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How to test whether a website is responsive
Do not rely on a single phone preset. Start with the site’s normal desktop presentation, reduce the viewport width in steps, and inspect the layout around each point where it changes or starts to fail. Continue to a narrow viewport condition: WCAG 2.1 Success Criterion 1.4.10 Reflow uses an equivalent width of 320 CSS pixels for vertically scrolling content. Content that intrinsically needs two-dimensional presentation, such as a data table or map, may be an exception; unrelated page content still needs to reflow. W3C guidance on Reflow explains the criterion and exceptions.
- Set up a viewport sweep. Use browser developer tools’ responsive view or automated browser contexts. Shrink gradually from the normal desktop layout rather than checking only named device presets. The DWP Accessibility Manual describes using Chrome DevTools and scaling down to 320 pixels; steps may differ in other browsers.
- Find overflow and lost content. Look for page-wide horizontal scrolling, cut-off text, overlapping controls, fixed-size media, and content that disappears or becomes inaccessible after a breakpoint. Identify the element that extends beyond the page rather than masking the symptom.
- Test zoom and text settings. Increase browser zoom and font settings, including checking text at 200%. Inspect navigation, labels, form controls, and body content for clipping or overlap. The DWP manual recommends checking text scaling, and W3C explains the relationship between reflow and text enlargement.
- Check portrait and landscape. Confirm the page remains usable in both orientations and is not unnecessarily locked to one.
- Test interaction and focus. At each meaningful layout change, navigate with the keyboard. Confirm navigation remains reachable, focus order is understandable, and sticky or fixed content does not obscure the focused element or reading area. Google’s accessible responsive design guidance recommends tabbing through content at each breakpoint.
- Use a physical device for device-dependent questions. Emulation is useful for configured viewport and pointer inputs, but a real phone can help assess actual browser builds, on-screen keyboard behavior, thumb reach, performance feel, and legibility in physical conditions.
Common responsive failures and how to fix them
| Failure | What to inspect | Fix direction |
|---|---|---|
| Page-wide horizontal scrollbar | At narrow widths, identify fixed-width elements, wide images or video, overflowing grid or flex children, tables, and long unbroken strings. | Let ordinary content reflow. Constrain media to its container where appropriate and allow long strings to wrap. If a table or map requires two-dimensional interaction, keep scrolling local to that component rather than the whole page. |
| Text overlaps or is clipped | Increase zoom and text settings; check labels, navigation, controls, and content at narrow widths. | Use flexible sizing and relative units where appropriate, permit wrapping, and adapt the layout as space narrows. |
| Content vanishes after a breakpoint | Compare what remains visible and operable before and after the layout transition. | Preserve access to information and functionality when rearranging or collapsing content. Provide an operable navigation mechanism rather than simply hiding content. |
| Sticky header, footer, or overlay blocks reading or focus | Narrow the viewport or zoom, then navigate by keyboard. Check whether fixed content covers the focused element or takes up too much of the reading area. | At narrow layouts, make sticky elements static, smaller, or user-toggleable. Keep focus visible and ensure covered content can still be reached. |
| Visual order differs from keyboard order | Tab through after changing visual arrangement with Grid or Flexbox. | Keep a logical source order, or ensure the new visual layout still has a coherent focus sequence. |
| A device preset passes but actual use fails | Determine whether the issue depends on a real browser build, physical reach, an on-screen keyboard, performance, or lighting. | Keep repeatable automated viewport checks and supplement them with exploratory checks on relevant real hardware. |
What the 320-pixel reflow check means
WCAG 2.1 Success Criterion 1.4.10 is intended to let users enlarge content without losing information or functionality or needing two-dimensional scrolling for ordinary vertically scrolling content. Its width reference is 320 CSS pixels. For content that scrolls horizontally, the criterion uses an equivalent height of 256 CSS pixels. Content that requires two-dimensional layout for its use or meaning, such as a data table or map, can be treated differently; keep that exception limited to the component that needs it. These are standards thresholds, not performance statistics. See W3C’s Understanding Reflow for details and examples.
A 200% text-enlargement check is also useful: it exposes layouts that assume text cannot grow. It complements rather than replaces narrow-viewport testing, because zoom, user font settings, and viewport changes can reveal different problems.
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Emulation and real-device testing: use both for different questions
| Method | Useful for | What it cannot settle by itself |
|---|---|---|
| Viewport emulation and automation | Repeatable comparisons across widths, checking layout responses, and adding overflow or layout assertions to regression tests. | Physical reach, actual device browser behavior, keyboard overlays, outdoor legibility, and the subjective feel of performance. |
| Manual checks on real hardware | Touch ergonomics, on-screen keyboard behavior, specific browser builds, performance feel, and legibility in real conditions. | Consistent coverage of many widths and repeatable regression checks without a defined test procedure. |
Robot Framework Browser’s documentation distinguishes layout emulation from human checks on real devices. These approaches complement one another: use emulation for repeatable layout behavior, then choose relevant hardware checks for questions that depend on the device or person using it.
Or skip the browser setup
ScreenshotNeo is a website screenshot API and MCP server. Its screenshot output can help you inspect a page at a requested viewport, but an image alone cannot verify keyboard focus order, touch reach, or real-device behavior. One GET request returns an image or PDF:
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpSee the ScreenshotNeo API documentation for request options. Before capture, it can accept cookie or consent banners like a visitor and remove more than 60 known consent platforms, newsletter popups, and chat widgets; each step can be turned off. Bot checks or CAPTCHAs, blank pages, timeouts, failed loads, and cache hits are not billed, and responses identify the page verdict and billing status in headers. Its MCP server offers take_screenshot, get_page_info, and capture_pdf for Claude, Cursor, and other MCP clients. The free plan includes 1,000 screenshots per month with no card; paid plans start at $5 for 3,000.
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Troubleshooting responsive checks
The page scrolls sideways, but the cause is not obvious
Inspect elements at the failing width and look for fixed widths, wide media, grid or flex children that refuse to shrink, tables, and unbroken text. Correct the element or contain necessary two-dimensional scrolling locally; do not hide page overflow as a substitute for finding the cause.
The layout looks fine, but keyboard use is confusing
Tab through after each visual rearrangement. CSS Grid or Flexbox can change where content appears without changing source order. Keep source and focus sequences coherent, and ensure focus remains visible around fixed elements.
Text or controls break only after zooming
Repeat the check with browser zoom and increased text settings. Allow labels and content to wrap, use flexible dimensions where suitable, and adapt control layout rather than clipping the enlarged text.
Automation passes, but users still report problems
Establish whether the failure depends on touch reach, the on-screen keyboard, a particular browser build, physical lighting, or performance feel. Those are reasons to add manual checks on relevant hardware; viewport emulation only confirms the configured inputs it represents.
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Frequently Asked Questions
Does a responsive test require a specific commercial device-testing service?
No. Viewport emulation and automation can cover repeatable layout behavior, while manual checks on relevant real hardware address device-dependent behavior.
Is horizontal scrolling always a responsive design failure?
No. A data table or map may need two-dimensional scrolling. The key is to keep that behavior local to the component rather than forcing unrelated page content to scroll sideways.
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