Mobile audit rules: viewport, tap targets and font size

Audit rules for phones: the viewport tag, pinch zoom, font size, tap targets, sideways scrolling, iOS input zoom, interstitials and the web app manifest.

Mobile rules check whether a page works on a phone: the viewport tag that decides how it is laid out, whether zoom is still available, whether text and tap targets are large enough, and whether anything overflows the screen. Most of them read static markup, so they see inline styles and not the stylesheet, and several report a count as context rather than a measurement. Treat them as a list of things to look at in a narrow browser window.

Run only these rules

squirrel audit https://example.com --rule-include mobile

Where to start

These carry the highest severity and weight in the category.

Missing viewport meta tag: what it does and what to set: Without a viewport meta tag a phone renders the page at desktop width and zooms out. squirrel checks the tag and its content properties.
user-scalable=no: the viewport setting that blocks zoom: Disabling pinch zoom stops readers who need to magnify text. squirrel checks the viewport content for user-scalable and maximum-scale.
Web app manifest: the file that sets the home-screen icon and name: A linked web app manifest that is missing, broken or inconsistent gives a blank home-screen icon and a generic name. squirrel checks the manifest the pages link.
Horizontal scroll on mobile: the usual causes: A page a phone can scroll sideways is a page that does not fit. squirrel looks for fixed widths, tables and fixed-width iframes.
Intrusive interstitials: popups that cover mobile content: A popup covering the content a visitor came for is a ranking problem as well as a usability one. squirrel detects popup markup and libraries.

Rules

Rule	What it flags	Severity	Scope
Font size under 12px: text too small to read on a phone	Body text below about 16px is hard to read on a phone without zooming. squirrel checks inline styles for sizes under 12px.	warning	Per-page
Form fields under 16px: why iOS Safari zooms in when one is focused	On an iPhone, focusing a text field under 16px zooms the page in. squirrel reads form field sizes from inline styles and style blocks and reports the small ones.	warning	Per-page
Horizontal scroll on mobile: the usual causes	A page a phone can scroll sideways is a page that does not fit. squirrel looks for fixed widths, tables and fixed-width iframes.	warning	Per-page
Intrusive interstitials: popups that cover mobile content	A popup covering the content a visitor came for is a ranking problem as well as a usability one. squirrel detects popup markup and libraries.	warning	Per-page
Missing viewport meta tag: what it does and what to set	Without a viewport meta tag a phone renders the page at desktop width and zooms out. squirrel checks the tag and its content properties.	error	Per-page
Tap target size: the 44 by 44 pixel guideline	A control smaller than a fingertip is a control people miss. squirrel counts interactive elements and flags small inline dimensions.	warning	Per-page
user-scalable=no: the viewport setting that blocks zoom	Disabling pinch zoom stops readers who need to magnify text. squirrel checks the viewport content for user-scalable and maximum-scale.	error	Per-page
Web app manifest: the file that sets the home-screen icon and name	A linked web app manifest that is missing, broken or inconsistent gives a blank home-screen icon and a generic name. squirrel checks the manifest the pages link.	error	Site-wide

Key terms

Mobile-friendly: A page that works on a phone without zooming or sideways scrolling: viewport set, readable text, tappable controls, no input zoom.
Touch target size: The tappable area of a control; WCAG 2.2 sets 24 by 24 CSS pixels as the AA minimum.
Viewport meta tag: <meta name="viewport"> that sets the layout width to the device width; disabling zoom in it fails accessibility.

Accessibility checks touch target size and a viewport that blocks zoom from the side of a reader who needs to enlarge text.

Learn more

Fix SEO issues with AI, the coding agent workflow for working through a report
Website audit tool
Sample report, with the Mobile section on a real site

Disable all Mobile rules

[rules]
disable = ["mobile/*"]

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