diff --git a/doc/source/script_reference.rst b/doc/source/script_reference.rst
index 37b8cbb..cf90b85 100644
--- a/doc/source/script_reference.rst
+++ b/doc/source/script_reference.rst
@@ -11,6 +11,16 @@ checkGenuine.py
    :func: get_argparser
    :prog: python -m ledgerblue.checkGenuine
 
+.. _debugApp.py:
+
+debugApp.py
+-----------
+
+.. argparse::
+   :module: ledgerblue.debugApp
+   :func: get_argparser
+   :prog: python -m ledgerblue.debugApp
+
 .. _deleteApp.py:
 
 deleteApp.py
diff --git a/ledgerblue/debugApp.py b/ledgerblue/debugApp.py
new file mode 100644
index 0000000..4f0a9a7
--- /dev/null
+++ b/ledgerblue/debugApp.py
@@ -0,0 +1,146 @@
+"""
+*******************************************************************************
+*   Ledger Blue
+*   (c) 2016 Ledger
+*
+*  Licensed under the Apache License, Version 2.0 (the "License");
+*  you may not use this file except in compliance with the License.
+*  You may obtain a copy of the License at
+*
+*      http://www.apache.org/licenses/LICENSE-2.0
+*
+*  Unless required by applicable law or agreed to in writing, software
+*  distributed under the License is distributed on an "AS IS" BASIS,
+*  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+*  See the License for the specific language governing permissions and
+*  limitations under the License.
+********************************************************************************
+"""
+
+import argparse
+import sys
+import time
+from datetime import datetime
+
+import serial
+import serial.tools.list_ports
+
+LEDGER_VENDOR_ID = 0x2C97
+
+
+def get_argparser():
+    parser = argparse.ArgumentParser(
+        description="Listen to debug output from a Ledger app compiled with DEBUG_OVER_USB."
+    )
+    parser.add_argument(
+        "--port", "-p",
+        help="Serial port to use (e.g. COM3 on Windows, /dev/ttyACM0 on Linux). Auto-detected if omitted.",
+        type=str,
+        default=None,
+    )
+    parser.add_argument(
+        "--baudrate", "-b",
+        help="Baud rate for the serial connection (default: 115200).",
+        type=int,
+        default=115200,
+    )
+    parser.add_argument(
+        "--output", "-o",
+        help="Write debug output to a file in addition to stdout.",
+        type=str,
+        default=None,
+    )
+    return parser
+
+
+def find_ledger_cdc_port(port=None):
+    """Find the Ledger device's CDC (virtual serial) port.
+
+    When DEBUG_OVER_USB is enabled in a Ledger app, the device exposes
+    an additional USB CDC interface that sends PRINTF debug output.
+    """
+    if port:
+        return port
+
+    for p in serial.tools.list_ports.comports():
+        if p.vid == LEDGER_VENDOR_ID:
+            return p.device
+
+    return None
+
+
+def wait_for_cdc_port(port=None, timeout=0):
+    """Wait for the Ledger CDC port to appear.
+
+    If timeout is 0, wait indefinitely.
+    Returns the port name, or None if timeout expired.
+    """
+    start = time.time()
+    first = True
+    while True:
+        cdc_port = find_ledger_cdc_port(port)
+        if cdc_port is not None:
+            if not first:
+                sys.stdout.write("\n")
+                sys.stdout.flush()
+            return cdc_port
+        if first:
+            print("Waiting for Ledger CDC debug port...", end="", flush=True)
+            first = False
+        else:
+            sys.stdout.write(".")
+            sys.stdout.flush()
+        if timeout and (time.time() - start) >= timeout:
+            sys.stdout.write("\n")
+            sys.stdout.flush()
+            return None
+        time.sleep(1)
+
+
+if __name__ == "__main__":
+    args = get_argparser().parse_args()
+
+    output_file = None
+    if args.output:
+        try:
+            output_file = open(args.output, "a", encoding="utf-8")
+        except OSError:
+            print("Unable to open file {} for writing.".format(args.output))
+            sys.exit(1)
+
+    try:
+        while True:
+            cdc_port = wait_for_cdc_port(args.port)
+            if cdc_port is None:
+                print(
+                    "No Ledger CDC debug port found.\n"
+                    "Make sure your Ledger app was compiled with DEBUG_OVER_USB=1\n"
+                    "and that the device is connected and the app is running.\n"
+                    "You can also specify the port manually with --port."
+                )
+                sys.exit(1)
+
+            print("Connected on {} (baudrate={}).".format(cdc_port, args.baudrate))
+            print("Press Ctrl+C to stop.\n")
+
+            try:
+                with serial.Serial(cdc_port, args.baudrate, timeout=1) as ser:
+                    while True:
+                        data = ser.readline()
+                        if data:
+                            text = data.decode("utf-8", errors="replace")
+                            timestamp = datetime.now().strftime("%H:%M:%S.%f")[:-3]
+                            for line in text.splitlines(True):
+                                stamped = "[{}] {}".format(timestamp, line)
+                                sys.stdout.write(stamped)
+                                sys.stdout.flush()
+                                if output_file:
+                                    output_file.write(stamped)
+                                    output_file.flush()
+            except serial.SerialException:
+                print("\nSerial connection lost. Waiting for device...")
+    except KeyboardInterrupt:
+        print("\nStopped.")
+    finally:
+        if output_file:
+            output_file.close()
diff --git a/pyproject.toml b/pyproject.toml
index 1badc33..2d02f46 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -43,7 +43,8 @@ dependencies = [
     "nfcpy>=1.0.4",
     "bleak>=0.20.1",
     "pycryptodome>=3.18.0",
-    "python-gnupg>=0.5.0"
+    "python-gnupg>=0.5.0",
+    "pyserial>=3.5"
 ]
 
 [tool.setuptools]