Polypane: web browser for developers

a tool for fast testing web apps in multiple sizes (desktop, tablet, mobile, etc.)

based on Electron, with Chromium embedded, React for UI

subscription based, free trial

Polypane, The browser for ambitious web developers

Like using DevTools with cheats enabled.
A stand-alone browser and devtool for ambitious web developers that want to build more responsive, accessible and performant sites in less time. Save hours on each project, love every minute of it.

podcast interview with the creator of the tool

Polypane-demonium with Kilian Valkhof, creator of Polypane (JS Party #327)

Understanding Core Web Vitals and Google search results | Google Search Central  |  Documentation  |  Google for Developers