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Inject custom JavaScript code into any website

Code Injector is a powerful userscript manager that lets you run custom JavaScript snippets and inject code on any website automatically or on demand.

KEY FEATURES

• Flexible URL patterns — match by exact domain, wildcard (*.example.com), path, port, or full URL. Use * to target all sites. • Auto and manual modes — scripts run automatically on page load, or only when you click the ▶ button. • Built-in code editor — full-featured editor with JavaScript syntax highlighting and real-time error detection. • Fullscreen editing — expand the code editor to a fullscreen overlay for comfortable work on complex scripts. • Drag & drop ordering — reorder your rules with smooth animated drag and drop. • Light and dark themes — follows your browser theme automatically, or set it manually. • 12 languages — English, Russian, Chinese, Japanese, Korean, Spanish, French, German, Arabic, Georgian, Turkish, and Kazakh. • Enable / disable rules — toggle individual rules on and off without deleting them. • Domain-aware filtering — filter your rules list to show only those matching the current site. • All data stored locally — your rules are saved in chrome.storage.local; nothing is sent to external servers.

TYPICAL USE CASES

— Add custom styles or scripts to sites that don't offer personalization. — Automate repetitive browser tasks (fill forms, click buttons, collect data). — Debug and prototype front-end changes directly on production sites. — Inject analytics, logging, or monitoring snippets for development. — Debug and prototype front-end changes, test UI variations, or fix layouts directly on production sites.

HOW IT WORKS

1. Click the extension icon in the toolbar.
2. Click "Add" to create a new rule.
3. Enter a URL pattern (e.g. *.example.com).
4. Write your JavaScript code.
5. Save. The script will execute on every matching page load.

For manual rules, check the "Manual" checkbox — the script won't run automatically, but you can trigger it anytime with the ▶ button.

Built with Manifest V3, chrome.scripting API, and Vanilla JS. No external dependencies at runtime.