Borrowing it
Nothing to install: this file belongs to plugin87/full-stack-design-skills. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/plugin87/full-stack-design-skills/main/.claude/skills/web-performance-optimization/SKILL.mdgit clone --depth 1 https://github.com/plugin87/full-stack-design-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/plugin87/full-stack-design-skills/web-performance-optimization)<a href="https://agentmods.dev/skills/plugin87/full-stack-design-skills/web-performance-optimization"><img src="https://agentmods.dev/badge/skills/plugin87/full-stack-design-skills/web-performance-optimization/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/plugin87/full-stack-design-skills/web-performance-optimization"><img src="https://agentmods.dev/badge/skills/plugin87/full-stack-design-skills/web-performance-optimization.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 | $0.00111 | $0.03887 |
| Opus 5.5 | $0.00044 | $0.01555 |
| Sonnet 5.5 | $0.00022 | $0.00777 |
| Haiku 4.5 | $0.00011 | $0.00389 |
Grade A, and why
web-performance-optimization 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 2mo 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 — 514 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Web Performance Optimization
A practical guide to measuring, diagnosing, and improving web application performance.
Performance is a user experience feature. A fast site converts better, keeps users engaged, and ranks higher in search. This skill covers the metrics that matter, tools that measure them, and concrete optimization strategies.
Core Web Vitals: The Three Metrics That Matter
Google's Core Web Vitals are the three quantitative measures of user experience. They directly impact search rankings and user satisfaction.
1. Largest Contentful Paint (LCP)
What it measures: How fast the largest visible element (text, image, video) appears on screen.
Target: < 2.5 seconds
Why it matters: Users perceive "fast" as "appears quickly." If the main content takes 4+ seconds, users bounce.
What counts as LCP:
<img>elements<image>inside<svg>- Backgrounds with
background-image - Text blocks (paragraphs, headings)
- Videos (poster frame)
- Canvas elements
What doesn't count:
- Off-screen images
- Transparent images
- Text in canvas
Example LCP Timeline:
0s — Page begins to load
0.8s — Hero image starts loading
1.2s — Hero image finishes (LCP = 1.2s) ✓ Good (< 2.5s)
2.1s — Page fully interactive
Optimization strategies:
- Preload critical images (
<link rel="preload">) - Compress images aggressively (WebP format, lazy loading for below-the-fold)
- Use a CDN for fast global delivery
- Avoid render-blocking CSS/JavaScript
- Use server-side rendering for critical content
2. First Input Delay (FID) → Interaction to Next Paint (INP)
What it measures: Delay between user input (click, tap, keystroke) and browser response.
Target: < 100ms (FID) or < 200ms (INP)
Why it matters: Slow response feels like the app is frozen. Users think something broke and abandon the interaction.
FID vs. INP:
- FID (First Input Delay): Only measures the first user interaction. Being fast once doesn't mean consistently fast.
- INP (Interaction to Next Paint): Measures all interactions throughout the page lifetime. More realistic; now recommended over FID.
What ships with it
6 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.
- 2mo ago First seen · 514 lines · 0 tokens per session scan A 66646e1beaf7
web-performance-optimization is a skill published in the GitHub repository plugin87/full-stack-design-skills (11 stars, last pushed 3mo ago), licensed MIT. It adds 111 tokens to every session and 3,887 once invoked, about $0.0004 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.
web-performance-optimization compared with skills from other repositories
| Mod | Type | Stars | Last push | Licence | Scan | Tokens | Works with |
|---|---|---|---|---|---|---|---|
| web-performance-optimizationplugin87/full-stack-design-skills | Skill | 11 | 3mo ago | MIT | A | 111 | Claude Code |
| anti-slop-designsickn33/agentic-awesome-skills | Skill | 49k | yesterday | MIT | A | 34 | Claude Code |
| chakra-ui-builderchakra-ui/chakra-ui | Skill | 41k | yesterday | MIT | A | 214 | Claude Code, Codex |
| visual-ralphYeachan-Heo/oh-my-codex | Skill | 34k | 3d ago | MIT | A | 52 | Codex |
| open-design-setupcompozy/compozy | Skill | 2.8k | yesterday | MIT | A | 67 | Claude Code, Codex |
| edit-sitemicrosoft/power-platform-skills | Skill | 1.1k | yesterday | MIT | A | 104 | Claude Code |
| frontend-visual-qadaymade/claude-code-skills | Skill | 1.5k | yesterday | MIT | A | 125 | Claude Code, Codex |