User JavaScript and CSS

User JavaScript and CSS on any website

Write your own JavaScript and CSS for any website: hide what gets in the way, add a missing button, fix a layout. A rule pairs your code with the sites it runs on, and the extension applies it every time you open them. What's new in each version: https://tenrabbits.github.io/user-js-css-docs/changelog Editor - Side-by-side JavaScript and CSS editors with syntax highlighting, Prettier formatting and 13 themes - SCSS and Sass out of the box; the preprocessor can be turned off for a rule - Styles update on open tabs as you save — no reload needed - The last 10 versions of each rule are kept, so a bad edit is one click away from undo Rules and sites - Several URL patterns per rule, with exclusions: !https://example.com/admin/* - Styles can apply inside nested frames and open shadow DOM — per rule - Any rule can serve as a template for new ones or as a module for other rules Libraries - Add jQuery or any script and style by URL; files are stored locally and update daily, weekly or on demand Backup - Export and import in JSON — pick which rules to import - Backup to the browser's sync storage In Chrome - JavaScript needs your permission: turn on "Allow user scripts" on the extension's details page (Chrome 138 and later) or Developer mode (earlier versions). The settings page shows where. Styles work without it AI agent tools (experimental). Let an agent on your computer — Claude Code, Cursor, Codex, VS Code and other MCP clients — manage your rules. Off by default; enable in Settings → MCP. The connection is local only: the extension connects to ws://127.0.0.1:8767, served by the user-js-css-mcp server your agent starts. Nothing leaves your machine; both sides verify a shared secret. The agent can read and change your rules; the secret is never included in exports. Turn it off with the same switch. Server: https://www.npmjs.com/package/user-js-css-mcp Privacy. No ads, no analytics, no data collection. Your code stays in your browser; the extension only downloads the libraries you add. The interface is in English, Russian, Korean, Japanese, Simplified Chinese, Brazilian Portuguese, French, German and Spanish. A personal, non-commercial project. Documentation: https://tenrabbits.github.io/user-js-css-docs/