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/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.
<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="Reviewed on agentmods" width="80" 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 5.5 | $0.00058 | $0.00945 |
| Sonnet 5.5 | $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 1mo 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.
- 1mo 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 2d ago), licensed MIT. It adds 146 tokens to every session and 2,363 once invoked, about $0.0006 per session on Opus 5.5. 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.
Other skills, from other repositories
best-practices
Apply modern web development best practices for security, compatibility, and code quality. Use when asked to "apply best practices", "security audit", "modernize code", "code quality review", or "check for vulnerabilities".
tactical-ddd
Design, refactor, analyze, and review code by applying the principles and patterns of tactical domain-driven design. Triggers on: domain modeling, aggregate design, 'entity', 'value object', 'repository', 'bounded context', 'domain event', 'domain service', code touching domain/ directories, rich domain model…
api-security-scan
Review a REST/HTTP API — from its OpenAPI spec or route code — for security gaps like missing auth, broken object-level authorization, no rate limiting, and verbose errors. Reports file:line. Pure Claude Code, no signup.
api-security
OWASP API Security Top 10 (2023) with production Next.js App Router code — access control, authentication, input validation, rate limiting, security headers, data exposure, supply chain, SSRF, and AI tools on those APIs.
gotchas
Catches silent bugs that look right in a diff, compile clean, and pass happy-path tests: 200 OK HTML stand-ins, swallowed exceptions, state written before the async point of no return, module singletons shared across requests, Web APIs that fail without throwing, fresh-clone gaps, and tests that pass for the wrong…
code-readability
Makes code readable at the point of use: no floating (magic) numbers or strings without a name or a unit-and-why note nearby, names that carry units and meaning, small functions, shallow nesting, honest comments, and no dead code. Balanced by default: 0, 1, -1, named object properties, tests, and self-evident math are…