diff --git a/common/settings.h b/common/settings.h
index 48b9ed700346e5f43a0759bb69326304b8326404..f8bc41750acaa5dc4a8307c51bc779ac3fe347e1 100644
--- a/common/settings.h
+++ b/common/settings.h
@@ -17,6 +17,8 @@ struct Settings {
   // Port on target will be auto selected by the OS. A message will be printed
   // on the target with the port after it has been selected.
   uint32_t observatory_port = 0;
+  bool enable_diagnostic = false;
+  uint32_t diagnostic_port = 0;
   bool start_paused = false;
   bool trace_startup = false;
   bool endless_trace_buffer = false;
diff --git a/shell/common/diagnostic/diagnostic_server.cc b/shell/common/diagnostic/diagnostic_server.cc
index 2fc0c3cfc415acff104525829600beea4fe5a0a7..a7a3f02224ff4a10547a6d46d411eb745dd31d1f 100644
--- a/shell/common/diagnostic/diagnostic_server.cc
+++ b/shell/common/diagnostic/diagnostic_server.cc
@@ -31,6 +31,7 @@ using tonic::DartLibraryNatives;
 using blink::EmbedderResources;
 using tonic::DartInvokeField;
 using tonic::LogIfError;
+using tonic::ToDart;
 
 namespace {
 
@@ -60,7 +61,7 @@ void SendNull(Dart_Port port_id) {
 
 DART_NATIVE_CALLBACK_STATIC(DiagnosticServer, HandleSkiaPictureRequest);
 
-void DiagnosticServer::Start() {
+void DiagnosticServer::Start(uint32_t port) {
   if (!g_natives) {
     g_natives = new DartLibraryNatives();
     g_natives->Register({
@@ -91,7 +92,7 @@ void DiagnosticServer::Start() {
 
   FTL_CHECK(!LogIfError(Dart_FinalizeLoading(false)));
 
-  DartInvokeField(Dart_RootLibrary(), "diagnosticServerStart", {});
+  DartInvokeField(Dart_RootLibrary(), "diagnosticServerStart", {ToDart(port)});
 }
 
 void DiagnosticServer::HandleSkiaPictureRequest(Dart_Handle send_port) {
diff --git a/shell/common/diagnostic/diagnostic_server.dart b/shell/common/diagnostic/diagnostic_server.dart
index cc7aeaec7266dac2b8f8c5a2593fe76873ea6c5e..6779713f7ff9e6e4e1f5449a794f076e255b9a90 100644
--- a/shell/common/diagnostic/diagnostic_server.dart
+++ b/shell/common/diagnostic/diagnostic_server.dart
@@ -11,8 +11,8 @@ import 'dart:typed_data';
 void handleSkiaPictureRequest(SendPort sendPort)
     native 'DiagnosticServer_HandleSkiaPictureRequest';
 
-void diagnosticServerStart() {
-  HttpServer.bind('127.0.0.1', 0).then((HttpServer server) {
+void diagnosticServerStart(int port) {
+  HttpServer.bind('127.0.0.1', port).then((HttpServer server) {
     server.listen(dispatchRequest, cancelOnError: true);
 
     String ip = server.address.address.toString();
diff --git a/shell/common/diagnostic/diagnostic_server.h b/shell/common/diagnostic/diagnostic_server.h
index 00553ca2e35962b206a488fbc425e8a08e2f4fda..b5f9e1d00bb5f7c233e353aaa0993f873e832b7e 100644
--- a/shell/common/diagnostic/diagnostic_server.h
+++ b/shell/common/diagnostic/diagnostic_server.h
@@ -11,7 +11,7 @@ namespace shell {
 
 class DiagnosticServer {
  public:
-  static void Start();
+  static void Start(uint32_t port);
   static void HandleSkiaPictureRequest(Dart_Handle send_port);
 
  private:
diff --git a/shell/common/shell.cc b/shell/common/shell.cc
index b60999b9559f2f273d1a5edb5b30d584343d0fc4..9c64802c0eedf312255b3d936cd6ad3971306afe 100644
--- a/shell/common/shell.cc
+++ b/shell/common/shell.cc
@@ -42,6 +42,18 @@ bool IsViewInvalid(const ftl::WeakPtr<PlatformView>& platform_view) {
   return !platform_view;
 }
 
+template <typename T> bool GetSwitchValue(const base::CommandLine& command_line,
+                                          Switch sw, T* result) {
+  auto port_string = command_line.GetSwitchValueASCII(FlagForSwitch(sw));
+  std::stringstream stream(port_string);
+  T value = 0;
+  if (stream >> value) {
+    *result = value;
+    return true;
+  }
+  return false;
+}
+
 class NonDiscardableMemory : public base::DiscardableMemory {
  public:
   explicit NonDiscardableMemory(size_t size) : data_(new uint8_t[size]) {}
@@ -66,8 +78,8 @@ base::LazyInstance<NonDiscardableMemoryAllocator> g_discardable;
 void ServiceIsolateHook(bool running_precompiled) {
   if (!running_precompiled) {
     const blink::Settings& settings = blink::Settings::Get();
-    if (settings.enable_observatory)
-      DiagnosticServer::Start();
+    if (settings.enable_diagnostic)
+      DiagnosticServer::Start(settings.diagnostic_port);
   }
 }
 
@@ -135,19 +147,26 @@ void Shell::InitStandalone(std::string icu_data_path,
 
   // Set Observatory Port
   if (command_line.HasSwitch(FlagForSwitch(Switch::DeviceObservatoryPort))) {
-    auto port_string = command_line.GetSwitchValueASCII(
-        FlagForSwitch(Switch::DeviceObservatoryPort));
-    std::stringstream stream(port_string);
-    uint32_t port = 0;
-    if (stream >> port) {
-      settings.observatory_port = port;
-    } else {
+    if (!GetSwitchValue(command_line, Switch::DeviceObservatoryPort,
+                        &settings.observatory_port)) {
       FTL_LOG(INFO)
           << "Observatory port specified was malformed. Will default to "
           << settings.observatory_port;
     }
   }
 
+  settings.enable_diagnostic =
+      !command_line.HasSwitch(FlagForSwitch(Switch::DisableDiagnostic));
+
+  if (command_line.HasSwitch(FlagForSwitch(Switch::DeviceDiagnosticPort))) {
+    if (!GetSwitchValue(command_line, Switch::DeviceDiagnosticPort,
+                        &settings.diagnostic_port)) {
+      FTL_LOG(INFO)
+          << "Diagnostic port specified was malformed. Will default to "
+          << settings.diagnostic_port;
+    }
+  }
+
   settings.start_paused =
       command_line.HasSwitch(FlagForSwitch(Switch::StartPaused));
 
diff --git a/shell/common/switches.h b/shell/common/switches.h
index 33692a5b1a21c22eb70b483ec27e8f912be92ef7..631b4ed8c099ac158c29ce8b2e4d18f6f9010b0a 100644
--- a/shell/common/switches.h
+++ b/shell/common/switches.h
@@ -43,6 +43,13 @@ DEF_SWITCH(DisableObservatory,
            "disable-observatory",
            "Disable the Dart Observatory. The observatory is never available "
            "in release mode.")
+DEF_SWITCH(DeviceDiagnosticPort,
+           "diagnostic-port",
+           "A custom diagnostic server port.")
+DEF_SWITCH(DisableDiagnostic,
+           "disable-diagnostic",
+           "Disable the diagnostic server. The diagnostic server is never "
+           "available in release mode.")
 DEF_SWITCH(EnableDartProfiling,
            "enable-dart-profiling",
            "Enable Dart profiling. Profiling information can be viewed from "