self.root_layout = QVBoxLayout(central)
+
+        self.input = InputPanel()
+        self.viewer = HDF5Viewer()
+
+        self.root_layout.addWidget(self.input, 0)
+        self.root_layout.addWidget(self.viewer, 1)
+
+        self.setLayout(self.root_layout)
+        self.setWindowTitle("Data Viewer")
+        # self.resize(1800, 800)
+
+        self.history = []
+        self.bec_dispatcher.connect_slot(self.on_history_update, MessageEndpoints.scan_history())
+        self.on_history_update()
+
+        self.current_row = 0
+
+        logger.info(self.client.acl)
+        logger.info(self.client.active_account)
+        logger.info(self.client.proc)
+        logger.info(self.client.username)
+
+        self.input.scan_sel.currentItemChanged_connect(self.scan_sel_changed)
+        self.input.load_button.clicked_connect(self.load_dataset)
+        self.input.unload_button.clicked_connect(self.unload_all_datasets)
+
+    @SafeSlot()
+    def scan_sel_changed(self, *_, **kwargs):
+        self.current_row = kwargs["value"]().row()
+
+    @SafeSlot()
+    def load_dataset(
+        self, *_
+    ):  # TODO: Check scan file components for combined xas/xrd scans. Is the Pilatus file in there as well?
+        scan = self.history[self.current_row]
+        file = scan["file_components"][0] + b"_master." + scan["file_components"][1]
+        logger.info(file.decode())
+        self.viewer.load_files([file.decode()])
+
+    @SafeSlot()
+    def unload_all_datasets(self, *_):
+        self.viewer.clear_files()
+
+    def duration_string(self, start: str, end: str) -> str:
+        start_dt = datetime.fromisoformat(start)
+        end_dt = datetime.fromisoformat(end)
+
+        seconds = abs(int((end_dt - start_dt).total_seconds()))
+
+        days, remainder = divmod(seconds, 86400)
+        hours, remainder = divmod(remainder, 3600)
+        minutes, _ = divmod(remainder, 60)
+
+        parts = []
+
+        if days:
+            parts.append(f"{days}d")
+        if hours:
+            parts.append(f"{hours}h")
+        if minutes:
+            parts.append(f"{minutes}min")
+
+        return " ".join(parts) if parts else "<1min"
+
+    @SafeSlot()
+    def on_history_update(self, *_):
+        self.history = []
+        self.input.scan_sel.clear()
+        # Get the length of the scan history, which is 0 when the bec server was started
+        # and no scan has finished yet. Limit the history to the latest 20 scans.
+        max_scans = min(len(self.client.history), 20)
+        for n in range(1, max_scans):  # last scans, up to 20
+            # logger.info(self.client.history[-n].metadata["bec"]["status"])
+            start_time = self.client.history[-n].metadata["start_time"]
+            end_time = self.client.history[-n].metadata["end_time"]
+            logger.info(type(start_time))
+            scan_data = self.client.history[-n].metadata["bec"]
+            # logger.info(scan_data)
+            scan_number = scan_data["scan_number"]
+            scan_name = scan_data["scan_name"]
+            comment = scan_data["metadata"]["user_metadata"]["comment"]
+            sample_name = scan_data["metadata"]["user_metadata"]["sample_name"]
+            status = scan_data["status"]
+            self.history.append(
+                {
+                    "scan_number": scan_number,
+                    "scan_name": scan_name,
+                    "comment": comment,
+                    "sample_name": sample_name,
+                    "file_components": scan_data["file_components"],
+                    "start_time": start_time,
+                    "end_time": end_time,
+                    "status": status,
+                }
+            )
+            tags = []
+            tags.append((scan_name, "#4A90D9"))
+            if sample_name != "":
+                tags.append((sample_name, "#4A10D9"))
+            if comment != "":
+                tags.append((comment, "#FA10D9"))
+            if status == "closed":
+                tags.append((status, "#1F7023"))
+            elif status == "halted":
+                tags.append((status, "#A33047"))
+            else:
+                tags.append((status, "#656365"))
+            tags.append((self.duration_string(start_time, end_time), "#656365"))
+            self.input.scan_sel.addTaggedItem(label=str(scan_number), tags=tags)
+        logger.info(f"Scan history: {self.history}")
+
+
+class InputPanel(QWidget):
+    """Panel for scan selection of the data viewer widget"""
+
+    def __init__(self, parent=None):
+        super().__init__(parent)
+        self._layout = QVBoxLayout(self)
