diff --git a/client/eepprog.py b/client/eepprog.py
index 58837d0..2a9641f 100755
--- a/client/eepprog.py
+++ b/client/eepprog.py
@@ -1,25 +1,26 @@
 #!/usr/bin/env python3
 
 import click
+import serial.tools.list_ports
 
 from helpers import CliContext, Logger, EepromProgrammer
+from helpers.click import CategorizedGroup
 
 
-@click.group()
+@click.group(cls=CategorizedGroup)
 @click.option('--device', '-d', default='/dev/ttyUSB0', show_default=True,
               metavar='DEVICE', help="Set the serial device")
 @click.option('--baud', '-b', default=38400, show_default=True,
               metavar='BAUDRATE', help="Set the baud rate of the serial device")
 @click.option('--verbose', '-v', is_flag=True, help='Print debug output')
 @click.pass_context
-def eepprog(ctx: click.Context, device: str, baud: int, verbose: bool):
+def eepprog(ctx: click.Context, device: str, baud: int, verbose: bool) -> None:
     # Create dependencies
     logger = Logger(verbose=verbose)
     eeprom_programmer = EepromProgrammer(logger=logger, device=device, baudrate=baud)
 
-    logger.debug("Creating CLI context (device: {}, bauds: {})".format(device, baud))
-
     # Create CLI context
+    logger.debug("Creating CLI context")
     ctx.obj = CliContext(
         logger=logger,
         eeprom_programmer=eeprom_programmer,
@@ -29,9 +30,9 @@ def eepprog(ctx: click.Context, device: str, baud: int, verbose: bool):
     ctx.call_on_close(eeprom_programmer.close)
 
 
-@eepprog.command('hello', short_help='Say hello. :)')
+@eepprog.command('hello', category='Test commands', short_help='Say hello. :)')
 @click.pass_obj
-def hello(context: CliContext):
+def hello(context: CliContext) -> None:
     """
     Say hello. :)
 
@@ -46,19 +47,36 @@ def hello(context: CliContext):
     context.logger.success('yay!')
 
 
-@eepprog.command('test', short_help="Send INIT command to the programmer and read answer")
+@eepprog.command('test', category='Test commands', short_help="Send INIT command to the programmer and read answer")
 @click.pass_obj
-def test(context: CliContext):
+def test(context: CliContext) -> None:
     """
     Send an 'INIT' command to the programmer and read the answer.
 
     Test command for debugging.
     """
-    context.eeprom_programmer.test()
+    context.eeprom_programmer.test_command()
+
+
+@eepprog.command('list-devices', category='Helper commands', short_help="List available serial ports")
+@click.pass_obj
+def list_devices(context: CliContext) -> None:
+    """
+    List serial ports that are available on the system.
+
+    Internally uses 'serial.tools.list_ports' of pySerial.
+    """
+    context.logger.debug("Getting list of serial ports")
+    ports = serial.tools.list_ports.comports()
+
+    context.logger.debug()  # Print empty line
+    click.echo("Found {} serial ports:".format(len(ports)))
+    for port in ports:
+        click.echo('' + str(port))
+
 
-# TODO command: list-devices -> serial.tools.list_ports
 # TODO shell: Run an interactive shell
 
 
 if __name__ == '__main__':
-    eepprog()
+    eepprog(max_content_width=120)
diff --git a/client/helpers/EepromProgrammer.py b/client/helpers/EepromProgrammer.py
index d529ddc..19f55ec 100644
--- a/client/helpers/EepromProgrammer.py
+++ b/client/helpers/EepromProgrammer.py
@@ -1,5 +1,5 @@
 from serial import Serial
-from typing import Optional
+from typing import Optional, Union
 
 from . import Logger
 
@@ -20,33 +20,49 @@ class EepromProgrammer:
         self._device_file = device
         self._baudrate = baudrate
 
-    # TODO
-    def open(self):
+    def open(self) -> None:
         """
         Open and setup serial port.
         """
         assert self.serial is None, 'Serial port is already opened!'
 
