performance-review

A source-code review for performance costs and fragile page-loading behaviour in a buildless web project.

In plain words
What is it for?
Use it to review diffs that change scripts, page headers, images, fonts, dependencies, or page-load hooks before opening a pull request.
Why use it?
It helps identify extra bytes, network requests, or work happening too early without relying on performance measurements.

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/aemsites/author-kit/performance-review
Any agent
npx skills add aemsites/author-kit --skill performance-review
Clone the repo
git clone --depth 1 https://github.com/aemsites/author-kit

Made for: Claude Code, Codex.

Per session 66 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,331 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. 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 $0.00066 $0.02331
Opus 5 $0.00033 $0.01166
Sonnet 5 $0.00013 $0.00466
Haiku 4.5 $0.00007 $0.00233

Measured 2d ago against content hash 54b2110c0273, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

performance-review scanned grade A with 1 finding 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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

const data = fetch(url).then((r) => r.json()); // started, not awaited
.agents/skills/performance-review/SKILL.md · 188 lines

How it starts

The opening of the file, as written. The whole thing — 188 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Performance review

This project is buildless and every line ships. Regressions here are not slow functions — they are bytes and requests added before first paint, and work hoisted ahead of the lifecycle stage that should own it.

This skill analyses; it does not measure. Lighthouse against a proxied dev server produces numbers that are not the published numbers, and every check below is decidable from source.

Report findings. Do not fix them unless asked.

The lifecycle — what already happens, in order

# Where What runs Network
1 scripts.js top level setConfig, then top-level await loadPage() no
2 loadAreadecorateSession / decorateDoc (document only) header mode, template metadata, stored colour scheme, hash → localStorage no
3 decoratePictures adds the 3000px source to picture:has([loading]) no
4 config.decorateArea hook project-specific; today eager-loads the first image no
5 decorateSections .section wrapping, child regrouping, decorateLinks no
6 section loop, per section loadIcons, then link blocks, then div blocks, then section-metadata yes — dynamic import per block, parallel within a phase, sections awaited in order
7 after section 0 postlcp.js (loads the header block), deps/rum.js deferred
8 after all sections lazy.js → lazyhash, favicon, footer, author tools in non-prod deferred, post-paint

Steps 1–5 are synchronous and block the first section. Anything added there delays every paint on every page.

Parallelise with purpose

Awaited and unawaited async are both deliberate here. The pattern is consistent once you see it:

  • The LCP image and the first section's blocks race — same paint, so concurrency costs nothing and finishing sooner helps.
  • Blocks within a section run concurrently — all of them are needed for that section to render.
  • Sections are awaited one at a time — section 3's blocks racing section 0's would saturate bandwidth and delay LCP for content nobody can see yet.

Read the full file on GitHub · 188 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 · 188 lines · 66 tokens per session scan A 54b2110c0273

Subscribe to this mod's changes

performance-review is a skill published in the GitHub repository aemsites/author-kit (12 stars, last pushed 20d ago), licensed Apache-2.0. It adds 66 tokens to every session and 2,331 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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