+        self._layout.setSizeConstraint(QLayout.SetFixedSize)  # type: ignore
+
+        # Scan selection
+        self.scan_sel = ListWidget("scan_sel", "Scan", ["Si", "Rh", "Pt"])
+        self.load_button = Button(label_button="Load Dataset", enabled=True)
+        self.unload_button = Button(label_button="Unload all", enabled=True)
+
+        # Assemble complete scan selection group
+        self.input_group = Group(
+            "Scan selection", [self.scan_sel, self.load_button, self.unload_button]
+        )
+
+        self._layout.addWidget(self.input_group)
+        self._layout.addStretch()
+
+
+class Group(QGroupBox):
+    def __init__(self, label, widgets):
+        super().__init__(label)
+        self.layout = QVBoxLayout(self)  # type: ignore
+        for widget in widgets:
+            self.layout.addWidget(widget)  # type: ignore
+
+
+class ListWidget(QWidget):
+    def __init__(self, identifier="", label="", enums=[]):
+        super().__init__()
+        layout = QHBoxLayout(self)
+        layout.setContentsMargins(10, 0, 0, 0)
+        layout.setSpacing(0)
+        self.identifier = identifier
+        # self.label = QLabel(label)
+        # self.label.setFixedWidth(140)
+        # self.label.setContentsMargins(0, 0, 10, 0)
+        # self.label.setWordWrap(True)
+        # layout.addWidget(self.label)
+        self.value = TaggedListWidget()
+        self.value.setFixedWidth(400)
+        # for entry in enums:
+        #     self.value.addItem(entry)
+        layout.addWidget(self.value)
+
+    def clear(self):
+        self.value.clear()
+
+    def addTaggedItem(self, label, tags):
+        self.value.addTaggedItem(label, tags)
+
+    def setCurrentIndex(self, text):
+        self.value.setCurrentIndex(text)
+
+    # def currentIndex(self) -> int:
+    #     return self.value.currentIndex()
+
+    # def has_focus(self) -> bool:
+    #     return QApplication.focusWidget() is self.value.view()
+
+    def currentItemChanged_connect(self, func):
+        """Connect a function to the Enter/Return key press."""
+        self.value.currentItemChanged.connect(
+            partial(
+                func,
+                identifier=self.identifier,
+                value_obj=self.value,
+                value=lambda: self.value.currentIndex(),
+            )
+        )
+
+    def setDisabled(self, disable):
+        self.value.setDisabled(disable)
+
+
+class Button(QWidget):
+    def __init__(self, label=None, label_button: str = "", enabled=False):
+        super().__init__()
+        layout = QHBoxLayout(self)
+        layout.setContentsMargins(10, 0, 0, 0)
+        layout.setSpacing(0)
+        if label is not None:
+            self.label = QLabel(label)
+            self.label.setFixedWidth(140)
+            layout.addWidget(self.label)
+        self.button = QPushButton(label_button)
+        if label is not None:
+            self.button.setFixedWidth(160)
+        self.enable_button(enabled)
+        layout.addWidget(self.button)
+
+    def clicked_connect(self, func):
+        """Connect a function to the button press."""
+        self.button.clicked.connect(func)
+
+    def enable_button(self, enable: bool = False):
+        if enable:
+            self.button.setStyleSheet(
+                f"QPushButton {{background-color: {get_accent_colors().default.name()}; color: white;}}"
+            )
+            self.button.setEnabled(True)
+        else:  # disabled
+            self.button.setStyleSheet(
+                "QPushButton {{background-color: rgb(120, 120, 120); color: white;}}"
+            )
+            self.button.setDisabled(True)
+
+    def setText(self, text):
+        self.button.setText(text)
+
+
+if __name__ == "__main__":
+    app = QApplication(sys.argv)
+    apply_theme("light")
+    dispatcher = BECDispatcher(gui_id="data_viewer")
+    win = DataViewer()
+    win.show()
+    sys.exit(app.exec_())
diff --git a/debye_bec/bec_widgets/widgets/data_viewer/data_viewer.pyproject b/debye_bec/bec_widgets/widgets/data_viewer/data_viewer.pyproject
new file mode 100644
index 0000000..e6d7fe4
--- /dev/null
+++ b/debye_bec/bec_widgets/widgets/data_viewer/data_viewer.pyproject
@@ -0,0 +1 @@
+{'files': ['data_viewer.py']}
\ No newline at end of file
diff --git a/debye_bec/bec_widgets/widgets/data_viewer/data_viewer_plugin.py b/debye_bec/bec_widgets/widgets/data_viewer/data_viewer_plugin.py
new file mode 100644
index 0000000..cf5b92f
--- /dev/null
+++ b/debye_bec/bec_widgets/widgets/data_viewer/data_viewer_plugin.py
