Responsively App - A web developer's browser

Overview Responsively App is a free and open-source browser built specifically for web developers who need to build and test responsive websites. It shows all device views side by side at once, eliminating the need to manually resize browser windows or switch between devtools. Unlike using browser developer tools alone, Responsively App mirrors interactions like clicks and scrolls across every device in real time. It targets front-end developers who want faster, more precise responsive testing without buying physical devices or manual resizing. Key Benefits View all device previews simultaneously in a single window for instant visual comparison. Any click, scroll, or navigation performed on one device replicates automatically across all open devices in real time. Save favorite device combinations as Preview Suits and switch between them instantly during testing. Comes with a large collection of pre-configured device profiles and supports adding custom devices. Inspect elements across all devices at once using the Unified Inspector activated by Cmd/Ctrl + I. Take full-page screenshots of all devices with a single click, or capture individual device screenshots. How It Works You download and launch Responsively App, then enter a website URL. The app displays the site in multiple device viewports side by side automatically. You interact with any single device — clicking, scrolling, or navigating — and the action mirrors to all other devices in real time, letting you spot layout inconsistencies at a glance. Use Cases Front-end web developers testing responsive layouts across phones, tablets, and desktops simultaneously. UI designers verifying pixel-perfect rendering on multiple screen sizes before handing off to engineering. QA engineers performing cross-device regression testing without maintaining a physical device lab. Freelance web developers who need a fast, free tool to validate responsive sites for client projects. Open-source contributors building and verifying responsive web components across form factors. Why Choose This Product Responsively App is best suited for individual developers and small teams who need a free, open-source tool for responsive web testing. It is not a replacement for testing on real physical devices — the page explicitly cautions that it uses the same rendering engine as the browser and recommends real devices for final validation where hardware-specific behavior matters.