The 12 tools at a glance
Type, price and what each one does for you. Click a name for the details.
| Tool | Type | Price | Real devices | Finds bugs for you |
|---|---|---|---|---|
| UICheck | Automatic responsive checker (in the cloud) | Free: 5 checks a day. Lens $5/mo, Prism $50/mo | — | |
| Chrome DevTools device mode | Built into Chrome | Free | — | — |
| Firefox Responsive Design Mode | Built into Firefox | Free | — | — |
| Safari Responsive Design Mode | Built into Safari on the Mac | Free | — | — |
| Responsive Viewer | Chrome extension | Free | — | — |
| Am I Responsive | Website | Free | — | — |
| Responsinator | Website | Free | — | — |
| Responsively App | Free desktop browser (open source) | Free and open source | — | — |
| Polypane | Developer browser (desktop) | Paid, with a free trial | — | — |
| Sizzy | Developer browser (desktop) | Paid | — | — |
| BrowserStack | Real device cloud | Paid, with a free trial | — | |
| LambdaTest (TestMu AI) | Browser and device cloud | Free plan with limited use; paid plans | — |
The tools in detail
01
UICheck
Automatic responsive checker (in the cloud)
Paste a URL and UICheck opens the page at every screen size in real browser engines, then lists what is broken: sideways scrolling, cut-off text, overlaps, small tap targets, broken images, forms and accessibility, each on a screenshot with the fix.
- Best for
- Finding every layout bug on every page before launch
- Price
- Free: 5 checks a day. Lens $5/mo, Prism $50/mo
- Runs on
- Any browser, nothing to install; CLI for CI
- Browser engines
- Chrome, Safari (WebKit) and Firefox
Key features
- Every screen size from one URL
- Bugs listed with screenshot and fix
- Breakpoint sweep 320–1920px
- Whole-site checks
- Figma comparison
- Visual baselines
- PDF and Excel reports
- CI and AI assistant (MCP)
Good
- +Finds and explains problems, so nobody clicks through devices
- +Safari’s engine without a Mac
- +Works on staging sites behind a login
Watch out
- –Real browser engines at exact sizes, not physical phones
- –The free plan checks one page at a time on 5 sizes
02
Chrome DevTools device mode
Built into Chrome
Press Ctrl+Shift+M (Cmd+Shift+M on a Mac) in DevTools to see the page at a phone or tablet size, with touch and device pixel ratio emulated. It is where most developers start.
- Best for
- Quick checks while writing CSS
- Price
- Free
- Runs on
- Chrome on Windows, macOS and Linux
- Browser engines
- Chromium only
Key features
- Device presets and custom sizes
- Touch and pixel ratio emulation
- Network and CPU throttling
- Media query bar
- Full-page screenshots
Good
- +Already installed and instant
- +Inspect and edit the CSS live
Watch out
- –One size at a time
- –Chrome’s engine only, so Safari bugs don’t show
- –You have to find the problems yourself
03
Firefox Responsive Design Mode
Built into Firefox
Firefox’s own device mode (Ctrl+Shift+M): device presets, custom sizes, touch simulation and throttling, rendered by Firefox’s engine.
- Best for
- Checking layouts in Firefox’s engine
- Price
- Free
- Runs on
- Firefox on Windows, macOS and Linux
- Browser engines
- Gecko (Firefox)
Key features
- Device presets and custom sizes
- Touch simulation
- Network throttling
- Viewport screenshots
Good
- +Free and built in
- +Shows Firefox-specific layout differences
Watch out
- –One size at a time
- –Firefox only
04
Safari Responsive Design Mode
Built into Safari on the Mac
Turn on the Develop menu in Safari’s settings, then choose Enter Responsive Design Mode to see the page at iPhone and iPad sizes in WebKit.