@@ -0,0 +1,57 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+from bec_widgets.utils.bec_designer import designer_material_icon
+from qtpy.QtDesigner import QDesignerCustomWidgetInterface
+from qtpy.QtWidgets import QWidget
+
+from debye_bec.bec_widgets.widgets.data_viewer.data_viewer import DataViewer
+
+DOM_XML = """
+<ui language='c++'>
+    <widget class='DataViewer' name='data_viewer'>
+    </widget>
+</ui>
+"""
+
+
+class DataViewerPlugin(QDesignerCustomWidgetInterface):  # pragma: no cover
+    def __init__(self):
+        super().__init__()
+        self._form_editor = None
+
+    def createWidget(self, parent):
+        if parent is None:
+           return QWidget()
+        t = DataViewer(parent)
+        return t
+
+    def domXml(self):
+        return DOM_XML
+
+    def group(self):
+        return ""
+
+    def icon(self):
+        return designer_material_icon(DataViewer.ICON_NAME)
+
+    def includeFile(self):
+        return "data_viewer"
+
+    def initialize(self, form_editor):
+        self._form_editor = form_editor
+
+    def isContainer(self):
+        return False
+
+    def isInitialized(self):
+        return self._form_editor is not None
+
+    def name(self):
+        return "DataViewer"
+
+    def toolTip(self):
+        return "DataViewer"
+
+    def whatsThis(self):
+        return self.toolTip()
diff --git a/debye_bec/bec_widgets/widgets/data_viewer/qt_widgets.py b/debye_bec/bec_widgets/widgets/data_viewer/qt_widgets.py
new file mode 100644
index 0000000..9d7b4f7
--- /dev/null
+++ b/debye_bec/bec_widgets/widgets/data_viewer/qt_widgets.py
@@ -0,0 +1,151 @@
+"""
+TaggedListWidget — a QListWidget where each item shows a label + styled tag pills.
+Selection works natively; no popup, no paintEvent hacks.
+"""
+
+import sys
+
+from qtpy.QtCore import QPoint, QRect, QSize, Qt
+from qtpy.QtGui import QColor, QFont, QFontMetrics, QPainter, QPen
+from qtpy.QtWidgets import (
+    QApplication,
+    QLabel,
+    QListWidget,
+    QListWidgetItem,
+    QStyle,
+    QStyledItemDelegate,
+    QStyleOptionViewItem,
+    QVBoxLayout,
+    QWidget,
+)
+
+# ── Design tokens ──────────────────────────────────────────────────────────────
+ITEM_HEIGHT = 30
+H_PAD = 12
+TAG_H_PAD = 7
+TAG_V_PAD = 3
+TAG_GAP = 5
+LABEL_TAG_GAP = 12
+CORNER_RADIUS = 4
+TAG_TEXT_COLOR = "#FFFFFF"
+
+# ── Enum compat (PySide6 nested vs PyQt5 flat) ────────────────────────────────
+try:
+    _DEMIBOLD = QFont.Weight.DemiBold
+    _MEDIUM = QFont.Weight.Medium
+except AttributeError:
+    _DEMIBOLD = QFont.DemiBold
+    _MEDIUM = QFont.Medium
+
+_AlignVCenter = Qt.AlignmentFlag.AlignVCenter if hasattr(Qt, "AlignmentFlag") else Qt.AlignVCenter
+_AlignCenter = Qt.AlignmentFlag.AlignCenter if hasattr(Qt, "AlignmentFlag") else Qt.AlignCenter
+_UserRole = Qt.ItemDataRole.UserRole if hasattr(Qt, "ItemDataRole") else Qt.UserRole
+_NoPen = Qt.PenStyle.NoPen if hasattr(Qt, "PenStyle") else Qt.NoPen
+_AA = QPainter.RenderHint.Antialiasing if hasattr(QPainter, "RenderHint") else QPainter.Antialiasing
+
+try:
+    _State_Selected = QStyle.StateFlag.State_Selected
+    _State_MouseOver = QStyle.StateFlag.State_MouseOver
+except AttributeError:
+    _State_Selected = QStyle.State_Selected
+    _State_MouseOver = QStyle.State_MouseOver
+
+
+# ── Delegate ──────────────────────────────────────────────────────────────────
+class TaggedDelegate(QStyledItemDelegate):
+
+    def sizeHint(self, option: QStyleOptionViewItem, index) -> QSize:
+        return QSize(option.rect.width() or 300, ITEM_HEIGHT)
+
+    def paint(self, painter: QPainter, option: QStyleOptionViewItem, index) -> None:
+        painter.save()
+
+        is_selected = bool(option.state & _State_Selected)
+        is_hover = bool(option.state & _State_MouseOver)
+
+        # Background
+        if is_selected:
+            painter.fillRect(option.rect, option.palette.highlight())
+        elif is_hover:
+            painter.fillRect(option.rect, QColor("#F1F5F9"))
+        else:
+            painter.fillRect(option.rect, option.palette.base())
+
+        label_text = (
+            index.data(
+                Qt.ItemDataRole.DisplayRole if hasattr(Qt, "ItemDataRole") else Qt.DisplayRole
+            )
+            or ""
+        )
+        tags: list = index.data(_UserRole) or []
+
+        # Label
+        label_font = painter.font()  # inherit default font
+        label_font.setWeight(_DEMIBOLD)
+        painter.setFont(label_font)
+        label_color = (
+            option.palette.highlightedText().color()
+            if is_selected
+            else option.palette.text().color()
+        )
+        painter.setPen(QPen(label_color))
+
