seo-mobile (M7b)

Google indexes mobile-first: the mobile rendering of a page is the canonical one for ranking. This module checks that a page is usable on a small viewport. Layout problems that hurt mobile usability often surface as CLS — cross-check references/cwv-thresholds.md.

Audits

Working from the PageSnapshot (rendered_dom if present, else raw_html):

Viewport meta: a <meta name="viewport"> exists with width=device-width and initial-scale=1. Flag missing, fixed-width (width=1024), or zoom-blocking (user-scalable=no, maximum-scale=1) values — the last also harms accessibility.
No horizontal scroll: detect fixed-width containers / large absolute widths that force the viewport wider than the device (content overflowing a ~360 px small viewport).
Tap-target size: interactive elements (links, buttons, form controls) should be large enough and spaced so adjacent targets are not easily mis-tapped.
Legible base font: body text rendered at a readable base size, not a desktop-only small size that forces pinch-zoom on mobile.
Content parity: the mobile DOM must contain the same primary content, headings, structured data, and links as desktop — mobile-first indexing ranks what is in the mobile render, so hidden/stripped mobile content is a ranking risk.

Fixes

AUTO (fixable: auto): inject <meta name="viewport" content="width=device-width, initial-scale=1"> into <head> when absent. Deterministic, additive, verifiable — emitted as a diff for fix.
ADVISORY (fixable: advisory): fixed-width/overflow layouts, tap-target sizing, base-font, and parity gaps depend on CSS, design system, and JS — high breakage risk. The tool diagnoses and prioritizes but does not auto-edit layout code. Never invent breakpoint values or pixel sizes — report observed values or leave a clearly-marked TODO for the user.