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Seo core web vitals

Skill Hainrixz/claude-seo-ai/skills/seo-core-web-vitals

Audit Core Web Vitals & page performance — measure LCP, INP, and CLS against p75 field thresholds, diagnose render-blocking resources, unoptimized images, and layout-shift sources, and produce prioritized, advisory-only remediation guidance. Module M15. Feeds the Search SEO score (heavily) and the AI Visibility score (minimally).From its SKILL.md

Install
npx -y skills add Hainrixz/claude-seo-ai --skill seo-core-web-vitals

Assembled from the repository path, not quoted from the project. Check it against their README if it does not work.

One thing to look at

  • runs commandsInstructs the agent to run 1 command, including `node ${CLAUDE_SKILL_DIR}/../../scripts/psi-client.mjs --url <u>`.

SKILL.md

4.4 KB, ~1.1k tokens by cl100k_base, as published. Nobody here has run it

seo-core-web-vitals (M15)

Core Web Vitals are a confirmed Google ranking signal and a proxy for page quality. Thresholds, field-vs-lab honesty rules, and LCP decomposition: references/cwv-thresholds.md (follow it exactly).

Audits

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

  1. Field CWV at p75 — LCP ≤ 2.5 s, INP ≤ 200 ms (INP replaced FID), CLS ≤ 0.1, all at the 75th percentile of real-user data. All three must pass for a "good" rating. Use the proactive-warning thresholds (LCP > 2.0 s, INP > 160 ms, CLS > 0.08) to warn before failing.
  2. Render-blocking resources — synchronous <script> in <head> (no defer/async/type=module), blocking <link rel="stylesheet">, and @import chains that delay first render (LCP/INP risk).
  3. Unoptimized images — missing width/height (or aspect-ratio), no loading="lazy" below the fold, no responsive srcset/sizes, legacy formats where AVIF/WebP would serve, and a non-preloaded LCP image.
  4. Layout-shift sources — images/iframes/ads/embeds without reserved dimensions, web-font swap without font-display/size-adjust, and content injected above existing content (CLS risk).
  5. LCP decomposition — attribute LCP to TTFB vs resource load delay vs load duration vs render delay (see references/cwv-thresholds.md) so each finding targets the dominant subpart.

Fixes (fixable: advisory)

Advisory only. Performance fixes touch build config, server, CDN, and runtime JavaScript — high breakage risk — so the tool diagnoses and prioritizes but never auto-edits performance code. For each failing metric, name the specific resource/element causing it and rank fixes by expected leverage (e.g. preload the LCP image, defer non-critical JS, reserve image dimensions). Give framework-specific direction where the stack is known. Never fabricate measured values — if field data is absent, ask the user to supply a PSI/CrUX key or leave a clearly-marked TODO placeholder rather than guessing a metric.

Verification

  • Field (Tier 1): node ${CLAUDE_SKILL_DIR}/../../scripts/psi-client.mjs --url <u> calls the PageSpeed Insights API (loadingExperience, method psi_api); CrUX History via the same client (crux_api) for p75 trends. Requires a free API key.
  • Tier 0 (no key): emit status: needs_api for every field-CWV finding, plus clearly-labeled lab heuristics (render-blocking count, missing image dimensions, bundle weight). Label lab signals "lab data — not what Google ranks on"; never present a heuristic as a measured field value.
  • When the required data tier is unavailable, status is needs_api — never a false pass.

Findings

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

  • M15.lcp.exceeds_p75 — field LCP > 2.5 s at p75 (status fail, severity 4, fixable: advisory, axis search, confidence established). evidence.observed quotes the measured p75 value and the LCP element; verification.reproduce runs the psi-client command.
  • M15.cls.unsized_image — image with no width/height shifting layout (status warn, severity 4, fixable: advisory, axis search, confidence directional). evidence.observed quotes the <img> tag.
  • M15.field.needs_api — no PSI/CrUX key, field CWV unverifiable (status needs_api, severity 4, fixable: advisory, axis search, confidence established). Each finding: evidence.observed quotes the page/measurement; verification.reproduce is the runnable command; expected_impact is banded + confidence-tagged (no naked %).

Honesty

  • Lab ≠ field. A single local Lighthouse run is diagnostic only; Google ranks on field (CrUX) p75. Never let a lab number drive the Search score or masquerade as a field result.
  • CWV is a real but modest tie-breaker signal — it does not override relevance/content quality. Don't promise ranking jumps from a green score; report it as banded expected_impact, not a predicted percentage gain.
  • A "100" lab performance score is not a pass if field p75 fails; only field data settles a CWV finding.

What ships with it

Read from the repository

Just SKILL.md. No reference files, no scripts.

Gives 0 of the 12 instructions most marketing audience skills give in ~1.1k tokens

Counted across 690 of the 894 authors here whose files we hold, read 2026-08-07

  • Apply Poppins font to headingsin 41 of 690, across 6 files
  • Apply Lora font to body textin 41 of 690, across 6 files
  • Use Arial fallback for headingsin 39 of 690, across 4 files
  • Use Georgia fallback for body textin 39 of 690, across 4 files
  • Maintain text hierarchy and formattingin 39 of 690, across 4 files
  • Use accent colors for non-text shapesin 38 of 690, across 3 files
  • Use RGB values for precise color matchingin 38 of 690, across 3 files
  • Use brand colors for primary text and backgroundsin 36 of 690, across 1 file
  • Read product marketing context file before asking questions, starting, or auditingin 35 of 690, across 23 files
  • Use active voice instead of passive voicein 26 of 690, across 10 files
  • Implement or generate appropriate JSON-LD structured datain 24 of 690, across 17 files
  • Prioritize clarity over clevernessin 22 of 690, across 8 files

Said here and by no other author read

  • evaluate p75 field metrics against thresholds
  • issue warnings before metrics fail
  • check head for render-blocking resources
  • check images for missing dimensions
  • check images for missing lazy loading
  • identify layout shift sources

Grouped from the skills themselves: near-identical wordings counted once, and counted by distinct author, so one author publishing three of these counts once. Length counted with cl100k_base; the agent that loads this file may tokenize it differently.

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