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 agentmods add skills/ssheleg/sheleg-dev/frontend-performancenpx skills add ssheleg/sheleg-dev --skill frontend-performancegit clone --depth 1 https://github.com/ssheleg/sheleg-devWrote 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/ssheleg/sheleg-dev/frontend-performance)<a href="https://agentmods.dev/skills/ssheleg/sheleg-dev/frontend-performance"><img src="https://agentmods.dev/badge/skills/ssheleg/sheleg-dev/frontend-performance.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 | $0.00202 | $0.02559 |
| Opus 5 | $0.00101 | $0.01280 |
| Sonnet 5 | $0.00040 | $0.00512 |
| Haiku 4.5 | $0.00020 | $0.00256 |
Grade A, and why
frontend-performance 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 3d 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 — 166 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Frontend Performance
Optimize frontend applications for maximum Lighthouse scores and real-user performance. This skill covers the technical performance layer -- for how it looks, see sheleg-design; for what the interface must do, see super-ux.
Audit Workflow
- Measure -- Run PageSpeed Insights or Lighthouse. Record scores and failing audits.
- Diagnose -- Map each failing audit to a specific code-level cause (see checklist below).
- Prioritize -- Fix by impact: P0 blocks rendering, P1 hurts metrics, P2 is informational.
- Implement -- Apply fixes per the reference guides.
- Validate --
next build(or framework equivalent) + re-run Lighthouse. Verify no regressions.
Core Web Vitals, and the diagnostics beside them
Three metrics are Core Web Vitals. The other three are not, and the difference is not pedantry: only the first three are what Google reports and ranks on, and only they are field-measurable. TBT is a lab metric — web.dev says it "is not part of the Core Web Vitals set because they are not field-measurable" — and it stands in for INP when you have no field data. Telling a client their Speed Index is a failing Core Web Vital is telling them about a thing Google does not measure.
| Core Web Vital | Good | Needs Work | Poor |
|---|---|---|---|
| LCP (Largest Contentful Paint) | < 2.5s | 2.5-4.0s | > 4.0s |
| INP (Interaction to Next Paint) | < 200ms | 200-500ms | > 500ms |
| CLS (Cumulative Layout Shift) | < 0.1 | 0.1-0.25 | > 0.25 |
| Lab diagnostic | Good | Needs Work | Poor | Stands in for |
|---|---|---|---|---|
| FCP (First Contentful Paint) | < 1.8s | 1.8-3.0s | > 3.0s | early LCP signal |
| TBT (Total Blocking Time) | < 200ms | 200-600ms | > 600ms | INP, in the lab |
| SI (Speed Index) | < 3.4s | 3.4-5.8s | > 5.8s | perceived load |
Thresholds and the classification verified against web.dev/articles/vitals,
2026-08-16.
Performance Checklist
Fonts (LCP, FCP)
What ships with it
3 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.
- 3d ago First seen · 166 lines · 202 tokens per session scan A f963aed70c37
frontend-performance is a skill published in the GitHub repository ssheleg/sheleg-dev (2 stars, last pushed 4d ago), licensed MIT. It adds 202 tokens to every session and 2,559 once invoked, about $0.0010 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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