/seo-mobile

name: seo-mobile
description: Audit mobile-friendliness of a page from the PageSnapshot — verify the viewport meta, no horizontal-scroll/fixed-width layouts, adequate tap targets, legible base font, and mobile/desktop content parity — and generate the viewport meta when missing. Module M7b. Feeds the Search SEO score.
allowed-tools: Read, Grep, Glob, WebFetch, Bash

<!-- Portions Copyright (c) 2026 Enrique Rocha (@soyenriquerocha) - see LICENSE for original authors · tododeia.com · id er-d03758e1 -->

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`.

Inputs

Work from the PageSnapshot named in your dispatch envelope: read `parsed` from `<run_dir>/pages/<slug>.json` (`metas[]` for the viewport tag) and `parsed_rendered` when `render.used` is not `none` (layout/geometry checks need it); Grep `pages/<slug>.html` for verbatim evidence; site artifacts live in `<run_dir>/site/{robots.json,sitemaps.json,discovery.json}`. Deterministic findings already emitted by `audit.mjs` are listed in `<run_dir>/findings.deterministic.json` — do not re-emit those ids; add model-judged findings only. If invoked directly with a URL/path and no snapshot exists, first run `node "${CLAUDE_PLUGIN_ROOT}/scripts/snapshot.mjs" <target> --out "${CLAUDE_PLUGIN_DATA}/runs"` and use the printed snapshot path.

Audits

Working from the PageSnapshot (`parsed_rendered` when `render.used` is not `none`, else `parsed`): 1. **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. 2. **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). 3. **Tap-target size**: interactive elements (links, buttons, form controls) should be large enough and spaced so adjacent targets are not easily mis-tapped. 4. **Legible base font**: body text rendered at a readable base size, not a desktop-only small size that forces pinch-zoom on mobile. 5. **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.

Verification

• Method `dom_assert`: assert against the snapshot (viewport meta presence/content, computed widths, target geometry).
• Reproduce the deterministic part (viewport meta presence/content) offline: `node "${CLAUDE_PLUGIN_ROOT}/scripts/parse-html.mjs" --snapshot <pages/<slug>.json>` (or `--url <u>` / `--file <path>`) — inspect `head_hygiene.viewport`. Tap-target/overflow geometry is a `manual_review` pass over the rendered snapshot.
• Tap-target and overflow checks need the **rendered** snapshot (computed layout). When only `raw_html_path` is available and layout cannot be resolved, status is `needs_api`, never a false `pass`.

Findings

Emit findings per `schema/finding.schema.json`. Examples:

• `M7b.viewport.missing` — no viewport meta (status `fail`, severity 3, `fixable: auto`, axis `search`, confidence `established`).
• `M7b.viewport.user_scalable_no` — viewport disables zoom (status `warn`, severity 3, `fixable: advisory`, axis `search`, confidence `established`).
• `M7b.layout.horizontal_scroll` — content overflows the small viewport (status `fail`, severity 3, `fixable: advisory`, axis `search`, confidence `directional`).
• `M7b.taptarget.too_small` — interactive targets too small/close (status `warn`, severity 3, `fixable: advisory`, axis `search`, confidence `directional`).

Each finding: `evidence.observed` quotes the page (the meta tag string, the overflowing selector/width, the target geometry); `verification.reproduce` is the runnable command above; `expected_impact` is banded + confidence-tagged (no naked %).

Honesty

• Mobile-friendliness is a usability baseline, not a strong positive ranking lever — a fast, well-built desktop-only site does not get a ranking *boost* for adding a viewport tag; it removes a usability liability. Frame fixes as removing risk, not gaining rank.
• Google retired the standalone "Mobile-Friendly Test" tool and the page-experience badge; there is no single mobile-friendly ranking flag to "win." Don't ship that myth.
• A present viewport meta does not prove the layout is actually responsive — confirm with the rendered snapshot, don't infer responsiveness from the tag alone.