responsively-org/responsively-app

Responsively App is a desktop browser built specifically for web developers who need to test how their websites look across different screen sizes, phones, tablets, laptops, and desktops, all at the same time. Normally, testing responsive design (designing websites that adapt to different screen widths) means repeatedly resizing your browser window or using browser developer tools to simulate different devices one at a time. Responsively shows multiple device previews simultaneously in a single window. The key feature is mirrored interactions: when you click, scroll, or type in one device preview, all the others do the same thing simultaneously, so you can test a user flow across all screen sizes without repeating every action multiple times. It comes with 30+ built-in device profiles (iPhone, iPad, various Android phones, etc.) and lets you add custom ones. There's a shared element inspector across all devices, one-click screenshots of all previews at once, and hot reloading (the page updates automatically as you change your code). A companion browser extension for Chrome, Firefox, and Edge lets you send URLs from your regular browser directly to the app. You'd use this during front-end web development whenever you need to ensure a page or component looks right on multiple screen sizes. It's free, built with Electron (a framework for building desktop apps with web technologies), and available for Mac, Windows, and Linux.