extension.js

The premium Open Source alternative to Plasmo

🎯 Best for:Developers building modern, cross-browser extensions with minimal configuration.

What is extension.js?

Replaces manual WebExtension boilerplate and complex Webpack/Vite configurations. Provides a zero-config development environment with native hot-reloading for Chrome, Firefox, and Safari.

Tech Stack
TypeScriptFrontend & Headless CMS

Why extension.js?

  • Automatic manifest generation
  • Built-in TypeScript support
  • Fast hot-module replacement

Limitations

  • Newer ecosystem
  • Opinionated file structure
  • Limited plugin ecosystem
3/6/2026
Last Update
127
Forks
10
Issues
MIT
License
Financial Leak Detected

Stop the "SaaS Tax"

Your team could be burning cash. Switching to extension.js instantly boosts your runway.

Competitor Cost
-$1,440
/ year (est. based on Plasmo)
Self-Hosted
$0
/ year
Team Size10 Users
150+
SAVE 100%

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