performance-audit

performance-audit is a skill for Claude Code from me2resh/apexyard. It costs 33 tokens per session (1,397 once invoked), scanned A, original, MIT.

A code-based performance review that examines bundle size, image handling, lazy loading, code splitting, caching, and Core Web Vitals, which measure important loading and interaction experiences.

In plain words
What is it for?
Use it to inspect build output, find oversized assets, review loading strategies, and check production performance settings.
Why use it?
It helps locate likely causes of slow pages and layout shifts before or alongside deeper browser testing.

Skill for Claude Code

Written for Claude Code: disable-model-invocation in frontmatter. Also seen: mentions Claude Code.

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/me2resh/apexyard/performance-audit
Any agent
npx skills add me2resh/apexyard --skill performance-audit
Clone the repo
git clone --depth 1 https://github.com/me2resh/apexyard

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for performance-audit

README.md
[![agentmods](https://agentmods.dev/badge/skills/me2resh/apexyard/performance-audit.svg)](https://agentmods.dev/skills/me2resh/apexyard/performance-audit)
Your own site
<a href="https://agentmods.dev/skills/me2resh/apexyard/performance-audit"><img src="https://agentmods.dev/badge/skills/me2resh/apexyard/performance-audit.svg" alt="Measured on agentmods" height="20"></a>
Per session 33 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,397 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00033 $0.01397
Opus 5 $0.00016 $0.00698
Sonnet 5 $0.00007 $0.00279
Haiku 4.5 $0.00003 $0.00140

Measured 2d ago against content hash 0394ada1747b, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

performance-audit scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/skills/performance-audit/SKILL.md · 121 lines

How it starts

The opening of the file, as written. The whole thing — 121 lines — stays where its author put it; the contents beside it link to each section on GitHub.

/performance-audit — Bundle & Core Web Vitals Analysis

Deep-dive performance analysis focused on what's measurable from the codebase without running Lighthouse. Checks bundle size, image optimization, lazy loading, code splitting, and caching configuration. Invoke when /launch-check's performance row shows WARN or FAIL.

Process

Step 1: Bundle analysis

  • Check for build output (dist/, build/, .next/, out/)
  • If build exists: measure total JS + CSS size, identify the 5 largest files
  • Check for code splitting (dynamic imports, React.lazy, next/dynamic, route-based splitting)
  • Check for tree shaking configuration (ES modules, sideEffects: false in package.json)
  • Check if source maps are excluded from production build

Step 2: Image optimization

  • Find all images in the project (src, public, static, assets directories)
  • Check formats: are images served as WebP/AVIF, or only PNG/JPEG?
  • Check for oversized images (> 500KB, > 2000px width)
  • Check for next/image, @astrojs/image, or similar optimization components
  • Check for loading="lazy" on below-the-fold images
  • Check for explicit width and height attributes (prevents layout shift)

Step 3: Loading performance

  • Check for render-blocking resources (CSS in <head> without media, sync <script> without defer/async)
  • Check for font loading strategy (font-display: swap, preloading, self-hosted vs Google Fonts)
  • Check for preconnect/prefetch hints for critical third-party origins
  • Check for service worker or caching configuration

Step 4: API performance (if applicable)

  • Check for N+1 query patterns (multiple sequential fetches that could be batched)
  • Check for pagination on list endpoints
  • Check for caching headers (Cache-Control, ETag)
  • Check for compression middleware (gzip/brotli)

Step 5: Output

PERFORMANCE AUDIT — <project> @ <sha>

| # | Area | Status | Finding |
|----|------|--------|---------|
| P1 | Bundle | WARN | Total JS 420KB gzipped (target: < 300KB). Largest: vendor.js 180KB |
| P2 | Code splitting | PASS | 12 dynamic imports, route-based splitting configured |
| P3 | Images | FAIL | 8 images > 500KB, none in WebP format |
| P4 | Lazy loading | WARN | 4 below-fold images without loading="lazy" |
| P5 | Fonts | PASS | Self-hosted, font-display: swap |
| P6 | Caching | PASS | Cache-Control headers on static assets |

Performance readiness: NEEDS WORK (1 fail, 2 warnings)
Estimated LCP improvement: -1.2s if images are optimized and lazy-loaded

Read the full file on GitHub · 121 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 121 lines · 33 tokens per session scan A 0394ada1747b

Subscribe to this mod's changes

performance-audit is a skill published in the GitHub repository me2resh/apexyard (499 stars, last pushed yesterday), licensed MIT. It adds 33 tokens to every session and 1,397 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.

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