+        fm = QFontMetrics(label_font)
+        label_w = fm.horizontalAdvance(label_text)
+        label_y = option.rect.top() + (ITEM_HEIGHT - fm.height()) // 2 + fm.ascent()
+        painter.drawText(QPoint(option.rect.left() + H_PAD, label_y), label_text)
+
+        # Tag pills
+        tag_font = painter.font()  # inherit default font
+        tag_font.setWeight(_MEDIUM)
+        fm_tag = QFontMetrics(tag_font)
+
+        x = option.rect.left() + H_PAD + label_w + LABEL_TAG_GAP
+        for tag_text, hex_color in tags:
+            tag_text = str(tag_text)
+            tw = fm_tag.horizontalAdvance(tag_text) + 2 * TAG_H_PAD
+            th = fm_tag.height() + 2 * TAG_V_PAD
+            ty = option.rect.top() + (ITEM_HEIGHT - th) // 2
+            pill = QRect(x, ty, tw, th)
+
+            fill = QColor(hex_color)
+            if is_selected:
+                fill = fill.lighter(140)
+
+            painter.setRenderHint(_AA)
+            painter.setPen(_NoPen)
+            painter.setBrush(fill)
+            painter.drawRoundedRect(pill, CORNER_RADIUS, CORNER_RADIUS)
+
+            painter.setFont(tag_font)
+            painter.setPen(QPen(QColor(TAG_TEXT_COLOR)))
+            painter.drawText(pill, _AlignCenter, tag_text)
+
+            x += tw + TAG_GAP
+
+        painter.restore()
+
+
+# ── Widget ────────────────────────────────────────────────────────────────────
+class TaggedListWidget(QListWidget):
+    """QListWidget with label + coloured tag pills per row."""
+
+    def __init__(self, parent=None) -> None:
+        super().__init__(parent)
+        self.setItemDelegate(TaggedDelegate(self))
+        self.setMouseTracking(True)  # enables hover highlight
+
+    def addTaggedItem(self, label: str, tags: list | None = None) -> QListWidgetItem:
+        """
+        Add a row.  tags is a list of (text, hex_color) pairs, e.g.
+        [("v1.26", "#2563EB"), ("stable", "#16A34A")]
+        """
+        item = QListWidgetItem(str(label))
+        if tags:
+            item.setData(_UserRole, list(tags))
+        self.addItem(item)
+        return item
+
+    def currentTags(self) -> list:
+        item = self.currentItem()
+        return item.data(_UserRole) or [] if item else []
diff --git a/debye_bec/bec_widgets/widgets/data_viewer/register_data_viewer.py b/debye_bec/bec_widgets/widgets/data_viewer/register_data_viewer.py
new file mode 100644
index 0000000..4ead24d
--- /dev/null
+++ b/debye_bec/bec_widgets/widgets/data_viewer/register_data_viewer.py
@@ -0,0 +1,15 @@
+def main():  # pragma: no cover
+    from qtpy import PYSIDE6
+
+    if not PYSIDE6:
+        print("PYSIDE6 is not available in the environment. Cannot patch designer.")
+        return
+    from PySide6.QtDesigner import QPyDesignerCustomWidgetCollection
+
+    from debye_bec.bec_widgets.widgets.data_viewer.data_viewer_plugin import DataViewerPlugin
+
+    QPyDesignerCustomWidgetCollection.addCustomWidget(DataViewerPlugin())
+
+
+if __name__ == "__main__":  # pragma: no cover
+    main()
diff --git a/debye_bec/bec_widgets/widgets/data_viewer/viewer.py b/debye_bec/bec_widgets/widgets/data_viewer/viewer.py
new file mode 100644
index 0000000..4a99291
--- /dev/null
+++ b/debye_bec/bec_widgets/widgets/data_viewer/viewer.py
@@ -0,0 +1,503 @@
+"""
+HDF5 Viewer — qtpy + pyqtgraph + h5py
+"""
+
+import h5py
+import numpy as np
+import pyqtgraph as pg
+from bec_lib import bec_logger
+from bec_qthemes import material_icon
+from qtpy.QtCore import Qt
+from qtpy.QtGui import QColor, QFont
+from qtpy.QtWidgets import (
+    QAbstractItemView,
+    QGroupBox,
+    QHBoxLayout,
+    QHeaderView,
+    QLabel,
+    QMainWindow,
+    QRadioButton,
+    QSizePolicy,
+    QSlider,
+    QSplitter,
+    QTableWidget,
+    QTableWidgetItem,
+    QTreeWidget,
+    QTreeWidgetItem,
+    QVBoxLayout,
+    QWidget,
+)
+
+logger = bec_logger.logger
+
+# ── Palette ────────────────────────────────────────────────────────────────
+ACCENT = "#7C9CF5"
+TEXT_SEC = "#8A8FA8"
+SUCCESS = "#5FCEA8"
+
+# pyqtgraph color tuples  (R, G, B)
+PG_BG = (28, 30, 38)
+PG_PLOT_BG = (45, 48, 64)
+PG_ACCENT = (124, 156, 245)
+PG_GRID = (58, 61, 80)
+PG_TEXT = (138, 143, 168)
+
+ICON_SIZE = 20
+
+# ── pyqtgraph global config ────────────────────────────────────────────────
+pg.setConfigOptions(
+    background=pg.mkColor(*PG_BG),
+    foreground=pg.mkColor(*PG_TEXT),
+    antialias=True,
+    useOpenGL=False,  # safer default; set True for large datasets if GPU available
+)
+
+
+def _styled_plot_widget(**kwargs) -> pg.PlotWidget:
+    """Return a PlotWidget already themed to match the dark palette."""