- Best for
- Checking WebKit, the engine on every iPhone
- Price
- Free
- Runs on
- Safari on macOS
- Browser engines
- WebKit (Safari)
Key features
- iPhone and iPad presets
- Custom sizes
- User agent switching
- Web Inspector
Good
- +The engine iPhones use
- +Free
Watch out
- –Needs a Mac
- –Desktop Safari, so some iPhone-only behaviour (address bar, keyboard) differs
05
Responsive Viewer
Chrome extension
Shows the current page at several screen sizes in one view, with scrolling and clicks kept in sync, so you can watch layouts change while you work.
- Best for
- Seeing several sizes of the page you are on
- Price
- Free
- Runs on
- Chrome and Chromium browsers
- Browser engines
- Chromium
Key features
- Several sizes in one view
- Synced scrolling and clicks
- Screenshots
Good
- +Free and quick to install
- +Many sizes at once
Watch out
- –Loads pages in frames, which some sites and logins block
- –Chromium only
- –You do the looking
06
Am I Responsive
Website
Enter a URL and see it in four device frames at once: a desktop, a laptop, a tablet and a phone. It is made for presentation images rather than testing.
- Best for
- A quick device mockup image for a portfolio or pitch
- Price
- Free
- Runs on
- Any browser
- Browser engines
- Your own browser
Key features
- Four device frames from one URL
- Handy for screenshots and pitches
Good
- +Instant, nothing to install
- +Good-looking image for a presentation
Watch out
- –Four fixed sizes
- –Uses frames, so many sites refuse to load
- –Not built for finding bugs
07
Responsinator
Website
Shows your site in a list of phone and tablet frames, upright and sideways, from a single URL.
- Best for
- A fast look at common phone and tablet sizes
- Price
- Free
- Runs on
- Any browser
- Browser engines
- Your own browser
Key features
- Common phone and tablet frames
- Portrait and landscape
Good
- +Free and instant
Watch out
- –Uses frames, which many sites block
- –Device list can lag behind new phones
- –No bug finding
08
Responsively App
Free desktop browser (open source)
A desktop app that shows your site on many devices at once and mirrors clicks, scrolling and typing across all of them, with hot reload while you code.
- Best for
- Free side-by-side development
- Price
- Free and open source
- Runs on
- macOS, Windows and Linux
- Browser engines
- Chromium
Key features
- Many devices side by side
- Mirrored clicks, scroll and typing
- Hot reload
- Element inspector
- Screenshots of every device
Good
- +Free and open source
- +Great while building
Watch out
- –Chromium only
- –A desktop app to install
- –You spot problems by eye
09
Polypane
Developer browser (desktop)
A browser built for web development: synced panes at any sizes, plus accessibility and SEO checks, contrast and colour-blindness overlays and live CSS editing.
- Best for
- Front-end developers building responsive layouts every day
- Price
- Paid, with a free trial
- Runs on
- macOS, Windows and Linux
- Browser engines
- Chromium
Key features
- Synced panes at any sizes
- Breakpoints suggested from your CSS
- Accessibility and SEO checks
- Contrast and colour-blindness overlays
- Live CSS editing
Good
- +Very complete for front-end work
- +Accessibility tools built in
Watch out
- –Paid
- –Chromium panes only
- –Made for developers, not for client reports
10
Sizzy
Developer browser (desktop)
A paid desktop browser that keeps many devices side by side with scrolling and clicks in sync, plus tools for building and debugging responsive layouts.
- Best for
- Developers who want many devices in sync while coding
- Price
- Paid
- Runs on
- macOS, Windows and Linux
- Browser engines
- Chromium
Key features
- Many devices side by side
- Synced scrolling and clicks
- Screenshots
- Dev tools per device
Good
- +Fast workflow for building layouts
Watch out
- –Paid
- –Chromium only
- –You spot problems by eye
11
BrowserStack
Real device cloud
Thousands of real phones, tablets and browsers to test by hand (Live) or with automated scripts (Automate). Visual testing (Percy) and accessibility testing are separate products.
