Why Flutter Web Release Loads Slowly
- Big JS Bundle
- Flutter compiles your Dart code into JavaScript (
main.dart.js). - This file can be 5–10 MB (or more if you use many packages).
- First-time users must download this entire file.
- Flutter compiles your Dart code into JavaScript (
- CanvasKit Rendering
- By default, Flutter Web uses CanvasKit (a WebAssembly engine for drawing).
- The CanvasKit WASM + fonts + JS adds a few MB extra.
- First load = slow, but cached later.
- Fonts & Assets
- Custom fonts and images increase load time.
- Flutter embeds fonts into the app.
- No Code-Splitting
- Unlike React/Angular, Flutter bundles everything into one big JS file.
- Even if you only need a small page, the whole app must load.
- Hosting/Server Speed
- If you’re hosting on slow servers (or no CDN), the download is slower.
- On free hosting (like GitHub Pages), initial load may be 5–10 sec.
How to Improve Load Speed
- Use
--releasebuild (already does optimizations)flutter build web --release - Enable Tree Shaking for Icons
If you usematerialicons:flutter build web --release --pwa-strategy=offline-firstOr add topubspec.yaml:flutter: uses-material-design: trueThis removes unused icons. - Use WebRenderer = html (lighter but less accurate graphics)
flutter build web --release --web-renderer htmlhtml: smaller, faster load, but less accurate animations.canvaskit: better quality, heavier.
- Compress Assets & Fonts
- Use only required fonts.
- Convert PNG → WebP.
- Remove unused assets.
- Enable GZIP/Brotli Compression on Server
- If hosting on Nginx/Apache/Cloudflare, enable compression.
- Reduces JS size by 70%+.
- Host on a CDN (Firebase Hosting, Vercel, Netlify)
- Faster delivery worldwide.
- Built-in caching.
- Use Service Worker (PWA)
- Offline-first caching makes subsequent loads instant.
First-time load will always be slower (user must download ~2–6 MB).
But with compression + html renderer + caching, you can make it 2–3 sec even on average internet.
