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/nucliweb/webperf-snippets/webperf-loadingnpx skills add nucliweb/webperf-snippets --skill webperf-loadinggit clone --depth 1 https://github.com/nucliweb/webperf-snippetsWhat 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 | $0.00172 | $0.02663 |
| Opus 5 | $0.00086 | $0.01332 |
| Sonnet 5 | $0.00034 | $0.00533 |
| Haiku 4.5 | $0.00017 | $0.00266 |
Grade A, and why
webperf-loading 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 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.
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 — 218 lines — stays where its author put it; the contents beside it link to each section on GitHub.
WebPerf: Loading Performance
JavaScript snippets for measuring web performance in Chrome DevTools. Execute with mcp__chrome-devtools__evaluate_script, capture output with mcp__chrome-devtools__get_console_message.
Scripts
scripts/Back-Forward-Cache.js— Back Forward Cachescripts/CSS-Media-Queries-Analysis.js— CSS Media Queries Analysisscripts/Cache-Strategy-Analysis.js— Cache Strategy Analysisscripts/Client-Side-Redirect-Detection.js— Client Side Redirect Detectionscripts/Content-Visibility.js— Content Visibilityscripts/Critical-CSS-Detection.js— Critical CSS Detectionscripts/Event-Processing-Time.js— Event Processing Timescripts/FCP.js— First Contentful Paint (FCP)scripts/Find-Above-The-Fold-Lazy-Loaded-Images.js— Find Above The Fold Lazy Loaded Imagesscripts/Find-Images-With-Lazy-and-Fetchpriority.js— Find Images With Loading Lazy and Fetchpriorityscripts/Find-non-Lazy-Loaded-Images-outside-of-the-viewport.js— Find non Lazy Loaded Images outside of the viewportscripts/Find-render-blocking-resources.js— Find render-blocking resourcesscripts/First-And-Third-Party-Script-Info.js— First And Third Party Script Infoscripts/First-And-Third-Party-Script-Timings.js— First And Third Party Script Timingsscripts/Fonts-Preloaded-Loaded-and-used-above-the-fold.js— Fonts Preloaded, Loaded, and Used Above The Foldscripts/Inline-CSS-Info-and-Size.js— Inline CSS Info and Sizescripts/Inline-Script-Info-and-Size.js— Inline Script Info and Sizescripts/JS-Execution-Time-Breakdown.js— JavaScript Execution Time Breakdownscripts/Prefetch-Resource-Validation.js— Prefetch Resource Validationscripts/Priority-Hints-Audit.js— Priority Hints Auditscripts/Resource-Hints-Validation.js— Resource Hints Validationscripts/Resource-Hints.js— Resource Hintsscripts/SSR-Hydration-Data-Analysis.js— SSR Framework Hydration Data Analysisscripts/Script-Loading.js— Scripts Loadingscripts/Service-Worker-Analysis.js— Service Worker Analysisscripts/TTFB-Resources.js— Time To First Byte: Measure TTFB for all resourcesscripts/TTFB-Sub-Parts.js— Time To First Byte: Measure TTFB sub-partsscripts/TTFB.js— Time To First Byte: Measure the time to first bytescripts/Validate-Preload-Async-Defer-Scripts.js— Validate Preload Async Defer Scripts
What ships with it
31 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.
- references/schema.md 20 KB
- references/snippets.md 8.6 KB
- scripts/Back-Forward-Cache.js 4.0 KB runs code
- scripts/Cache-Strategy-Analysis.js 9.5 KB runs code
- scripts/Client-Side-Redirect-Detection.js 2.1 KB runs code
- scripts/Content-Visibility.js 3.7 KB runs code
- scripts/Critical-CSS-Detection.js 3.1 KB runs code
- scripts/CSS-Media-Queries-Analysis.js 3.6 KB runs code
- scripts/Event-Processing-Time.js 3.2 KB runs code
- scripts/FCP.js 864 B runs code
- scripts/Find-Above-The-Fold-Lazy-Loaded-Images.js 3.3 KB runs code
- scripts/Find-Images-With-Lazy-and-Fetchpriority.js 1.5 KB runs code
- scripts/Find-non-Lazy-Loaded-Images-outside-of-the-viewport.js 3.5 KB runs code
- scripts/Find-render-blocking-resources.js 1.5 KB runs code
- scripts/First-And-Third-Party-Script-Info.js 2.1 KB runs code
- scripts/First-And-Third-Party-Script-Timings.js 3.2 KB runs code
- scripts/Fonts-Preloaded-Loaded-and-used-above-the-fold.js 2.9 KB runs code
- scripts/Inline-CSS-Info-and-Size.js 2.7 KB runs code
- scripts/Inline-Script-Info-and-Size.js 3.7 KB runs code
- scripts/JS-Execution-Time-Breakdown.js 3.3 KB runs code
- scripts/Prefetch-Resource-Validation.js 4.7 KB runs code
- scripts/Priority-Hints-Audit.js 3.6 KB runs code
- scripts/Resource-Hints-Validation.js 3.3 KB runs code
- scripts/Resource-Hints.js 4.4 KB runs code
- scripts/Script-Loading.js 3.6 KB runs code
- scripts/Service-Worker-Analysis.js 1001 B runs code
- scripts/SSR-Hydration-Data-Analysis.js 3.6 KB runs code
- scripts/TTFB-Resources.js 1.4 KB runs code
- scripts/TTFB-Sub-Parts.js 1.7 KB runs code
- scripts/TTFB.js 533 B runs code
- scripts/Validate-Preload-Async-Defer-Scripts.js 3.9 KB runs code
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.
- 2d ago First seen · 218 lines · 172 tokens per session scan A 657830449fb5
webperf-loading is a skill published in the GitHub repository nucliweb/webperf-snippets (1,445 stars, last pushed 1mo ago), licensed MIT. It adds 172 tokens to every session and 2,663 once invoked, about $0.0009 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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