+    pw = pg.PlotWidget(**kwargs)
+    # pw.setBackground(pg.mkColor(*PG_PLOT_BG))
+    ax = pw.getPlotItem()
+    for side in ("left", "bottom", "right", "top"):
+        ax.getAxis(side).setPen(pg.mkPen(color=PG_GRID, width=1))
+        ax.getAxis(side).setTextPen(pg.mkPen(color=PG_TEXT))
+    ax.showGrid(x=True, y=True, alpha=0.25)
+    return pw
+
+
+# ── HDF5 Tree helpers ──────────────────────────────────────────────────────
+# TYPE_ICONS = {"group": "📂", "dataset": "📊"}
+
+
+def dtype_tag(ds):
+    d = ds.dtype
+    if np.issubdtype(d, np.integer):
+        return "int"
+    if np.issubdtype(d, np.floating):
+        return "float"
+    if np.issubdtype(d, np.complexfloating):
+        return "complex"
+    if d.kind in ("S", "U", "O"):
+        return "str"
+    return str(d)
+
+
+def populate_tree(parent_item, h5_obj):
+    folder_icon = material_icon("folder", size=(ICON_SIZE, ICON_SIZE), color="#2980b9")
+    vector_icon = material_icon("show_chart", size=(ICON_SIZE, ICON_SIZE), color="#2980b9")
+    array_icon = material_icon("stacked_line_chart", size=(ICON_SIZE, ICON_SIZE), color="#2980b9")
+    scalar_icon = material_icon("point_scan", size=(ICON_SIZE, ICON_SIZE), color="#2980b9")
+    str_icon = material_icon("text_snippet", size=(ICON_SIZE, ICON_SIZE), color="#2980b9")
+
+    if not isinstance(h5_obj, h5py.Group):
+        return
+
+    for key in h5_obj.keys():
+        try:
+            child = h5_obj[key]
+        except Exception:
+            continue
+
+        if isinstance(child, h5py.Group):
+            item = QTreeWidgetItem(parent_item, [key, "Group", ""])
+            item.setIcon(0, folder_icon)
+
+            item.setData(0, Qt.UserRole, child.name)
+            item.setData(0, Qt.UserRole + 1, "group")
+
+            item.setForeground(0, QColor(ACCENT))
+
+            populate_tree(item, child)
+
+        elif isinstance(child, h5py.Dataset):
+            shape_str = "x".join(str(s) for s in child.shape) or "scalar"
+
+            dtype = dtype_tag(child)
+
+            if shape_str == "scalar":
+                if dtype == "str":
+                    icon = str_icon
+                else:
+                    icon = scalar_icon
+            elif "x" in shape_str:
+                icon = array_icon
+            else:
+                icon = vector_icon
+
+            item = QTreeWidgetItem(parent_item, [key, dtype, shape_str])
+            item.setIcon(0, icon)
+
+            item.setData(0, Qt.UserRole, child.name)
+            item.setData(0, Qt.UserRole + 1, "dataset")
+
+            item.setForeground(1, QColor(SUCCESS))
+            item.setForeground(2, QColor(TEXT_SEC))
+
+
+# ── Data / Plot panel ──────────────────────────────────────────────────────
+class DataPanel(QWidget):
+    def __init__(self):
+        super().__init__()
+        self._layout = QVBoxLayout(self)
+
+        # Header
+        hdr = QHBoxLayout()
+        self.path_label = QLabel("Select a dataset from the tree")
+        self.path_label.setObjectName("path_label")
+        self.info_label = QLabel("")
+        self.info_label.setObjectName("info_label")
+        hdr.addWidget(self.path_label, 1)
+        hdr.addWidget(self.info_label)
+        self._layout.addLayout(hdr)
+
+        # View-mode selector
+        mode_box = QGroupBox("View mode")
+        mode_layout = QHBoxLayout(mode_box)
+        mode_layout.setContentsMargins(8, 4, 8, 4)
+        self.rb_auto = QRadioButton("Auto")
+        self.rb_plot = QRadioButton("Plot")
+        self.rb_image = QRadioButton("Image")
+        self.rb_table = QRadioButton("Table")
+        self.rb_auto.setChecked(True)
+        for rb in (self.rb_auto, self.rb_plot, self.rb_image, self.rb_table):
+            mode_layout.addWidget(rb)
+            rb.toggled.connect(self._on_mode_change)
+        mode_layout.addStretch()
+        self._layout.addWidget(mode_box)
+
+        # Content stack
+        self.stack = QWidget()
+        self.stack_layout = QVBoxLayout(self.stack)
+        self.stack_layout.setContentsMargins(0, 0, 0, 0)
+        self._layout.addWidget(self.stack, 1)
