Supercharging UI Development with Flutter's Widget Previewer

Flutter has always been praised for its fast development cycle and hot reload. Now, with the introduction of the Widget Previewer (experimental as of Flutter 3.35), building and testing UI components just got even faster.

What is the Widget Previewer?

The Widget Previewer is a tool that lets you render Flutter widgets directly in Chrome without needing to spin up your entire app. Think of it as a design playground: you can preview widgets in isolation, tweak them quickly, and see instant updates.

Getting Started

To use the Widget Previewer, you’ll need Flutter 3.35+ and Chrome installed.

1. Open your Flutter project.

2. Run:

    flutter widget-preview start
   

   This will open a preview workspace in your browser with hot reload enabled.

Adding Previews with @Preview

Widgets are previewed by annotating them with the @Preview annotation from package:flutter/widget_previews.dart.

Supported targets:

• Static methods that return a widget

• Top-level widget-returning functions

• Public widget constructors/factories (with no required args)

Example

import 'package:flutter/material.dart';
import 'package:flutter/widget_previews.dart';

@Preview(name: 'My Sample Text')
Widget mySampleText() {
  return const Text('Hello, World!');
}

@Preview(name: 'My Sample ListView')
Widget mySampleListView() {
  return Scaffold(
    appBar: AppBar(
      title: const Text('ListView'),
    ),
    body: ListView.separated(
      itemCount: 5,
      itemBuilder: (_, i) {
        return ListTile(
          tileColor: Colors.white,
          shape: RoundedRectangleBorder(
            side: const BorderSide(
              color: Color(0xFFE0E0E0),
            ),
            borderRadius: BorderRadius.circular(12),
          ),
          onTap: () {},
          title: Text(
            'Serial Number: $i',
            style: const TextStyle(
              fontWeight: FontWeight.w500,
            ),
          ),
          subtitle: Text('Description $i'),
          trailing: const Icon(Icons.info_outlined),
        );
      },
      separatorBuilder: (BuildContext context, int index) {
        return const SizedBox(height: 12);
      },
    ),
  );
}

This example demonstrates how you can quickly preview a ListView inside a Scaffold and you can preview multiple widgets simultaneously. The annotation @Preview makes it show up in the preview workspace instantly.

Preview Controls

Each preview comes with handy UI tools:

• Zoom (in, out, reset)

• Theme toggle (light/dark)

• Hot restart for individual previews or the whole workspace

Limitations

Since the previewer runs as a Flutter Web app, there are some caveats:

• No dart:io or native plugins.

• Only web-compatible plugins may work.

• Must use package-based asset paths (e.g., 'packages/my_pkg/assets/img.png').

• Unconstrained widgets will get auto constraints (best to specify size).

• Annotation arguments must be public constants (for now).

Why Use It?

• Speed: Test UI variations instantly without navigating through your app.

• Focus: Build widgets in isolation, free from app-level state.

• Design workflow: Great for iterating on styles, themes, and layouts.

Final Thoughts

The Widget Previewer is still experimental, but it’s a game-changer for UI-heavy projects. By reducing iteration friction, it brings Flutter closer to the design-first workflows that front-end developers and designers love.

If you’re already on Flutter 3.35 or higher, give it a spin—you’ll wonder how you lived without it!

Check the flutter documentation for Widget Previewer here.