Best responsive testing tools for your workflow

Fact-checked 14 September 2026

Choose a responsive testing tool around the work you repeat: checking a width, comparing several layouts, or debugging a whole application.

If you only need to check a mobile layout occasionally, start with Chrome DevTools. If you keep resizing the same page after every CSS change, side-by-side viewports can make that loop much shorter. Responsive Tester puts those viewports in Chrome; Responsively App and Sizzy offer separate applications.

Published by Responsive Tester. This comparison describes documented capabilities and practical use cases, not an independent benchmark.

Choose by workflow

OUR PICK

Responsive Tester: work inside Chrome

Responsive Tester opens a page in several viewports on one canvas. Set custom dimensions, save viewport sets as workspaces, and use scroll sync to compare the same area at different widths. Site Breakpoints can build viewports from supported min-width and max-width media queries in the page's accessible stylesheets.

The distinction becomes useful when you edit. Select an element, change a CSS declaration, and compare the result across the open viewports. A declaration inside a media query still follows that query's condition, so you can check a tablet change while keeping the phone and desktop layouts visible.

Viewport management, scroll sync, breakpoint detection, overflow warnings, and screenshots are free. Interaction sync, inspection, live CSS editing, and MCP access are Pro features, included in the seven-day trial. See the Free and Pro comparison for the current terms.

Choose it when the repeated task is reviewing and refining responsive layouts in Chrome. Keep your normal debugging tools available for JavaScript, network requests, and performance analysis. Start with the setup guide or the breakpoint editing walkthrough.

Chrome DevTools: inspect one width closely

Chrome's built-in Device Mode lets you enter an exact viewport size, choose device presets, and display media-query breakpoints. It also provides CPU and network throttling. The Elements panel is useful when you need to understand a declaration in the context of the DOM and the CSS cascade.

Choose DevTools for focused debugging, especially if you are already working in its console or network panel. For visual comparisons across several widths, you will usually resize the preview and repeat the check. Chrome's Device Mode documentation covers the available controls.

Responsively App: a free desktop workspace

Responsively App is free and open source. It shows multiple device views together, mirrors clicks, scrolling, and navigation, and includes a unified inspector and screenshot tools. Device profiles and saved combinations help you return to a familiar set of widths.

It is a useful option if you want a dedicated responsive workspace and are comfortable opening a separate application. Its main download is an app, so consider that difference if you specifically need a Chrome extension. See the official feature overview.

Sizzy: a broader development workspace

Sizzy is a paid developer browser built around side-by-side device previews. Its documented features include synced interactions, project workspaces, isolated sessions, and a debugging panel. Those session controls are relevant when you need to compare different signed-in users as well as different widths.

Consider it if you want more of your development workflow in a dedicated browser. If you mainly need to check a few layouts in your existing Chrome session, that broader workspace may be more than you need. Review Sizzy's current features and plans before choosing.

Compare tools on your own page

Use the same small task in each tool: open a narrow phone width and a desktop width, expand a menu, visit a long content section, and change one CSS value. Check whether the setup and repeated actions feel straightforward on your actual application.

• Can you enter the exact width where your layout breaks?
• Can you compare the same content and UI state across viewports?
• Can you inspect the rule responsible for the difference?
• Can you keep the change in your source code after experimenting?

A viewport preview is only one part of testing. Several widths rendered in Chrome do not test Safari or Firefox, and a desktop preview does not reproduce a phone's hardware or software keyboard. Finish important flows on the browsers and devices your audience uses.

For a repeatable review, use the responsive testing checklist.