InjectJS is a free, open-source Chrome extension that lets you inject custom JavaScript into any website you visit. Whether you want to automate repetitive tasks, customize the appearance of a site, block annoying elements, or test code against a live page, InjectJS gives you the tools to do it — right from your browser.
The web is full of small annoyances: pop-ups that won't go away, workflows that require too many clicks, and pages that don't look quite right. Browser developer tools let you run JavaScript on a page, but your changes disappear the moment you reload. InjectJS solves that problem. Scripts you create persist across page loads and run automatically on the sites you choose.
InjectJS was built out of a personal need to run persistent scripts without the overhead of building a full browser extension for every small task. It started as a simple tool and has grown into a platform with a community script repository, a full web dashboard, and support for advanced features like match patterns and trigger timing.
InjectJS supports three trigger modes — run scripts before the page loads, after the page loads, or manually from the right-click context menu. Scripts are targeted to specific websites using Chrome match patterns, so you have precise control over where your code runs.
The web dashboard at injectjs.net provides a full script management experience with a code editor that includes syntax highlighting and ESLint linting. You can also import and export your entire script collection as a zip bundle, making it easy to back up your setup or move it between machines.
The community script repository lets users browse, install, and share scripts. Every submitted script goes through an approval process before appearing in the repository. You can upvote scripts you find useful and install them with a single click.
InjectJS is used by web developers who want to test changes on live sites, QA engineers who need to inject test scripts or mock data, product managers who want to prototype UI tweaks, and everyday users who want to customize the websites they visit. If you've ever wished a website worked a little differently, InjectJS is for you.
InjectJS does not collect or transmit any personal data from the extension. All scripts and preferences are stored locally in your browser. The web dashboard uses standard analytics (Google Analytics and Vercel Analytics) to understand traffic patterns, but no script content or browsing data is ever sent to our servers. You can read the full privacy policy for details.
Have a question, feature request, or bug report? You can reach out via email at dcohen613@gmail.com or submit feedback through the feedback portal.