+
+        self._current_data = None
+        self._show_empty()
+
+    # ── helpers ───────────────────────────────────────────────────────────
+    def _clear_stack(self):
+        while self.stack_layout.count():
+            item = self.stack_layout.takeAt(0)
+            if item.widget():
+                item.widget().deleteLater()
+
+    def _show_empty(self):
+        self._clear_stack()
+        lbl = QLabel("No data selected")
+        lbl.setObjectName("info_label")
+        lbl.setAlignment(Qt.AlignCenter)
+        self.stack_layout.addWidget(lbl)
+
+    def _on_mode_change(self):
+        if self._current_data is not None:
+            self.display(self._current_data, self.path_label.text())
+
+    def _active_mode(self):
+        if self.rb_plot.isChecked():
+            return "plot"
+        if self.rb_image.isChecked():
+            return "image"
+        if self.rb_table.isChecked():
+            return "table"
+        return "auto"
+
+    # ── public ────────────────────────────────────────────────────────────
+    def display(self, data, path=""):
+        self._current_data = data
+        self.path_label.setText(path)
+
+        if not isinstance(data, np.ndarray):
+            data = np.array(data)
+
+        self.info_label.setText(
+            f"shape {data.shape}  ·  dtype {data.dtype}  ·  {data.size:,} elements"
+        )
+
+        mode = self._active_mode()
+        if mode == "auto":
+            if data.ndim <= 1 and data.size > 1:
+                mode = "plot"
+            elif data.ndim == 2 and min(data.shape) > 1:
+                mode = "image"
+            else:
+                mode = "table"
+
+        if (
+            mode == "plot"
+        ):  # TODO disable plot and image if data is str, maybe completely disable manual mode and only allow image/plot for arrays
+            self._show_plot_1d(data)
+        elif mode == "image":
+            self._show_image_2d(data)
+        else:
+            self._show_table(data)
+
+    # ── 1-D line plot ──────────────────────────────────────────────────────
+    def _show_plot_1d(self, data):
+        self._clear_stack()
+
+        is_2d = data.ndim == 2
+
+        if is_2d:
+            n_rows, n_cols = data.shape
+            row_data = data[0].astype(np.float32)
+        else:
+            row_data = data.reshape(-1).astype(np.float32)
+
+        x = np.arange(row_data.size, dtype=np.float32)
+
+        pw = _styled_plot_widget()
+        pw.setSizePolicy(QSizePolicy.Expanding, QSizePolicy.Expanding)
+
+        plot_item = pw.getPlotItem()
+        plot_item.setAutoVisible(y=False)
+
+        curve = pg.PlotDataItem(
+            x, row_data, pen=pg.mkPen(color=PG_ACCENT, width=1.6), antialias=False
+        )
+        pw.addItem(curve)
+
+        curve.setDownsampling(auto=True, method="peak")
+        curve.setClipToView(True)
+        curve.setSkipFiniteCheck(True)
+
+        # plot_item.setLabel("bottom", "index")
+        # plot_item.setLabel("left", "value")
+        plot_item.enableAutoRange()
+
+        if is_2d:
+            # --- Slider ---
+            slider = QSlider(Qt.Vertical)
+            slider.setMinimum(0)
+            slider.setMaximum(n_rows - 1)
+            slider.setValue(0)
+            # slider.setInvertedAppearance(True)  # row 0 at top
+            slider.setFixedWidth(32)
+            # slider.setSingleStep(1)
+            slider.setPageStep(1)
+
+            row_label = QLabel("0")
+            row_label.setAlignment(Qt.AlignCenter)
+            row_label.setFixedWidth(32)
+            # row_label.setStyleSheet("color: #aaa; font-size: 10px;")
+
+            def on_row_changed(row):
+                row_label.setText(str(row))
+                new_data = data[row].astype(np.float32)
+                new_x = np.arange(new_data.size, dtype=np.float32)
+                curve.setData(new_x, new_data)
+                plot_item.enableAutoRange()
+
+            slider.valueChanged.connect(on_row_changed)
+
+            slider_col = QWidget()
+            slider_col.setFixedWidth(36)
