# FAQ

## Is Widgetbook free?

Yes.
Widgetbook is [open source](https://github.com/widgetbook/widgetbook) and free.
[Widgetbook Cloud](/cloud) is a separate, optional product for hosted builds and visual reviews.

## Do I need a separate package for Widgetbook?

Yes.
Widgetbook lives in its own package that depends on your app or design system.
[`widgetbook init`](/cli/commands/init) sets it up.
To catalog several packages from one Widgetbook, see [Widgetbook in a Monorepo](/configure/monorepo).

## What is the difference between an Arg and a Mode?

[Args](/args/overview) control the widget's properties: text, color, state.
They come from the widget's constructor.

[Modes](/addons/modes) control the environment: theme, locale, viewport, text scale.
They come from [Addons](/addons/overview).

See [Core Concepts](/core-concepts).

## `_Story` and `_Args` are undefined

Both are generated.
Check the stories file has a `part` directive and a `Meta` declaration, then run the generator.

```dart title="widgetbook/lib/button.stories.dart"
part 'button.stories.g.dart';

const meta = Meta(Button.new);
```

```bash
dart run build_runner build
```

Use `dart run build_runner watch` during development.
See [Code Generation](/stories/code-generation).

## Why does a bare `_Story()` not compile?

Constructor parameters without a usable default must be passed through `args`.
A required `onPressed` has no default, so the story needs `onPressed: Arg.fixed(() {})`.

Widgets whose parameters are all optional or defaulted work with `_Story()`.
See [Quick Start](/quick-start).

## How do I catalog a screen that fetches data?

Mock the dependency and inject it with the story's `setup` hook: a `ProviderScope`, a `BlocProvider`, a stubbed repository.
See [Mocking](/stories/mocking).

## Do I have to write visual tests?

No.
Write [Scenarios](/testing/overview).
`flutter test` captures a screenshot of each one.
With [Widgetbook Cloud](/cloud) those snapshots are diffed on every pull request.
See [What are Visual Tests?](/testing/visual-tests).

## Where do snapshots go?

`build/.widgetbook` in your Widgetbook package.
See [Run Scenarios](/testing/run-scenarios).

## Does Widgetbook work with Cupertino or a custom design system?

Yes.

| App type | Addon |
| --- | --- |
| `MaterialApp` | `MaterialThemeAddon` |
| `CupertinoApp` | `CupertinoThemeAddon` |
| Custom theme | `ThemeAddon` |

See [Theme Addon](/addons/theme-addon).

## Does Widgetbook collect data?

It reports anonymous usage data after `build_runner build`, and no personal data.
[Telemetry](/telemetry) lists what is sent and how to opt out.

## How do I upgrade from v3?

See the [v4 Migration Guide](/v4-migration).
It recommends writing a few v4 stories by hand first, then using an agent primed with your conventions.
A manual workflow is at the end of the page.

## Where do I get help?

[Discord](https://discord.gg/zT4AMStAJA), or [Resources](/resources) for talks, articles, and example projects.