diff --git a/platformio.ini b/platformio.ini
index f02579d..9e57f2e 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -11,11 +11,12 @@ build_flags =
 lib_deps =
     fastled/FastLED@^3
     h2zero/NimBLE-Arduino@^2
-upload_port = /dev/serial/by-id/usb-Espressif_USB_JTAG_serial_debug_unit_44:1B:F6:F4:CF:14-if00
 upload_speed = 115200
 upload_flags = --no-stub
 build_src_filter = +<main.cpp> -<client.cpp>
-extra_scripts = pre:tools/pio_version_pre.py
+extra_scripts =
+    pre:tools/pio_version_pre.py
+    post:tools/pio_upload_port.py
 
 [env:s3lite-client]
 platform = espressif32@6.7.0
@@ -31,8 +32,9 @@ build_flags =
 lib_deps =
     fastled/FastLED@^3
     h2zero/NimBLE-Arduino@^2
-upload_port = /dev/ttyACM2
 upload_speed = 115200
 upload_flags = --no-stub
 build_src_filter = +<client.cpp> -<main.cpp>
-extra_scripts = pre:tools/pio_version_pre.py
+extra_scripts =
+    pre:tools/pio_version_pre.py
+    post:tools/pio_upload_port.py
diff --git a/src/client.cpp b/src/client.cpp
index 0dc079c..dfed816 100644
--- a/src/client.cpp
+++ b/src/client.cpp
@@ -263,6 +263,8 @@ void loop() {
                 } else {
                     Serial.println("NO_KEY");
                 }
+            } else if (serialBuf == "ID?") {
+                Serial.println("SylDa_Client");
             } else if (serialBuf == "VERSION?") {
                 Serial.print("BUILD_NR:");
                 Serial.println(FIRMWARE_VERSION_CLIENT);
diff --git a/src/main.cpp b/src/main.cpp
index e12cbd5..473712c 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -485,6 +485,8 @@ void loop() {
                 } else {
                     Serial.println("NO_KEY");
                 }
+            } else if (serialBuf == "ID?") {
+                Serial.println("SylDa_Server");
             } else if (serialBuf == "VERSION?") {
                 Serial.print("BUILD_NR:");
                 Serial.println(FIRMWARE_VERSION);
diff --git a/tools/pio_upload_port.py b/tools/pio_upload_port.py
new file mode 100644
index 0000000..cd66b77
--- /dev/null
+++ b/tools/pio_upload_port.py
@@ -0,0 +1,118 @@
+#!/usr/bin/env python3
+"""POST-script: auto-detect upload_port by querying connected ESP32s.
+
+Each ESP32 running SylDa firmware responds to the serial command "ID?"
+with either "SylDa_Server" or "SylDa_Client". This script scans
+/dev/serial/by-id/ for Espressif devices, queries each one, and sets
+UPLOAD_PORT for the matching environment.
+
+If no device responds (e.g. first flash), the user is prompted to
+select a port manually.
+"""
+Import("env")
+
+if env.IsIntegrationDump():
+    Return()
+
+ENV_TO_ID = {
+    "s3lite-server": "SylDa_Server",
+    "s3lite-client": "SylDa_Client",
+}
+
+import glob
+import os
+import sys
+import time
+
+try:
+    import serial
+except ImportError:
+    print("  WARNING: pyserial not installed, skipping auto-detect")
+    print("  Install: pip install pyserial")
+    Return()
+
+
+def find_esp32_ports():
+    by_id = "/dev/serial/by-id"
+    if not os.path.isdir(by_id):
+        return []
+    ports = []
+    for entry in sorted(os.listdir(by_id)):
+        if "Espressif" in entry or "espressif" in entry:
+            ports.append(os.path.join(by_id, entry))
+    return ports
+
+
+def query_id(port, timeout=5):
+    try:
+        ser = serial.Serial(port, 115200, timeout=0.5)
+        time.sleep(0.1)
+        ser.reset_input_buffer()
+        ser.write(b"ID?\n")
+        deadline = time.time() + timeout
+        while time.time() < deadline:
+            line = ser.readline().decode("utf-8", errors="ignore").strip()
+            if line:
+                ser.close()
+                return line
+        ser.close()
+    except (serial.SerialException, OSError):
+        pass
+    return None
+
+
+def detect_port(source, target, env):
+    env_name = env.subst("$PIOENV")
+    expected_id = ENV_TO_ID.get(env_name)
+
+    if not expected_id:
+        print(f"  Unknown environment '{env_name}', skipping auto-detect")
+        return
+
+    ports = find_esp32_ports()
+
+    if not ports:
+        print(f"  No ESP32 serial ports found in /dev/serial/by-id/")
+        print(f"  Connect an ESP32 and try again")
+        sys.exit(1)
+
+    if len(ports) == 1:
+        port = ports[0]
+        resp = query_id(port, timeout=5)
+        if resp and expected_id in resp:
+            print(f"  Auto-detected {expected_id} on {port}")
+        else:
+            if resp:
+                print(f"  Found '{resp}' on {port} (expected {expected_id})")
+            print(f"  Only one ESP32 connected, using {port}")
+        env["UPLOAD_PORT"] = port
+        return
+
+    for port in ports:
+        resp = query_id(port, timeout=5)
+        if resp and expected_id in resp:
+            print(f"  Found {expected_id} on {port}")
+            env["UPLOAD_PORT"] = port
+            return
+
+    print(f"\n  Cannot auto-detect {expected_id} (no ID? response matched)")
+    print(f"  Available ESP32 ports:")
+    for i, port in enumerate(ports, 1):
+        resp = query_id(port, timeout=3)
+        label = f" ({resp})" if resp else ""
+        print(f"    {i}: {port}{label}")
+
+    try:
+        choice = input(f"  Select port for {env_name} [{expected_id}] (1-{len(ports)}): ")
+        idx = int(choice) - 1
+        if 0 <= idx < len(ports):
+            env["UPLOAD_PORT"] = ports[idx]
+            return
+    except (ValueError, EOFError):
+        pass
+
+    print("  Invalid choice, aborting upload")
+    sys.exit(1)
+
+
+env.AddPreAction("upload", detect_port)