- Best for
- Testing on real phones and many browser versions
- Price
- Paid, with a free trial
- Runs on
- In the browser; real iOS and Android devices in the cloud
- Browser engines
- Real Safari, Chrome, Firefox and Edge on real devices
Key features
- Thousands of real devices and browsers
- Live manual testing
- Automated tests (Selenium, Playwright, Cypress)
- Testing local and staging sites
Good
- +Real devices: touch, device fonts, payment sheets
- +Every browser version you could need
Watch out
- –You test by hand or write scripts
- –Priced for QA teams
- –Slow to cover many pages at many sizes
12
LambdaTest (TestMu AI)
Browser and device cloud
A cloud of browsers and real devices for manual and automated testing, now part of TestMu AI. Its LT Browser desktop app shows a site on several device sizes side by side.
- Best for
- A BrowserStack-style cloud, with a responsive browser included
- Price
- Free plan with limited use; paid plans
- Runs on
- In the browser; LT Browser desktop app
- Browser engines
- Real browsers and devices in the cloud
Key features
- Cloud browsers and real devices
- LT Browser for side-by-side sizes
- Automation grid
- Visual regression
Good
- +Close match to BrowserStack
- +Responsive browser included
Watch out
- –You test by hand or with scripts
- –Many products to learn
01
What to look for in a responsive testing tool
- Safari: every browser on an iPhone uses Safari’s WebKit engine, so a tool that only runs Chrome misses iPhone bugs
- Widths in between: bugs hide at 700px or 900px, not only at named devices, so check whether you can sweep sizes
- Finding vs showing: viewers show you the page and you spot problems; checkers find and list them
- Every page: a tool that checks one page at a time takes hours on a 50-page site
- Real devices: needed for touch gestures, the on-screen keyboard and payment sheets, not for most layout bugs
- Sharing: a report or link you can hand to a client or developer saves explaining screenshots
- Staging and logins: password-protected and local sites need a tool that can reach them
02
Emulators, real engines and real devices
Device mode in a browser resizes the page and fakes touch, but it is still that browser’s engine: Chrome’s device mode shows Chrome, not Safari. Real-engine tools render the page in Chrome, Safari’s WebKit and Firefox at exact screen sizes, which shows the same layout a phone would. Real-device clouds run the actual phones, which matters for touch, device fonts and hardware, and costs the most time.
03
Which tool for which job
- Quick look while building: Chrome DevTools device mode, or Firefox and Safari’s own modes
- Building CSS every day: Responsively App (free), Polypane or Sizzy
- A device mockup image for a pitch: Am I Responsive
- Every page and size checked before launch, with a report for the client: UICheck
- Touch, payments or many browser versions on real phones: BrowserStack or LambdaTest
04
A workflow that uses three of them
- 1While building: DevTools or a developer browser to see sizes as you write CSS
- 2Before launch: an automatic check of every page at every size, in Chrome, Safari and Firefox
- 3For touch-critical flows such as checkout: one pass on a real phone or a device cloud
Tip: Most layout bugs show up the same in a real browser engine at the exact screen size as on the phone, so save real-device time for the flows where touch and the keyboard matter.
Checklist
Questions
What is the best free responsive design testing tool?
For a quick look, Chrome DevTools device mode. For a list of what is broken at each size, a free automatic checker such as UICheck’s responsive design checker.
Which tool is used for responsive testing?
The most common is Chrome DevTools device mode, built into the browser, for a quick look at one size at a time. Developers also use Polypane, Sizzy or Responsively App, teams that need real phones use BrowserStack or LambdaTest, and an automatic checker such as UICheck tests every screen size and lists the bugs for you.
Is Chrome DevTools enough for responsive testing?
For quick checks while you build, yes. It shows one size at a time and only Chrome’s engine, so it misses Safari bugs and the widths you didn’t try.
How can I test Safari without a Mac?
Use a tool that renders with Safari’s WebKit engine, such as UICheck, or a real-device cloud such as BrowserStack or LambdaTest.
What are the best website QA tools?
A responsive and layout checker, a broken link checker, an accessibility checker, a feedback tool for clients and, for apps with heavy logic, a device cloud. UICheck combines the first four for websites.
Do I need real devices for responsive testing?
Rarely for layout: real browser engines at exact screen sizes show the same layout. Real devices matter for touch gestures, device fonts and hardware features.