A Progressive Web App requires just three things beyond your existing website: a Web App Manifest JSON file that defines the app’s name, icons, and display mode; a service worker that intercepts network requests for offline support and caching; and HTTPS hosting. Add these to any site with plain JavaScript - no React, Angular, or framework needed - and browsers will offer an install prompt, enable push notifications, and cache your app for offline use. The entire setup can be done in under an hour with three files.