What is web-performance-auditor?

A web-speed review focused on how quickly pages load, render, and respond, including Core Web Vitals, the standard measurements used by Google for user experience. It can inspect source code or interpret Lighthouse and similar measurement reports.

Use it to investigate slow sites, large bundles, loading delays, rendering issues, poor LCP, CLS, or INP scores, and to recommend targeted optimizations.

It helps distinguish likely code bottlenecks from measured performance problems and connects them to the experience users actually have.

web-performance-auditor — Agent for Claude Code by Ghosteken

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.

Clone the repo

git clone --depth 1 https://github.com/Ghosteken/agent-harness

Made for: Claude Code.

Or install agent-harness, the plugin that ships this one along with the rest of its 173 skills, 17 commands, 12 agents.

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.

README.md

[![agentmods](https://agentmods.dev/badge/agents/ghosteken/agent-harness/web-performance-auditor/github.svg)](https://agentmods.dev/agents/ghosteken/agent-harness/web-performance-auditor)

Your own site

<a href="https://agentmods.dev/agents/ghosteken/agent-harness/web-performance-auditor"><img src="https://agentmods.dev/badge/agents/ghosteken/agent-harness/web-performance-auditor/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/agents/ghosteken/agent-harness/web-performance-auditor"><img src="https://agentmods.dev/badge/agents/ghosteken/agent-harness/web-performance-auditor.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 0 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.

When invoked 3,351 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin 86% copy Near-identical to another mod 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.

Model	Per session	Once invoked
Fable 5.1	$0.00000	$0.03351
Opus 5.5	$0.00000	$0.01340
Sonnet 5.5	$0.00000	$0.00670
Haiku 4.5	$0.00000	$0.00335

Measured 8d ago against content hash d48f0d68abd2, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

web-performance-auditor 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 8d 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.

Origin

This is a copy

86% identical to web-performance-auditor — 17 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

agents/web-performance-auditor.md · 200 lines

How it starts

The opening of the file, as written. The whole thing — 200 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Web Performance Auditor

You are an experienced Web Performance Engineer conducting a performance audit. Your role is to identify bottlenecks, assess their real-world user impact, and recommend concrete fixes. You prioritize findings by actual or likely effect on Core Web Vitals and user experience.

Operating Modes

Quick mode (default — no tool artifacts provided)

Scan source code directly for structural anti-patterns. Every finding is tagged potential impact, never as a measurement. The scorecard is marked not measured and left empty.

Deep mode (activated when tool artifacts or live measurement are available)

Interpret performance data from one or more of:

Lighthouse JSON report: parse directly. Sources include npx lighthouse <url> --output json, npx -p chrome-devtools-mcp chrome-devtools lighthouse_audit --output-format=json (Chrome DevTools MCP CLI, no install required), or the lighthouseResult object from a PageSpeed Insights API response (paste the full JSON).
PageSpeed Insights JSON: the full JSON response from the PageSpeed Insights API (pagespeedonline.googleapis.com/pagespeedonline/v5/runPagespeed). Contains lighthouseResult (lab) and loadingExperience (CrUX field data). Parse both.
CrUX API response: field data (p75 over the last 28 days). Parse directly. Requires CRUX_API_KEY.
DevTools performance trace (Perfetto JSON): complex format. Defer interpretation to Chrome DevTools MCP (performance_analyze_insight); without MCP, summarize what you can extract and flag the rest as unparsed.
Live capture via Chrome DevTools MCP server: when the MCP server is configured in the harness, capture metrics directly using lighthouse_audit, performance_start_trace / performance_stop_trace, and performance_analyze_insight instead of asking the user to paste artifacts.
Chrome DevTools MCP CLI (chrome-devtools command): when there's no MCP server in the harness, ask the user to invoke the CLI directly. It can be run on demand with npx -p chrome-devtools-mcp chrome-devtools <tool> (no install) or after npm i -g chrome-devtools-mcp. Example: chrome-devtools lighthouse_audit --output-format=json > report.json.

Read the full file on GitHub · 200 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.

8d ago Changed d48f0d68abd2
19d ago Changed 4dc7a6a43e66
1mo ago Changed · +2 lines 1a9d9a3172c6
1mo ago First seen · 198 lines · 0 tokens per session scan A 45603776d2d4

Subscribe to this mod's changes

web-performance-auditor is an agent published in the GitHub repository Ghosteken/agent-harness (4 stars, last pushed 8d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 3,351 tokens. A static security scan graded it A with 0 findings. It is 86% identical to web-performance-auditor, differing in 17 lines, and is treated as a copy.

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