diff --git a/bec_widgets/validation/monitor_config_validator.py b/bec_widgets/validation/monitor_config_validator.py
index 84008928..27cdc212 100644
--- a/bec_widgets/validation/monitor_config_validator.py
+++ b/bec_widgets/validation/monitor_config_validator.py
@@ -60,7 +60,7 @@ class Signal(BaseModel):
         if entry not in device.signals:
             raise PydanticCustomError(
                 "no_entry_for_device",
-                "Entry '{wrong_value}' not found in device '{device_name}' signals",
+                'Entry "{wrong_value}" not found in device "{device_name}" signals',
                 {"wrong_value": entry, "device_name": name},
             )
 
@@ -100,8 +100,8 @@ class PlotConfig(BaseModel):
     def validate_x_signals(cls, v):
         if len(v.signals) != 1:
             raise PydanticCustomError(
-                "x_device_one_signal",
-                "There must be exactly one signal for x axis. Number of x signals: '{wrong_value}'",
+                "x_axis_multiple_signals",
+                'There must be exactly one signal for x axis. Number of x signals: "{wrong_value}"',
                 {"wrong_value": v},
             )
 
diff --git a/tests/test_bec_monitor.py b/tests/test_bec_monitor.py
index 6e9f9b00..54577690 100644
--- a/tests/test_bec_monitor.py
+++ b/tests/test_bec_monitor.py
@@ -54,6 +54,11 @@ def mocked_client():
     device_names = ["samx", "gauss_bpm", "gauss_adc1", "gauss_adc2", "gauss_adc3", "bpm4i"]
     mocked_devices = {name: get_mocked_device(name) for name in device_names}
 
+    # Adding a device with empty signals for validation tests
+    no_signal_device = FakeDevice(name="no_signal_device")
+    del no_signal_device.signals  # Simulate a device with no signals
+    mocked_devices["no_signal_device"] = no_signal_device
+
     # Create a MagicMock object
     client = MagicMock()
 
diff --git a/tests/test_validator_errors.py b/tests/test_validator_errors.py
new file mode 100644
index 00000000..7657b9cf
--- /dev/null
+++ b/tests/test_validator_errors.py
@@ -0,0 +1,80 @@
+# pylint: disable=missing-function-docstring
+import pytest
+from pydantic import ValidationError
+from bec_widgets.validation.monitor_config_validator import (
+    MonitorConfigValidator,
+    Signal,
+    PlotAxis,
+    PlotConfig,
+)
+
+from test_bec_monitor import mocked_client
+
+
+@pytest.fixture(scope="function")
+def setup_devices(mocked_client):
+    MonitorConfigValidator.devices = mocked_client.device_manager.devices
+
+
+def test_signal_validation_name_missing(setup_devices):
+    with pytest.raises(ValidationError) as excinfo:
+        Signal(name=None)
+    errors = excinfo.value.errors()
+    assert len(errors) == 1
+    assert errors[0]["type"] == "no_device_name"
+    assert "Device name must be provided" in str(excinfo.value)
+
+
+def test_signal_validation_name_not_in_bec(setup_devices):
+    with pytest.raises(ValidationError) as excinfo:
+        Signal(name="non_existent_device")
+    errors = excinfo.value.errors()
+    assert len(errors) == 1
+    assert errors[0]["type"] == "no_device_bec"
+    assert 'Device "non_existent_device" not found in current BEC session' in str(excinfo.value)
+
+
+def test_signal_validation_device_has_no_signals(setup_devices):
+    with pytest.raises(ValidationError) as excinfo:
+        Signal(name="no_signal_device")
+
+    errors = excinfo.value.errors()
+    assert len(errors) == 1
+    assert errors[0]["type"] == "no_device_signals"
+    assert 'Device "no_signal_device" does not have "signals" defined' in errors[0]["msg"]
+
+
+def test_signal_validation_entry_not_in_device(setup_devices):
+    with pytest.raises(ValidationError) as excinfo:
+        Signal(name="samx", entry="non_existent_entry")
+
+    errors = excinfo.value.errors()
+    assert len(errors) == 1
+    assert errors[0]["type"] == "no_entry_for_device"
+    assert 'Entry "non_existent_entry" not found in device "samx" signals' in errors[0]["msg"]
+
+
+def test_signal_validation_success(setup_devices):
+    signal = Signal(name="samx")
+    assert signal.name == "samx"
+
+
+def test_plot_config_x_axis_signal_validation(setup_devices):
+    # Setup a valid signal
+    valid_signal = Signal(name="samx")
+
+    # Case with more than one signal for x-axis
+    plot_axis_multiple_signals = PlotAxis(
+        signals=[valid_signal, valid_signal], label="X Axis Label"
+    )
+    with pytest.raises(ValidationError) as excinfo:
+        PlotConfig(
+            plot_name="Test Plot",
+            x=plot_axis_multiple_signals,
+            y=PlotAxis(signals=[valid_signal], label="Y Axis Label"),
+        )
+
+    errors = excinfo.value.errors()
+    assert len(errors) == 1
+    assert errors[0]["type"] == "x_axis_multiple_signals"
+    assert "There must be exactly one signal for x axis" in errors[0]["msg"]