+            col_layout = QVBoxLayout(slider_col)
+            col_layout.setContentsMargins(0, 0, 0, 0)
+            col_layout.setSpacing(2)
+            col_layout.addWidget(row_label)
+            col_layout.addWidget(slider)
+
+            container = QWidget()
+            h_layout = QHBoxLayout(container)
+            h_layout.setContentsMargins(0, 0, 0, 0)
+            h_layout.setSpacing(4)
+            h_layout.addWidget(slider_col)
+            h_layout.addWidget(pw)
+
+            self.stack_layout.addWidget(container)
+        else:
+            self.stack_layout.addWidget(pw)
+
+    # ── 2-D image ──────────────────────────────────────────────────────────
+    def _show_image_2d(self, data):
+        self._clear_stack()
+
+        squeezed = np.squeeze(data)
+        if squeezed.ndim > 2:
+            squeezed = squeezed.reshape(-1, squeezed.shape[-1])
+
+        # complex → magnitude
+        img_data = np.abs(squeezed) if np.iscomplexobj(squeezed) else squeezed.astype(float)
+
+        # ImageView gives us colorbar + histogram + zoom for free
+        iv = pg.ImageView()
+        iv.getView().setBackgroundColor(pg.mkColor(*PG_BG))
+        iv.ui.histogram.setBackground(pg.mkColor(*PG_PLOT_BG))
+        iv.ui.roiBtn.hide()
+        iv.ui.menuBtn.hide()
+
+        # Use 'inferno'-like LUT
+        iv.setColorMap(pg.colormap.get("inferno", source="matplotlib"))
+
+        # pyqtgraph ImageView expects (cols, rows) — transpose so row 0 is at top
+        iv.setImage(img_data.T, autoLevels=True, autoHistogramRange=True)
+        iv.setSizePolicy(QSizePolicy.Expanding, QSizePolicy.Expanding)
+
+        self.stack_layout.addWidget(iv)
+
+    # ── Table ──────────────────────────────────────────────────────────────
+    def _show_table(self, data):
+        self._clear_stack()
+
+        MAX_ROWS, MAX_COLS = 2000, 500
+
+        if data.ndim == 0:
+            flat = data.reshape(1, 1)
+        elif data.ndim == 1:
+            flat = data.reshape(-1, 1)
+        elif data.ndim == 2:
+            flat = data
+        else:
+            flat = data.reshape(-1, data.shape[-1])
+
+        rows, cols = flat.shape
+        show_rows = min(rows, MAX_ROWS)
+        show_cols = min(cols, MAX_COLS)
+
+        if rows > MAX_ROWS or cols > MAX_COLS:
+            note = QLabel(f"⚠  Showing {show_rows}/{rows} rows × {show_cols}/{cols} cols")
+            note.setObjectName("info_label")
+            note.setAlignment(Qt.AlignCenter)
+            self.stack_layout.addWidget(note)
+
+        table = QTableWidget(show_rows, show_cols)
+        table.setEditTriggers(QAbstractItemView.NoEditTriggers)
+        table.setSelectionMode(QAbstractItemView.ContiguousSelection)
+        table.horizontalHeader().setSectionResizeMode(QHeaderView.Interactive)
+        table.horizontalHeader().setDefaultSectionSize(90)
+        table.verticalHeader().setDefaultSectionSize(22)
+        table.setFont(QFont("JetBrains Mono, Consolas, monospace", 10))
+
+        is_float = np.issubdtype(flat.dtype, np.floating)
+        is_complex = np.iscomplexobj(flat)
+        is_bytes = flat.dtype.kind == "S"
+
+        for r in range(show_rows):
+            for c in range(show_cols):
+                val = flat[r, c]
+                txt = (
+                    f"{val:.6g}"
+                    if is_float
+                    else f"{val:.4g}" if is_complex else str(val.decode()) if is_bytes else str(val)
+                )
+                cell = QTableWidgetItem(txt)
+                cell.setTextAlignment(Qt.AlignRight | Qt.AlignVCenter)
+                table.setItem(r, c, cell)
+
+        self.stack_layout.addWidget(table)
+
+
+# ── Main window ────────────────────────────────────────────────────────────
+class HDF5Viewer(QMainWindow):
+    def __init__(self, filepath=None):
+        super().__init__()
+        self.h5files = {}  # filepath -> h5py.File
+        self._build_ui()
+        if filepath:
+            self.load_files([filepath])
+
+    def load_files(self, filepaths: list[str]):
+        """Open one or more HDF5 files and add each as a top-level tree node."""
