Chrome’s built-in device mode is fine until you need to check six breakpoints at once, and then it isn’t. You end up dragging the viewport handle back and forth, re-checking the same page at 360px, 768px, 1024px, and hoping you didn’t miss anything in between.
These five Chrome extensions for responsive testing solve that in different ways. I build one of them (Hoverify), so read that section knowing where I stand. I’ve tried to be fair about the rest, including where they beat us.
- Hoverify: multiple devices side by side with synced clicks, scrolls, and form inputs. Paid, part of a larger toolkit.
- Responsive Viewer: free side-by-side screens with synced scrolling.
- Window Resizer: resizes your actual browser window to exact dimensions.
- Mobile Simulator: mimics mobile behavior like gestures and on-screen keyboards.
- Viewport Resizer: quick viewport presets with custom profiles.
If you’d rather not install anything, Chrome’s own device toolbar covers the basics. We wrote a separate guide to responsive design mode in Chrome if that’s all you need.
1. Hoverify
Hoverify’s Responsive Viewer renders your site on multiple devices at the same time, in one window. Click a link on one device and every device follows. Scroll one, they all scroll. Since the 4.8 update it also syncs form inputs, so you can type into a checkout field once and watch how the layout holds up on every screen size at once.
A few things that came out of real testing pain:
The device list stays current. iPhone 15 and 16 lineups, Pixel 7 Pro, Nothing Phone, plus custom profiles for anything else. You can set device frame styles and colors if you’re screenshotting for a client, and capture the viewport of any single device without leaving the tool.
It can also inject itself directly into the page you’re testing. That matters more than it sounds: purely iframe-based testers break on sites that send X-Frame-Options or frame-blocking CSP headers, which includes a lot of production sites, and injection is how Hoverify opens those anyway. It also removes the headers that give away device emulation, so sites that serve different markup to “mobile” visitors behave the way they actually would on a phone.
And because it’s an all-in-one extension, the Inspector is right there when a breakpoint looks wrong. Hover an element, see its CSS and media queries, edit them live, and re-check every device in the same view. When I’m debugging a layout issue, that loop (spot it, inspect it, fix it, verify everywhere) staying inside one tool is the whole point. There’s a longer walkthrough in our guide to debugging responsive design issues in under 5 minutes.
The honest trade-off: Hoverify is paid. A Solo license is $30/year (or $89 lifetime) and covers three browsers, with a 14-day refund policy but no free trial. If all you need is synced scrolling on a couple of viewports, a free tool below will do. If you also inspect, capture screenshots, extract assets, or audit SEO, one extension replacing five is the pitch. See what else is included.
2. Responsive Viewer
Responsive Viewer is the best free option in this list. It shows multiple screens side by side and syncs scrolling and clicks between them, which covers the core of multi-device testing.
You get preset device profiles and can add custom ones for common resolutions: 360×640 for small phones, 768×1024 for tablets, 1366×768 and 1920×1080 for laptops and desktops. Screens can be arranged and zoomed to fit your monitor.
Where it struggles is the iframe problem mentioned above. Sites that block framing simply won’t load, and there’s no fix from the extension’s side. Input syncing is also more limited than clicking and scrolling. For checking a blog theme or a marketing page across breakpoints, though, it’s hard to argue with free.
3. Window Resizer
Window Resizer takes a different approach: instead of simulating devices, it resizes your real browser window to exact pixel dimensions. One click snaps the window to 375×667, 1024×768, 1920×1080, or any custom size you save.
Because nothing is emulated, what you see is exactly what Chrome renders at that size. That makes it the most “honest” tool here for pure breakpoint work, and the viewport readout is genuinely useful when you’re pinpointing where a media query kicks in.
The limitation is obvious: one size at a time, no device pixel ratios, no touch simulation, no user agent changes. It’s a precision tool for CSS breakpoints, not a device lab. I keep it in the same mental bucket as the breakpoint values guide: useful when you’re deciding where your layout should bend, not for full-site testing.
4. Mobile Simulator
Mobile Simulator focuses on how mobile devices behave rather than just how big they are. It simulates touch gestures (swipe, pinch-to-zoom, tap), screen orientation switching, on-screen keyboard interactions, and device pixel ratios, inside a phone-shaped frame on your desktop.
Its toolbar covers popular devices like the iPhone 13 (390×844), Galaxy S21 (360×800), and iPad Pro (834×1194), and it can throttle network speed to see how the page feels on a slow connection. The touch event debugger, which visualizes touch points and gesture paths, is the standout: if a carousel or drawer only misbehaves under real swipes, this is the cheapest way to catch it before pulling out an actual phone.
It’s one device at a time, and emulated behavior is still emulation. Treat it as a complement to real-device spot checks, not a replacement. Our guide to testing responsive websites across devices covers where emulators end and real devices begin.
5. Viewport Resizer
Viewport Resizer sits between Window Resizer and Responsive Viewer: quick viewport presets, custom device profiles, and a simple toolbar for stepping through screen sizes. It’s a lighter tool than the others and that’s its appeal. Install it, click through your saved sizes, done.
If your testing routine is “check the same four widths on every deploy,” this gets you there with the least ceremony. For synced multi-device previews or mobile behavior simulation you’ll outgrow it quickly.
Which one should you install?
| Tool | Price | Multi-device at once | Synced interactions | Works on frame-blocking sites | Extras |
|---|---|---|---|---|---|
| Hoverify | $30/yr | Yes | Clicks, scrolls, inputs | Yes | Inspector, screenshots, assets, SEO audit |
| Responsive Viewer | Free | Yes | Clicks, scrolls | No | – |
| Window Resizer | Free | No | – | Yes (real window) | Exact pixel resizing |
| Mobile Simulator | Freemium | No | – | Varies | Gestures, keyboard, throttling |
| Viewport Resizer | Free | No | – | Varies | Quick presets |
My honest recommendation: start with Responsive Viewer if you’ve never used a multi-device tester and see whether the workflow sticks. Add Window Resizer if you do a lot of fine breakpoint work. If you find yourself wanting the preview, the inspector, and screenshots in one place, or you keep hitting sites that refuse to load in an iframe, that’s the point where Hoverify earns its price.
Whichever you pick, test with real content and real interactions, not just a resized homepage. Most responsive bugs hide in forms, navigation, and third-party embeds, exactly the places a quick visual scan misses.
