Skip to content
SEO Toolbox Online

Mobile Responsiveness Tester

Checks the viewport tag, tap targets, font size and horizontal scroll together.

Runs a real Chromium page load — usually takes 5–15 seconds.

What this tool checks

  • Responsive viewport meta tag

    Checks for <meta name="viewport" content="width=device-width, initial-scale=1">.

    Why it matters: Without a viewport meta tag, mobile browsers render the page at desktop width and zoom out, making it hard to read and use.

    If it fails: Add <meta name="viewport" content="width=device-width, initial-scale=1"> to <head>.

    Source: developer.mozilla.org/en-US/docs/Web/HTML/Viewport_meta_tag

  • Tap targets are large enough

    Rendered on a 390px-wide mobile viewport, counts interactive elements smaller than 44×44 CSS pixels. Links inside a sentence and visually hidden elements (such as skip links) are excluded, as in WCAG 2.5.5.

    Why it matters: Small or tightly-packed tap targets are hard to hit accurately on a touchscreen, causing mis-taps and frustration.

    If it fails: Make buttons and links at least 44×44px with adequate spacing between them.

    Source: w3.org/WAI/WCAG22/Understanding/target-size-enhanced.html

  • Legible font sizes on mobile

    On the mobile render, checks what share of text uses a computed font size below 12px.

    Why it matters: Text under about 12px forces mobile users to pinch-zoom to read, which is a poor experience.

    If it fails: Use a base font size of at least 16px for body text on mobile.

    Source: web.dev/articles/font-size

  • Content fits the mobile viewport

    Checks the rendered mobile page does not scroll horizontally.

    Why it matters: Horizontal scrolling on mobile usually means an element is wider than the screen — often a fixed-width image, table or container.

    If it fails: Use responsive units and max-width:100% on media; let wide tables scroll inside their own container.

    Source: web.dev/articles/viewport

Related tools