multi_device_preview_marionette

Lets AI agents drive multi_device_preview through Marionette MCP: every preview command becomes an MCP tool with a typed schema.

Tool	What it does
`multiDevicePreview.getState`	Devices (preset, text scale, size, screen key, out-of-sync) and sync state
`multiDevicePreview.listPresets`	Preset ids
`multiDevicePreview.setSync`	Turns input sync on or off
`multiDevicePreview.restart`	Rebuilds every app from scratch
`multiDevicePreview.setDevice` / `addDevice` / `removeDevice`	Changes the devices
`multiDevicePreview.saveScreenshot`	Writes a PNG of all devices, or one, to a file
`multiDevicePreview.panZoom`	Scrolls with a trackpad gesture, mirrored like a real one

Setup

flutter pub add dev:multi_device_preview_marionette dev:marionette_flutter

In the preview entry point, initialize Marionette before runMultiDevicePreview:

import 'package:flutter/foundation.dart';
import 'package:marionette_flutter/marionette_flutter.dart';
import 'package:multi_device_preview/multi_device_preview.dart';
import 'package:multi_device_preview_marionette/multi_device_preview_marionette.dart';

void main() {
  final controller = MultiDevicePreviewController();
  if (!kReleaseMode) {
    MarionetteBinding.ensureInitialized(
      multiDevicePreviewMarionetteConfiguration,
    );
    registerMultiDevicePreviewMarionetteExtensions(controller);
  }
  runMultiDevicePreview(
    controller: controller,
    appBuilder: (context, slot) => const MyApp(),
  );
}

multiDevicePreviewMarionetteConfiguration uses CompactionMode.none, so get_interactive_elements reports every element and an agent can compare sizes and text scales across devices. Pass your own MarionetteConfiguration to customize it.

Tips for agents

Each device screen has the key multi_device_preview.screen.<n>. Pass it in ancestor_keys to look at, or act on, a single device. Without it, keys and texts match the first device, and the action is mirrored to the others while input sync is on.
Prefer multiDevicePreview.saveScreenshot over take_screenshots: several devices easily exceed the size of an MCP response.
macOS stops rendering a window hidden behind other windows; keep the preview window visible, or saveScreenshot reports an error.
bounds from Marionette: x/y are positions in the scaled window, width/height are logical sizes inside the device.

License

MIT

multi_device_preview_marionette

Setup

Tips for agents

License

Libraries

multi_device_preview_marionette package