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/jgamaraalv/ts-dev-kit/core-web-vitalsnpx skills add jgamaraalv/ts-dev-kit --skill core-web-vitalsgit clone --depth 1 https://github.com/jgamaraalv/ts-dev-kitWrote 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/jgamaraalv/ts-dev-kit/core-web-vitals)<a href="https://agentmods.dev/skills/jgamaraalv/ts-dev-kit/core-web-vitals"><img src="https://agentmods.dev/badge/skills/jgamaraalv/ts-dev-kit/core-web-vitals.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 | $0.00126 | $0.01375 |
| Opus 5 | $0.00063 | $0.00687 |
| Sonnet 5 | $0.00025 | $0.00275 |
| Haiku 4.5 | $0.00013 | $0.00137 |
Grade A, and why
core-web-vitals 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 6d 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 — 126 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Core Web Vitals
The three stable Core Web Vitals, each measured at the 75th percentile of real page loads (segmented by mobile and desktop):
<quick_reference>
| Metric | Measures | Good | Needs Improvement | Poor |
|---|---|---|---|---|
| LCP — Largest Contentful Paint | Loading | ≤ 2.5 s | 2.5–4.0 s | > 4.0 s |
| INP — Interaction to Next Paint | Interactivity | ≤ 200 ms | 200–500 ms | > 500 ms |
| CLS — Cumulative Layout Shift | Visual stability | ≤ 0.1 | 0.1–0.25 | > 0.25 |
A page passes Core Web Vitals only if all three metrics meet "Good" at the 75th percentile.
Supporting metrics (non-Core but diagnostic)
- FCP (First Contentful Paint) — diagnoses render-blocking resources upstream of LCP
- TTFB (Time to First Byte) — server response time; directly affects LCP
- TBT (Total Blocking Time) — lab proxy for INP; identifies long tasks
Tools matrix
| Tool | Type | LCP | INP | CLS | Notes |
|---|---|---|---|---|---|
| Chrome User Experience Report (CrUX) | Field | ✓ | ✓ | ✓ | 28-day rolling window of real users |
| PageSpeed Insights | Field + Lab | ✓ | ✓ | ✓ | Field = CrUX data; Lab = Lighthouse |
| Search Console CWV report | Field | ✓ | ✓ | ✓ | Groups URLs by template |
| Chrome DevTools Performance panel | Field + Lab | ✓ | ✓ | ✓ | Local profiling, interaction tracing |
| Lighthouse | Lab | ✓ | TBT* | ✓ | CI integration; INP → use TBT as proxy |
*Lighthouse uses Total Blocking Time (TBT) as a lab proxy for INP. TBT correlates with INP but does not replace field measurement.
Metric lifecycle
Metrics progress through: Experimental → Pending → Stable. All three current Core Web Vitals (LCP, CLS, INP) are Stable. INP replaced FID (First Input Delay) in March 2024. Changes to stable metrics follow an annual cadence with advance notice.
</quick_reference>
Quick setup: measure all three in the field
npm install web-vitals
import { onCLS, onINP, onLCP } from 'web-vitals';
function sendToAnalytics(metric) {
const body = JSON.stringify(metric);
(navigator.sendBeacon && navigator.sendBeacon('/analytics', body)) ||
fetch('/analytics', { body, method: 'POST', keepalive: true });
}
onCLS(sendToAnalytics);
onINP(sendToAnalytics);
onLCP(sendToAnalytics);
What ships with it
5 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.
- 6d ago First seen · 126 lines · 126 tokens per session scan A 7ec2e163e5f3
core-web-vitals is a skill published in the GitHub repository jgamaraalv/ts-dev-kit (15 stars, last pushed 6mo ago), licensed MIT. It adds 126 tokens to every session and 1,375 once invoked, about $0.0006 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 2026-08-30.
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