diff --git a/diagnostic_common_diagnostics/diagnostic_common_diagnostics/hd_monitor.py b/diagnostic_common_diagnostics/diagnostic_common_diagnostics/hd_monitor.py
index 93a9f6ac..2eecf3dc 100755
--- a/diagnostic_common_diagnostics/diagnostic_common_diagnostics/hd_monitor.py
+++ b/diagnostic_common_diagnostics/diagnostic_common_diagnostics/hd_monitor.py
@@ -1,4 +1,5 @@
 #! /usr/bin/env python3
+"""Hard Drive (or any other memory) monitor. Contains a the monitor node and its main function."""
 # -*- coding: utf-8 -*-
 #
 # Software License Agreement (BSD License)
@@ -36,60 +37,78 @@
 # \author Kevin Watts
 # \author Antoine Lima
 
-from typing import List
 from pathlib import Path
-from socket import gethostname
 from shutil import disk_usage
+from socket import gethostname
+from typing import List
 
-import rclpy
+from diagnostic_msgs.msg import DiagnosticStatus, KeyValue
+from diagnostic_updater import Updater
 from rcl_interfaces.msg import SetParametersResult
+import rclpy
 from rclpy.node import Node
-from diagnostic_updater import Updater
-from diagnostic_msgs.msg import DiagnosticStatus, KeyValue
 
 
 FREE_PERCENT_LOW = 0.05
 FREE_PERCENT_CRIT = 0.01
 DICT_STATUS = {
-    DiagnosticStatus.OK: "OK",
-    DiagnosticStatus.WARN: "Warning",
-    DiagnosticStatus.ERROR: "Error",
+    DiagnosticStatus.OK: 'OK',
+    DiagnosticStatus.WARN: 'Warning',
+    DiagnosticStatus.ERROR: 'Error',
 }
 DICT_USAGE = {
-    DiagnosticStatus.OK: "OK",
-    DiagnosticStatus.WARN: "Low Disk Space",
-    DiagnosticStatus.ERROR: "Very Low Disk Space",
+    DiagnosticStatus.OK: 'OK',
+    DiagnosticStatus.WARN: 'Low Disk Space',
+    DiagnosticStatus.ERROR: 'Very Low Disk Space',
 }
 
 
 class HDMonitor(Node):
+    """Diagnostic node checking the remaining space on the specified hard drive.
+
+    Three ROS parameters:
+    - path: Path on the filesystem to check (string, default: home directory)
+    - free_percent_low: Percentage at which to consider the space left as low
+    - free_percent_crit: Percentage at which to consider the space left as critical
+    """
+
     def __init__(self):
-        hostname = gethostname().replace(".", "_").replace("-", "_")
-        super().__init__(f"hd_monitor_{hostname}")
+        hostname = gethostname().replace('.', '_').replace('-', '_')
+        super().__init__(f'hd_monitor_{hostname}')
 
         self.add_on_set_parameters_callback(self.callback_config)
-        self.declare_parameter("path", "~")
-        self.declare_parameter("free_percent_low", 0.05)
-        self.declare_parameter("free_percent_crit", 0.01)
+        self.declare_parameter('path', '~')
+        self.declare_parameter('free_percent_low', 0.05)
+        self.declare_parameter('free_percent_crit', 0.01)
+        self._path = self._free_percent_low = self._free_percent_crit = None
 
         self._updater = Updater(self)
         self._updater.setHardwareID(hostname)
-        self._updater.add(f"{hostname} HD Usage", self.check_disk_usage)
+        self._updater.add(f'{hostname} HD Usage', self.check_disk_usage)
 
     def callback_config(self, params: List[rclpy.Parameter]):
+        """Retrieve ROS parameters.
+
+        see the class documentation for declared parameters.
+        """
         for param in params:
             match param.name:
-                case "path":
+                case 'path':
                     self._path = str(
                         Path(param.value).expanduser().resolve(strict=True)
                     )
-                case "free_percent_low":
+                case 'free_percent_low':
                     self._free_percent_low = param.value
-                case "free_percent_crit":
+                case 'free_percent_crit':
                     self._free_percent_crit = param.value
+
         return SetParametersResult(successful=True)
 
     def check_disk_usage(self, diag: DiagnosticStatus) -> DiagnosticStatus:
+        """Compute the disk usage and derive a status from it.
+
+        Task periodically ran by the diagnostic updater.
+        """
         diag.level = DiagnosticStatus.OK
 
         total, _, free = disk_usage(self._path)
@@ -102,13 +121,13 @@ def check_disk_usage(self, diag: DiagnosticStatus) -> DiagnosticStatus:
         else:
             diag.level = DiagnosticStatus.ERROR
 
-        total_Go = total // (1024 * 1024)
+        total_go = total // (1024 * 1024)
         diag.values.extend(
             [
-                KeyValue(key="Name", value=self._path),
-                KeyValue(key="Status", value=DICT_STATUS[diag.level]),
-                KeyValue(key="Total (Go)", value=str(total_Go)),
-                KeyValue(key="Available (%)", value=str(round(percent, 2))),
+                KeyValue(key='Name', value=self._path),
+                KeyValue(key='Status', value=DICT_STATUS[diag.level]),
+                KeyValue(key='Total (Go)', value=str(total_go)),
+                KeyValue(key='Available (%)', value=str(round(percent, 2))),
             ]
         )
 
@@ -117,6 +136,7 @@ def check_disk_usage(self, diag: DiagnosticStatus) -> DiagnosticStatus:
 
 
 def main(args=None):
+    """Run the HDMonitor class."""
     rclpy.init(args=args)
 
     node = HDMonitor()
@@ -126,5 +146,5 @@ def main(args=None):
         pass
 
 
-if __name__ == "__main__":
+if __name__ == '__main__':
     main()