JS Mage is a robust Chrome extension designed for advanced users who want to inject custom JavaScript directly into web pages. This utility bypasses standard extension isolation and Content Security Policy (CSP) restrictions, allowing users to interact with the host page's window object and native variables seamlessly. With its draggable, resizable code editor integrated via Shadow DOM, the user interface remains unaffected by the host page's CSS, ensuring a smooth editing experience.

Key features include the ability to maintain independent scripts for specific hostnames or apply a global script across all sites. Users can execute scripts manually or automatically upon page load. The in-page editor supports various syntax highlighting themes, a built-in code formatter, and a comprehensive undo/redo history. Additional functionalities such as state backup, export options, and a master power toggle enhance usability, making JS Mage a powerful tool for developers looking to customize their browsing experience.