performance-analyzer

A skill for examining CSS, the rules that control how web pages look, for loading and rendering problems. It reviews file size, unused rules, selectors, and resources that delay or slow display.

In plain words
What is it for?
Use it to review CSS bundles, find duplicate or unused styles, assess render-blocking resources, and suggest loading or optimization changes.
Why use it?
It helps identify why a page may load slowly or spend unnecessary time calculating and applying styles.

Skill for Claude CodeCodex

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/andronics/claude-plugin-css-pro/performance-analyzer
Any agent
npx skills add andronics/claude-plugin-css-pro --skill performance-analyzer
Clone the repo
git clone --depth 1 https://github.com/andronics/claude-plugin-css-pro

Made for: Claude Code, Codex.

Per session 39 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,512 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 $0.00039 $0.03512
Opus 5 $0.00019 $0.01756
Sonnet 5 $0.00008 $0.00702
Haiku 4.5 $0.00004 $0.00351

Measured 2d ago against content hash 33634e7eddbb, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

performance-analyzer 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.

skills/performance-analyzer/SKILL.md · 597 lines

How it starts

The opening of the file, as written. The whole thing — 597 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Performance Analyzer Skill

This skill analyzes CSS performance and identifies optimization opportunities. I'll examine bundle size, selector efficiency, render performance, and suggest specific improvements to make your CSS faster.

What I Analyze

Bundle Analysis

  • Total CSS file size
  • Unused CSS percentage
  • Duplicate rules
  • Minification potential
  • Compression ratios

Selector Performance

  • Selector complexity
  • Expensive selectors
  • Over-specific rules
  • Selector matching speed

Render Performance

  • Render-blocking CSS
  • Critical CSS opportunities
  • Paint/layout triggers
  • Animation performance

Loading Strategy

  • CSS delivery method
  • Code splitting potential
  • Async loading opportunities
  • Caching strategy

Performance Metrics

Key Indicators

First Contentful Paint (FCP)

  • When first content appears
  • Target: < 1.8s

Largest Contentful Paint (LCP)

  • When main content visible
  • Target: < 2.5s

Cumulative Layout Shift (CLS)

  • Visual stability
  • Target: < 0.1

CSS Bundle Size

  • Total downloaded CSS
  • Target: < 50KB gzipped for initial load

Unused CSS

  • Percentage not used on page
  • Target: < 20% unused

Bundle Size Analysis

File Size Audit

# Check CSS file sizes
ls -lh dist/*.css

# Example output:
# styles.css        250KB (uncompressed)
# styles.min.css    180KB (minified)
# styles.min.css.gz  45KB (gzipped)

Optimization Potential

Original:     250KB (100%)
Minified:     180KB (72%)  - Remove whitespace, comments
Gzipped:      45KB  (18%)  - Compression
Unused removed: 30KB (12%)  - Remove unused CSS
Optimized:    30KB  (12%)  - Final target

Potential savings: 88%

Bundle Composition

Analyze what's in your bundle:

Vendor CSS (Bootstrap, etc.):  120KB (48%)
Component styles:               80KB (32%)
Utility classes:                30KB (12%)
Global styles:                  20KB (8%)

Recommendations:
1. Remove unused Bootstrap components
2. Use PurgeCSS for utilities
3. Split vendor from custom CSS

Read the full file on GitHub · 597 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 · 597 lines · 39 tokens per session scan A 33634e7eddbb

Subscribe to this mod's changes

performance-analyzer is a skill published in the GitHub repository andronics/claude-plugin-css-pro (2 stars, last pushed 10mo ago), licensed MIT. It adds 39 tokens to every session and 3,512 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 2026-08-31.

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