This is the Microsoft FAST monorepo, a standards-based web component framework. It provides a lightweight, performant foundation for building custom elements with declarative templates, reactive data binding, server-side rendering (SSR), and hydration. The core library `@microsoft/fast-element` offers a complete runtime with observability, templating, dependency injection, and state management. Companion packages include a client-side router (`fast-router`), a test harness (`fast-test-harness`), and Rust-based build tools (`fast-build`, `fast-convert`) for SSR and template syntax conversion. The repository also contains example applications (CSR todo, SSR chat, WebUI todo), extensive Playwright integration tests, and a benchmark suite measuring rendering performance. The architecture is modular, with clear separation between runtime, build-time, and testing concerns. The codebase demonstrates high craftsmanship in areas like reactive observation, template compilation, hydration, and dependency injection, though some experimental features and cross-language (Rust/TypeScript) coordination introduce maintenance complexity.