-        self.logger.debug("Setting up serial device '{}' with baudrate {}".format(self._device_file, self._baudrate))
+        self.logger.debug("Opening serial device '{}' with {} bauds".format(self._device_file, self._baudrate))
         self.serial = Serial(self._device_file, self._baudrate)
 
-    def close(self):
-        if self.serial is None:
-            self.logger.debug("Serial port is already closed")
-            return
+    def close(self) -> None:
+        """
+        Closes the serial port.
+        """
+        if self.serial is not None:
+            self.logger.debug("Closing serial port")
+            self.serial.close()
 
-        self.logger.debug("Closing serial port")
-        self.serial.close()
+    def write(self, data: Union[bytes, bytearray]) -> int:
+        """
+        Writes bytes to the serial port and writes debug log.
+        """
+        self.logger.debug('Writing: {}'.format(str(data)))
+        return self.serial.write(data)
 
     # TODO
-    def test(self):
+    def test_command(self) -> None:
         # Open serial port
         if self.serial is None:
             self.open()
 
+        # TODO where to do this? in open() or when needed?
+        self.serial.timeout = 1
+
         # Write a test command
-        self.logger.info("Sending 'INIT' ...")
-        self.serial.write(b"INIT\n")
+        self.logger.info("Sending INIT command ...")
+        self.write(b'INIT BINARY\n')
 
         # Just read some stuff
-        self.logger.info("Read line: ", self.serial.readline(80))
+        self.logger.info("Received line: ", self.serial.readline(80))
+
+        # Send a READ command
+        self.logger.info("Sending READ command ...")
+        self.write(b'READ 0000:0010\n')
+
+        while True:
+            self.logger.info("Received line: ", self.serial.readline(80))
diff --git a/client/helpers/click.py b/client/helpers/click.py
new file mode 100644
index 0000000..ff38a6a
--- /dev/null
+++ b/client/helpers/click.py
@@ -0,0 +1,69 @@
+import click
+import collections
+
+
+class CategorizedGroup(click.Group):
+    """
+    Click command group that categorizes subcommands in the help text by the additional 'category' attribute.
+    Commands that don't have a 'category' attribute are grouped under the default category "Commands" as usual.
+
+    Example usage:
+    `@categorized_group.command('foobar', category='Debug commands')`
+    """
+    default_category: str
+
+    def __init__(self, name=None, commands=None, default_category: str = 'Commands', **attrs):
+        super().__init__(name, commands, **attrs)
+        self.commands = commands or collections.OrderedDict()
+        self.default_category = default_category
+
+    def list_commands(self, ctx):
+        """ List commands in the order they were added to the group. """
+        return self.commands
+
+    def command(self, *args, **kwargs):
+        """ Extends the command decorator by setting a category attribute on the command. """
+        category = kwargs.pop('category', None)
+        orig_decorator = super().command(*args, **kwargs)
+
+        def decorator(f):
+            cmd = orig_decorator(f)
+            if category:
+                cmd.category = category
+            return cmd
+
+        return decorator
+
+    def format_commands(self, ctx, formatter):
+        """
+        Prints commands in help messages.
+        This version groups them into categories and is based on the original Group.format_commands method.
+        """
+        categorized_commands = {self.default_category: []}
+
+        # Collect subcommands grouped by category
+        for subcommand in self.list_commands(ctx):
+            cmd = self.get_command(ctx, subcommand)
+            if cmd is None or cmd.hidden:
+                continue
+
+            category = getattr(cmd, 'category', self.default_category)
+            if categorized_commands.get(category) is None:
+                categorized_commands[category] = []
+
+            categorized_commands[category].append((subcommand, cmd))
+
+        # Print help sections for each subcommand category
+        for category, subcommands in categorized_commands.items():
+            if not len(subcommands):
+                continue
+
+            limit = formatter.width - 6 - max(len(cmd[0]) for cmd in subcommands)
+
+            rows = []
+            for subcommand, cmd in subcommands:
+                help_str = cmd.get_short_help_str(limit)
+                rows.append((subcommand, help_str))
+
+            with formatter.section(category):
+                formatter.write_dl(rows)