Flutter MCP CLI Runtime Validation

Use this skill when you need agent-style runtime validation through flutter-mcp-toolkit with minimal operator steps.

Two-Step Flow

1. Launch the Flutter app in debug mode.
2. Run one CLI command:

dart run mcp_server_dart/bin/flutter_mcp_toolkit.dart --save-images --output-dir .flutter_mcp/runtime_validation validate-runtime \
  --target ws://127.0.0.1:8181/<token>/ws \
  --timeout-ms 10000 \
  --post-reload-delay-ms 500 \
  --after-reload

Optional skill install in the same command:

dart run mcp_server_dart/bin/flutter_mcp_toolkit.dart validate-runtime \
  --target ws://127.0.0.1:8181/<token>/ws \
  --install-skill

Permission behavior for this flow:

• validate-runtime stays read/write only for visual capture and defaults to auto_request_once.
• doctor remains read-only.
• On macOS, Screen Recording permission belongs to the host process running flutter-mcp-toolkit.
• On web, flutter_layer is the only supported truth path and no OS permission prompt is expected.
• If the first capture_ui_snapshot attempt uses host desktop_window and fails (common on macOS when the window is not foregrounded, or for iOS Simulator), validate-runtime automatically retries once with flutter_layer.
• You may pass the VM URI as global --vm-service-uri instead of validate-runtime --target when only one URI is needed.

What validate-runtime Must Prove

• Doctor preflight passes critical checks.
• Required toolkit extensions exist:
  • ext.mcp.toolkit.app_errors
  • ext.mcp.toolkit.view_details
  • ext.mcp.toolkit.view_screenshots
  • ext.mcp.toolkit.inspect_widget_at_point
• Screenshot capture works.
• View details (layout metadata) are available.
• App errors are retrievable.
• If --after-reload is enabled, post-reload screenshot also works.

Output Handling

• Use data.summary as pass/fail status for automation.
• Use data.summary.captureFallbackUsed to see whether the flutter_layer retry succeeded after a failed desktop_window attempt.
• Use data.steps for per-step evidence and retries.
• Use data.doctor.checks to explain setup blockers.
• Use data.summary.screenshotFiles for saved screenshot paths when --save-images is enabled.
• When --save-images is enabled, read screenshot file URLs from step data.
• For visual debugging reports, also run:
  • exec --name capture_ui_snapshot --args '{"errorsCount":4,"compress":true,"includeViewDetails":true,"includeErrors":true}'
  • exec --name inspect_widget_at_point --args '{"x":<int>,"y":<int>}'

Failure Rules

• If toolkit extensions are missing, stop and report instrumentation gap with exact fix:
  • add mcp_toolkit to app dependencies
  • ensure MCPToolkitBinding.instance.bootstrapFlutter(...) or equivalent manual initialization runs before runApp
  • hot restart or rerun the app
• If first explicit URI connect fails, retry is automatic for retryable connection errors.
• If screenshots are blank, verify app window is visible and retry.
• If macOS visual capture is denied, use:
  • dart run mcp_server_dart/bin/flutter_mcp_toolkit.dart permissions status
  • dart run mcp_server_dart/bin/flutter_mcp_toolkit.dart permissions request
  • dart run mcp_server_dart/bin/flutter_mcp_toolkit.dart permissions open-settings
• If app cannot be instrumented, do not claim screenshot/layout/error inspection success.

Visual QA + Source Mapping Rules

• Always compare before/after screenshot evidence around changes.
• For each reported visual issue, provide coordinate + inspect_widget_at_point output.
• Map defects to source using get_app_errors top stack frame (file, line, column) when available.
• Do not use debug_dump_* unless explicitly requested.

Challenge Cases (Always Call Out Explicitly)

• No running debug app: doctor critical failure on vm_target_reachable; request app launch before continuing.
• Wrong target URI/token: treat as connection mismatch and retry with exact app.debugPort.wsUri.
• Toolkit added but still missing extensions: hot reload is often insufficient, require hot restart/full rerun.
• Non-modifiable app (cannot add toolkit): report inspection as unavailable instead of guessing.

Source: Arenukvern/mcp_flutter — distributed by TomeVault.