ScriptCat is a browser extension (Chrome MV3 and Firefox) that serves as a full-featured user script manager, compatible with Tampermonkey/Greasemonkey metadata. It allows users to install, edit, enable/disable, and organize user scripts that run on web pages. Beyond script management, it integrates an AI Agent subsystem providing chat, tool calling, MCP server support, task scheduling, and skill execution. The extension also includes cloud sync and backup via multiple cloud storage providers (WebDAV, OneDrive, Google Drive, Dropbox, Baidu, S3), a built-in Monaco code editor with ESLint integration, network rule management using Chrome's DeclarativeNetRequest API, and an external access system for remote control (e.g., VS Code integration via WebSocket). Architecturally, the extension uses a service worker as the main background process, content scripts injected into web pages, an offscreen document for sandboxed execution, and a popup/options page for UI. Communication between these contexts is handled by a custom message passing framework (packages/message) that supports multiple transport modes (custom event, window message, chrome.runtime). Data is stored in chrome.storage (local/sync/session) and OPFS (file-based storage for agent data). The UI is built with React and Radix UI, with a comprehensive set of reusable UI components. Notable features include a sophisticated AI agent system with context window budgeting, tool call loop detection, sub-agent orchestration, and provider-agnostic LLM integration. The filesystem abstraction layer provides a clean provider pattern for cloud storage backends. The project also includes extensive testing (Vitest unit tests, Playwright E2E tests) and internationalization support for 10 languages. The codebase demonstrates strong engineering practices with clean abstractions, well-separated packages, and reusable components. While primarily an application, it contains data-processing elements in the agent system and cloud sync features, but these are integrated as application features rather than standalone data pipelines.