seo-rendering

name	seo-rendering
description	Audit a page's rendering strategy and JavaScript dependency — diff raw HTML against the rendered DOM to measure how much primary content, links, headings, and JSON-LD exist only after JS executes, classify CSR-only / SSR / SSG / ISR, and emit framework-specific guidance. Module M4. Feeds both the Search SEO and AI Visibility scores.
allowed-tools	Read, Grep, Glob, WebFetch, Bash

seo-rendering (M4)

Most AI crawlers do not execute JavaScript, so content that only exists after hydration is invisible to them — CSR-only is a hard AI gate. JS dependency also delays first paint; see references/cwv-thresholds.md for how this feeds LCP/INP.

Audits

Working from the PageSnapshot (rendered_dom if present, else raw_html) and the raw HTML the server first returned:

1. Content delta: diff raw_html vs rendered_dom — measure the share of primary text, internal links, headings (h1–h3), and <script type="application/ld+json"> blocks that appear only after JavaScript runs.
2. Classify the strategy: CSR-only (empty/near-empty raw shell, content injected client-side) / SSR / SSG (prerendered static) / ISR (prerendered + revalidated). Use raw-HTML completeness and framework signals (__NEXT_DATA__, hydration markers, data-reactroot, build manifests).
3. Hydration-blocked text: primary content present in raw HTML but hidden/empty until hydration, or rendered only into a client-only island.
4. Lazy-loaded main content: above-the-fold or primary content that requires scroll/intersection/interaction to load — invisible to a non-interacting crawler.
5. AI gate: if the h1, primary body, or JSON-LD exist only in rendered_dom, flag the page as not reliably consumable by non-JS AI crawlers.

Fixes (fixable: advisory)

Rendering strategy is a framework/architecture decision with high breakage risk, so M4 is ADVISORY only — it diagnoses and prioritizes, it never auto-edits build/server code.

• Emit framework-specific guidance: e.g. move CSR-only routes to SSG/ISR or SSR (Next.js App Router server components / generateStaticParams + revalidate; Nuxt/Astro/SvelteKit equivalents).
• Recommend prerendering or partial prerendering for primary content; reserve client-only islands for genuinely interactive widgets.
• Where the right strategy depends on data freshness or constraints the snapshot can't reveal, leave a clearly-marked TODO for the user — never fabricate a revalidate interval or assert a strategy choice. Every finding carries fixable: advisory.

Verification

• render_diff: compute the content-delta ratio of raw_html vs rendered_dom (primary text / links / headings / JSON-LD present in rendered but absent in raw). A high delta on primary content confirms the JS dependency.
• Rendering an accurate rendered_dom requires a headless-browser data tier. When that tier is unavailable, status is needs_api — never a false pass.

Findings

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

• M4.render.csr_only_primary_content — h1 and body text exist only in rendered_dom, raw HTML is an empty shell (status fail, severity 5, axis both, fixable: advisory, confidence established).
• M4.render.jsonld_js_injected — JSON-LD blocks present only after hydration, so non-JS crawlers see no structured data (status warn, severity 4, axis ai, fixable: advisory, confidence established).
• M4.render.lazy_main_content — primary content loads only on scroll/interaction (status warn, severity 4, axis both, fixable: advisory, confidence directional). Each finding: evidence.observed quotes the raw vs rendered delta on the page; verification.reproduce is a runnable render_diff assertion; expected_impact is banded + confidence-tagged (no naked %).

Honesty

• Googlebot does render JavaScript (second-wave, queued), so a well-built CSR app can still rank in classic Search — frame CSR-only as an AI-visibility and crawl-efficiency problem, not an automatic Google-ranking failure.
• Don't claim "SSR ranks higher than CSR" as a ranking factor; the documented effect is content availability to non-JS consumers and faster paint, not a rendering-mode boost. Keep CSR if the page is interactive-by-nature and primary content is still server-delivered.