performance-audit

performance-audit is a skill for Claude Code, Codex from serkan-ozal/browser-devtools-claude. It costs 34 tokens per session (498 once invoked), scanned A, original, MIT.

A method for examining how quickly a web page loads and responds, using Web Vitals and network timings. Web Vitals are standard measurements of website speed and stability.

In plain words
What is it for?
Use it to check loading speed, Core Web Vitals, API and resource timing, render-blocking files, JavaScript work, and layout shifts.
Why use it?
It helps identify slow requests, delayed page content, layout movement, and scripts that make a page feel unresponsive.

Skill for Claude CodeCodex

Part of the browser-devtools-mcp plugin — 7 skills, 2 commands, 6 agents, 2 MCP servers shipped together

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/serkan-ozal/browser-devtools-claude/performance-audit
Any agent
npx skills add serkan-ozal/browser-devtools-claude --skill performance-audit
Clone the repo
git clone --depth 1 https://github.com/serkan-ozal/browser-devtools-claude

Made for: Claude Code, Codex.

Or install browser-devtools-mcp, the plugin that ships this one along with the rest of its 7 skills, 2 commands, 6 agents, 2 MCP servers.

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/serkan-ozal/browser-devtools-claude/performance-audit.svg)](https://agentmods.dev/skills/serkan-ozal/browser-devtools-claude/performance-audit)
Your own site
<a href="https://agentmods.dev/skills/serkan-ozal/browser-devtools-claude/performance-audit"><img src="https://agentmods.dev/badge/skills/serkan-ozal/browser-devtools-claude/performance-audit.svg" alt="Measured on agentmods" height="20"></a>
Per session 34 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 498 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 $0.00034 $0.00498
Opus 5 $0.00017 $0.00249
Sonnet 5 $0.00007 $0.00100
Haiku 4.5 $0.00003 $0.00050

Measured 5d ago against content hash 325386422373, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, 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 5d 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-audit/SKILL.md · 71 lines

What it actually says

Performance Audit Skill

Analyze web page performance using Web Vitals and network timing metrics.

When to Use

This skill activates when:

  • User asks about page performance or speed
  • User wants to optimize load times
  • User mentions slow page or poor user experience
  • User needs Core Web Vitals metrics
  • User asks about SEO performance factors

Capabilities

Web Vitals Analysis

  • Get Core Web Vitals (o11y_get-web-vitals)
    • LCP (Largest Contentful Paint)
    • INP (Interaction to Next Paint)
    • CLS (Cumulative Layout Shift)
    • TTFB (Time to First Byte)
    • FCP (First Contentful Paint)

Network Performance

  • Analyze request timing (o11y_get-http-requests)
  • Identify slow API calls
  • Check resource sizes
  • Find blocking resources

Visual Analysis

  • Capture page at different load stages
  • Identify layout shifts visually
  • Check above-the-fold content

JavaScript Analysis

  • Profile JavaScript execution
  • Check for long tasks
  • Identify render-blocking scripts

Performance Thresholds

Metric Good Needs Work Poor
LCP ≤2.5s 2.5-4s >4s
INP ≤200ms 200-500ms >500ms
CLS ≤0.1 0.1-0.25 >0.25
TTFB ≤800ms 800-1800ms >1800ms

Audit Workflow

  1. Baseline: Get initial Web Vitals metrics
  2. Network: Analyze slow/large requests
  3. Resources: Check for render-blocking resources
  4. JavaScript: Look for long tasks
  5. Images: Check for unoptimized images
  6. Report: Summarize with recommendations

Common Issues

  • Large unoptimized images
  • Render-blocking CSS/JS
  • Too many HTTP requests
  • Slow server response (TTFB)
  • Layout shifts from dynamic content
  • Uncompressed resources
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. 5d ago First seen · 71 lines · 34 tokens per session scan A 325386422373

Subscribe to this mod's changes

performance-audit is a skill published in the GitHub repository serkan-ozal/browser-devtools-claude (8 stars, last pushed 5mo ago), licensed MIT. It adds 34 tokens to every session and 498 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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