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.
npx skills add Kin9Zeus/senior-engineer-skills --skill performance-engineeringgit clone --depth 1 https://github.com/Kin9Zeus/senior-engineer-skillsWrote 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.
[](https://agentmods.dev/skills/kin9zeus/senior-engineer-skills/performance-engineering)<a href="https://agentmods.dev/skills/kin9zeus/senior-engineer-skills/performance-engineering"><img src="https://agentmods.dev/badge/skills/kin9zeus/senior-engineer-skills/performance-engineering.svg" alt="Measured on agentmods" height="20"></a>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 | $0.00146 | $0.02363 |
| Opus 5 | $0.00073 | $0.01182 |
| Sonnet 5 | $0.00029 | $0.00473 |
| Haiku 4.5 | $0.00015 | $0.00236 |
Grade A, and why
performance-engineering 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.
How it starts
The opening of the file, as written. The whole thing — 233 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Performance Engineering
Three rules, in order:
- Measure first. Optimising the wrong thing is worse than doing nothing — it costs time and adds complexity for no gain.
- Fix the biggest thing. Performance work follows a power law; one bottleneck usually dominates.
- Set a budget and enforce it in CI. Performance regresses by accretion, one small addition at a time, and is only ever recovered by deliberate effort.
Never report "this will be slow" without a measurement. Never report a measurement without saying what it was measured on.
Frontend: the numbers that matter
Core Web Vitals, measured at the 75th percentile of real users — not from your laptop on office wifi.
| Metric | Good | Needs work | Poor | What it measures |
|---|---|---|---|---|
| LCP | ≤ 2.5s | ≤ 4.0s | > 4.0s | When the main content appears |
| INP | ≤ 200ms | ≤ 500ms | > 500ms | Responsiveness to interaction |
| CLS | ≤ 0.1 | ≤ 0.25 | > 0.25 | Visual stability |
Supporting: TTFB (≤ 800ms), total JavaScript, and total page weight.
Lab vs field. Lighthouse is a lab tool: reproducible, useful for catching regressions, and not what your users experience. Field data (Chrome UX Report, or your own real-user monitoring) is the truth. Use lab to iterate, field to decide.
LCP — usually the highest-leverage fix
LCP is almost always an image or a heading blocked by something.
- Find the element. Chrome DevTools Performance panel marks it; PageSpeed Insights names it.
- Attack the chain in this order:
- TTFB — slow server, no CDN, no caching, a slow database query in the render path.
- Render-blocking resources — synchronous CSS and JS in
<head>. Inline critical CSS, defer the rest. - Resource load time — the image itself: format, size, compression.
- Element render delay — waiting on JavaScript, or on a font.
- Preload the LCP image (
<link rel="preload" fetchpriority="high">), and never lazy-load it. Lazy-loading the hero image is one of the most common self-inflicted LCP problems.
What ships with it
2 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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 First seen · 233 lines · 146 tokens per session scan A 9baa831788be
performance-engineering is a skill published in the GitHub repository Kin9Zeus/senior-engineer-skills (3 stars, last pushed 14d ago), licensed MIT. It adds 146 tokens to every session and 2,363 once invoked, about $0.0007 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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