Violentmonkey is a mature, open-source browser extension for managing and executing userscripts across Chrome, Firefox, Edge, and other WebExtensions-compatible browsers. The extension provides a full lifecycle for userscripts: installation from URLs or files, automatic updates, syntax-highlighted editing (via CodeMirror 5), per-script configuration, and a dashboard for bulk operations. Its architecture comprises a background service worker (MV3) or background page (MV2), content scripts injected into web pages (with separate realms for page-level GM API execution and content-level bridge), a popup interface, an options dashboard, an installation confirmation page, and an offscreen document for cross-origin requests under MV3. The system integrates multiple sync backends (Dropbox, Google Drive, OneDrive, WebDAV, S3-compatible), supports i18n with 30+ locales via Transifex, and includes custom build tooling for multi-browser packaging. While the core domain is userscript management, the codebase demonstrates sophisticated patterns for secure script injection, anti-spoofing (safe globals), reactive settings, and concurrency-limited storage operations.
ScriptCat is a sophisticated browser extension for managing userscripts with advanced AI agent capabilities. It features a multi-context architecture (content scripts, service worker, offscreen documents, popup/options UI) built with React, TypeScript, and modern web extension APIs. The extension provides userscript installation, execution, synchronization, network rule management, and an integrated AI chat interface with tool execution capabilities. Its architecture demonstrates strong separation of concerns and implements several reusable patterns for cross-context communication, storage abstraction, and caching.
Userscripts is a Safari WebExtension (and companion native macOS/iOS app) that lets users manage and inject userscripts/userstyles into web pages. It provides a popup for toggling scripts and checking updates, a full-featured code editor (CodeMirror 5) for editing scripts, and native apps that store scripts in a local filesystem directory. The extension communicates with the native app via Safari's native messaging, and supports all major Greasemonkey API methods, match patterns, and metadata blocks. The project uses Svelte+Vite for all UI surfaces, Swift for native platforms, and Xcode project with Fastlane for deployment. It is a polished, well-architected tool that fills a gap left by Safari's limited extension ecosystem.