Responsively is a browser built for responsive review: line up any set of viewports side by side and every scroll, click and navigation happens on all of them simultaneously. When an agent claims a layout “works on mobile”, this is the tool that checks five devices in one glance.
Where it shines
- Synchronized everything. Mirrored scroll and input means testing three breakpoints costs the effort of one.
- Design-breakpoint presets. iPhone, Pixel, iPad, ultrawide - save custom device sets per project.
- Built-in utilities. Visual ruler, element inspector across devices and one-click screenshot exports for design review.
Where it falls short
- It previews rendering, not real-device performance; touch latency and network behavior still belong on hardware.
- A separate app to keep updated alongside your daily browser.
The real cost
Free and open source. The only cost is accepting that “it looks fine on my monitor” was never responsive testing.
Verdict
The missing screen for AI-assisted web work: agents generate layouts fast, and Responsively lets you verify them across devices just as fast.
