Custom JS Runner

Write JavaScript for any website and have it run automatically every time you visit.

Custom JS Runner lets you run your own JavaScript on any website. Open the popup on a site, write some code and press Save & Run. Your script runs right away, and again every time you come back to that site. FEATURES • A real code editor in the popup, with syntax highlighting, line numbers and auto-indent • Turn a site's script on or off with one switch • Several scripts per site, each in its own tab • Choose when a script runs: before the page's own scripts, when the DOM is ready, or after the page loads • Run in an isolated world (safe from the page's code) or in the page's own world, so you can use the site's variables and functions • Match sites by domain, or with full match patterns like https://*.example.com/* or <all_urls> • A full-page editor for managing all your scripts, with search • Import and export your scripts as JSON • Light and dark mode GOOD FOR • Hiding annoying elements or banners • Tweaking layouts and styles • Auto-filling or automating repetitive steps • Adding small features to sites you use every day • Debugging and prototyping PRIVATE BY DESIGN Your scripts are stored only on your computer. There are no servers, no accounts, no analytics and no tracking. SETUP NOTE Chrome asks you to approve user scripts once. After installing, open the extension's Details page in chrome://extensions and turn on "Allow User Scripts". The extension shows a button that takes you there.