Building web applications that look just as intended on a large number of devices and screen sizes can be cumbersome. Sizzy is a SaaS solution that shows many viewports in a single browser window. The application is rendered in all viewports simultaneously and interactions with the application are also synched across the viewports. In our experience interacting with an application in this way can make it easier to spot potential issues earlier, before a visual regression testing tool flags the issue in the build pipeline. We should mention, though, that some of our developers who tried Sizzy for a while did, on balance, prefer to work with the tooling provided by Chrome.