marionette-flutter

name

marionette-flutter

description

Expert guidance for Marionette MCP, enabling AI agents to inspect and interact with running Flutter applications. Use when (1) setting up Marionette in a Flutter project, (2) configuring MCP server for Codex or Cursor, (3) automating UI testing with tap, enter_text, scroll_to, or take_screenshots, (4) debugging Flutter apps by inspecting widget trees or retrieving logs, (5) performing smoke tests or verifying user flows, (6) using replay mode to re-run recorded test sessions. Triggers include marionette, MCP server, flutter testing, widget inspection, UI automation, VM service, replay.

Marionette Flutter

Marionette MCP enables AI agents to inspect and interact with running Flutter applications at runtime. It's "Playwright MCP, but for Flutter apps."

Quick Setup

1. Add Package to Flutter App

# pubspec.yaml
dev_dependencies:
  marionette_flutter: ^0.4.0

2. Initialize Binding (Debug Mode Only)

// main.dart
import 'package:flutter/foundation.dart';
import 'package:marionette_flutter/marionette_flutter.dart';

void main() {
  if (kDebugMode) {
    MarionetteBinding.ensureInitialized();
  }
  runApp(const MyApp());
}

Logging options (choose one):

// Option 1: Dart logging package
import 'package:marionette_logging/marionette_logging.dart';
MarionetteBinding.ensureInitialized(
  MarionetteConfiguration(logCollector: LoggingLogCollector()),
);

// Option 2: logger package
import 'package:marionette_logger/marionette_logger.dart';
MarionetteBinding.ensureInitialized(
  MarionetteConfiguration(logCollector: LoggerLogCollector()),
);

// Option 3: Default (PrintLogCollector) — no extra import needed

3. Install MCP Server

dart pub global activate marionette_mcp

4. Configure AI Tool

Codex (.Codex/mcp.json):

{
  "mcpServers": {
    "marionette": {
      "command": "dart",
      "args": ["run", "marionette_mcp"]
    }
  }
}

Cursor (.cursor/mcp.json):

{
  "mcpServers": {
    "marionette": {
      "command": "marionette_mcp"
    }
  }
}

5. Connect to Running App

Run Flutter app in debug mode, find VM Service URI in console:

The Dart VM service is listening on http://127.0.0.1:12345/AbCdEfGh=/

Connect using ws://127.0.0.1:12345/AbCdEfGh=/ws

Version check: On connect, marionette_mcp verifies its version matches marionette_flutter. Mismatches fail with a clear error — update both packages together.

Available Tools

Tool	Purpose
connect	Connect to Flutter app via VM Service URI
disconnect	Disconnect from current app
get_interactive_elements	List visible UI elements (buttons, inputs, etc.)
tap	Tap element by key or visible text
enter_text	Enter text by key or into focused element
scroll_to	Scroll until element is visible (auto-reverses direction)
take_screenshots	Capture base64-encoded screenshots
get_logs	Retrieve logs from configured log collector
hot_reload	Apply code changes without state loss
list_custom_extensions	Discover app-registered VM service extensions
call_custom_extension	Call an app-specific VM service extension

Text Entry

enter_text accepts exactly one of:

• key: Target by ValueKey — enter_text(key: "email_field", input: "hello")
• focused_element: true: Target currently focused field — tap a field first, then enter_text(focused_element: true, input: "hello")

onChanged callbacks are triggered properly.

Custom Extensions

Apps can register VM service extensions. Discover them with list_custom_extensions, then call with call_custom_extension(extension: "extensionName", args: {}).

Custom Widget Configuration

Register custom interactive widgets so marionette can discover them:

MarionetteBinding.ensureInitialized(
  configuration: MarionetteConfiguration(
    customInteractiveWidgets: [
      CustomWidget<MyButton>(
        type: InteractiveElementType.button,
        getText: (widget) => widget.label,
      ),
    ],
  ),
);

Session Mode (Replay Support)

At the start of every test session, ask the user:

"Is this a replay of a previous session, or a new session?"

• New session: Execute tests normally and record actions to the replay folder.
• Replay: Load and follow the replay file. Report as bug if a step cannot be followed (flexible on data changes like updated prices/text).

See references/replay-mode.md for full replay format and rules.

Common Workflows

Smoke Test After Refactor

1. Connect to running app
2. get_interactive_elements to see current screen
3. tap buttons to navigate
4. take_screenshots to verify visual state
5. get_logs to check for errors

Form Testing

1. get_interactive_elements to find text fields
2. enter_text to fill form (by key or focused element)
3. tap submit button
4. get_logs to verify submission

UI Debugging

1. Connect to app
2. get_interactive_elements to inspect widget tree
3. Identify missing or misplaced elements
4. hot_reload after fixes

Limitations

• Debug/profile mode only — requires VM Service (not available in release)
• Manual URI connection — must copy URI from console each run
• Custom widgets need configuration — register non-standard interactive widgets