Responsive Simulator - Multi Device Viewport Tester

View your site on mobile, tablet & desktop viewports side by side. Fast responsive web design checker for developers.

Responsive Simulator is a responsive web design checker and multi device viewport tester for developers, designers, and QA teams. View your website on mobile, tablet, and desktop viewports side by side, so you can test layouts faster without constantly resizing your browser. Use Responsive Simulator to preview any webpage across synced viewports. Open a site, click the extension icon, and inspect how the page behaves across common device sizes in one workspace. What you can do with Responsive Simulator: ➤ View mobile, tablet, and desktop layouts side by side ➤ Test responsive web design across multiple viewport sizes ➤ Add custom viewport dimensions in pixels ➤ Use built-in presets for iPhone, Android, iPad, tablet, laptop, desktop, and 4K screens ➤ Switch between column and grid layouts ➤ Rotate individual viewports ➤ Pin important viewports to the front ➤ Expand one viewport to focus on a single screen size ➤ Sync scrolling across viewports ➤ Sync navigation and interactions across viewports ➤ Switch between light and dark page themes when supported ➤ Save viewport configurations and reuse them on other websites ➤ Reset back to the default viewport setup when needed Responsive Simulator is built for everyday frontend work. It helps you check breakpoints, compare layouts, review spacing, test mobile navigation, and catch responsive issues before shipping changes. Instead of opening multiple browser windows or resizing DevTools repeatedly, you can keep all important viewport sizes visible in one clean interface. This makes it easier to compare how a page behaves across screen sizes and spot layout problems quickly. Common use cases: ➤ Testing landing pages on mobile, tablet, and desktop ➤ Checking responsive layouts during frontend development ➤ Reviewing client websites across common device sizes ➤ QA testing before publishing a site update ➤ Comparing mobile and desktop navigation ➤ Testing custom breakpoints ➤ Saving reusable viewport sets for different projects ➤ Inspecting pages that need consistent behavior across devices Responsive Simulator does not change your website. It creates a local multi viewport testing view in your browser so you can preview the current page across different screen sizes. This extension is useful for: ➤ Frontend developers ➤ Web designers ➤ UI designers ➤ QA testers ➤ Indie hackers ➤ Webflow, Framer, WordPress, Shopify, and custom site builders ➤ Anyone who needs to check responsive web design quickly If you build or review websites, Responsive Simulator gives you a simple way to test multiple device viewports at the same time.