diff --git a/src/server/communication/message_data.py b/src/server/communication/message_data.py
index c11bb52..445840d 100644
--- a/src/server/communication/message_data.py
+++ b/src/server/communication/message_data.py
@@ -2,6 +2,8 @@
 import csv
 from dataclasses import dataclass
 
+import numpy as np
+
 from server.logger.log import logger
 
 
@@ -9,20 +11,20 @@
 class MessageData:
     topic: str
     payload: str
-    device_id: int
-    message_id: int
-    message_content: str
-    timestamp: str
+    device_id: str
+    message_id: str
+    message_content: dict
+    timestamp: float
 
-    received_timestamp = None
-    avg_speed = None
-    latency = None
-    synthetic_latency = None
-    payload_size = None
-    offloading_layer_index = None
-    layer_output = None
-    device_layers_inference_time = None
-    device_cpu_percent = None
+    received_timestamp: float | None = None
+    avg_speed: float | None = None
+    latency: float | None = None
+    synthetic_latency: float | None = None
+    payload_size: int | None = None
+    offloading_layer_index: int | None = None
+    layer_output: np.ndarray | None = None
+    device_layers_inference_time: np.ndarray | None = None
+    device_cpu_percent: float | None = None
 
     def to_dict(self):
         return self.__dict__
diff --git a/tests/unit/test_message_data.py b/tests/unit/test_message_data.py
index ab73ef0..2afcd47 100644
--- a/tests/unit/test_message_data.py
+++ b/tests/unit/test_message_data.py
@@ -1,8 +1,50 @@
+import dataclasses
 from typing import get_type_hints
 
 from server.communication.message_data import MessageData
 
 
+def test_core_field_annotations_match_runtime_types():
+    annotations = get_type_hints(MessageData)
+
+    assert annotations["device_id"] is str
+    assert annotations["message_id"] is str
+    assert annotations["message_content"] is dict
+    assert annotations["timestamp"] is float
+
+
+def test_dynamically_populated_attributes_are_real_dataclass_fields():
+    field_names = {f.name for f in dataclasses.fields(MessageData)}
+
+    for attribute in (
+        "received_timestamp",
+        "avg_speed",
+        "latency",
+        "synthetic_latency",
+        "payload_size",
+        "offloading_layer_index",
+        "layer_output",
+        "device_layers_inference_time",
+        "device_cpu_percent",
+    ):
+        assert attribute in field_names, f"{attribute} is not a dataclass field"
+
+
+def test_optional_fields_default_to_none():
+    message_data = MessageData(
+        topic="topic",
+        payload="",
+        device_id="device-1",
+        message_id="msg-1",
+        message_content={},
+        timestamp=123.456,
+    )
+
+    assert message_data.received_timestamp is None
+    assert message_data.avg_speed is None
+    assert message_data.device_cpu_percent is None
+
+
 def test_get_latency_returns_duration_as_float():
     latency = MessageData.get_latency("10.5", "12.75")