+        for f in filepaths:
+            if f in self.h5files:
+                continue  # already loaded
+            self.h5files[f] = h5py.File(f, "r")
+            self._add_file_to_tree(f)
+
+    def _build_ui(self):
+        central = QWidget()
+        self.setCentralWidget(central)
+
+        root_layout = QHBoxLayout(central)
+
+        splitter = QSplitter(Qt.Horizontal)
+        splitter.setChildrenCollapsible(False)
+
+        # ── Left pane ──
+        left_pane = QWidget()
+        left_layout = QVBoxLayout(left_pane)
+
+        self.tree = QTreeWidget()
+        self.tree.setHeaderLabels(["Name", "Type", "Shape"])
+        self.tree.header().setStretchLastSection(False)
+        self.tree.header().setSectionResizeMode(0, QHeaderView.Stretch)
+        self.tree.header().setSectionResizeMode(1, QHeaderView.ResizeToContents)
+        self.tree.header().setSectionResizeMode(2, QHeaderView.ResizeToContents)
+        self.tree.itemClicked.connect(self._on_item_clicked)
+
+        left_layout.addWidget(self.tree, 1)
+
+        # ── Right pane ──
+        self.data_panel = DataPanel()
+
+        splitter.addWidget(left_pane)
+        splitter.addWidget(self.data_panel)
+
+        splitter.setStretchFactor(0, 1)
+        splitter.setStretchFactor(1, 3)
+        splitter.setSizes([300, 900])
+        splitter.setHandleWidth(6)
+        splitter.setChildrenCollapsible(False)
+
+        root_layout.addWidget(splitter)
+
+    def _add_file_to_tree(self, filepath: str):
+        """Add a single file as a new top-level node in the tree."""
+        h5file = self.h5files[filepath]
+        filename = filepath.split("/")[-1]
+
+        dataset_icon = material_icon("dataset", size=(ICON_SIZE, ICON_SIZE), color="#2980b9")
+        root_item = QTreeWidgetItem(self.tree, [filename, "Group", ""])
+        root_item.setIcon(0, dataset_icon)
+        root_item.setData(0, Qt.UserRole, "/")
+        root_item.setData(0, Qt.UserRole + 1, "group")
+        root_item.setData(0, Qt.UserRole + 2, filepath)  # so clicks know which file
+        root_item.setForeground(0, QColor(ACCENT))
+
+        populate_tree(root_item, h5file)
+        self.tree.addTopLevelItem(root_item)
+
+        # Expand first 2 levels
+        self.tree.expandItem(root_item)
+        for i in range(root_item.childCount()):
+            self.tree.expandItem(root_item.child(i))
+
+        self.tree.setCurrentItem(root_item)
+
+    def _get_filepath_for_item(self, item: QTreeWidgetItem) -> str:
+        """Walk up the tree to find the filepath stored on the root node."""
+        node = item
+        while node.parent():
+            node = node.parent()
+        return node.data(0, Qt.UserRole + 2)
+
+    def _on_item_clicked(self, item, _col):
+        path = item.data(0, Qt.UserRole)
+        kind = item.data(0, Qt.UserRole + 1)
+        filepath = self._get_filepath_for_item(item)
+
+        if not path or not filepath:
+            return
+
+        h5file = self.h5files[filepath]
+        obj = h5file[path] if path != "/" else h5file
+
+        if kind == "dataset":
+            data = h5file[path][()]
+            self.data_panel.display(data, path)
+        else:
+            n = len(obj) if isinstance(obj, h5py.Group) else 0
+
+    def clear_files(self):
+        """Close all open HDF5 files and reset the tree."""
+        for h5file in self.h5files.values():
+            h5file.close()
+        self.h5files.clear()
+        self.tree.clear()
+        self.data_panel._show_empty()  # TODO: If it works, make function public!
+
+    def closeEvent(self, event):
+        for h5file in self.h5files.values():
+            h5file.close()
+        self.h5files.clear()
+        super().closeEvent(event)
diff --git a/debye_bec/bec_widgets/widgets/designer_plugins.py b/debye_bec/bec_widgets/widgets/designer_plugins.py
index c941b27..5855291 100644
--- a/debye_bec/bec_widgets/widgets/designer_plugins.py
+++ b/debye_bec/bec_widgets/widgets/designer_plugins.py
@@ -5,9 +5,11 @@ from __future__ import annotations
 # pylint: skip-file
 
 designer_plugins = {
+    "DataViewer": ("debye_bec.bec_widgets.widgets.data_viewer.data_viewer", "DataViewer"),
     "DigitalTwin": ("debye_bec.bec_widgets.widgets.digital_twin.digital_twin", "DigitalTwin"),
 }
 
 widget_icons = {
+    "DataViewer": "lightbulb",
     "DigitalTwin": "lightbulb",
 }