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/thedecipherist/claude-code-mastery-project-starter-kit/web-performancenpx skills add TheDecipherist/claude-code-mastery-project-starter-kit --skill web-performancegit clone --depth 1 https://github.com/TheDecipherist/claude-code-mastery-project-starter-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/thedecipherist/claude-code-mastery-project-starter-kit/web-performance)<a href="https://agentmods.dev/skills/thedecipherist/claude-code-mastery-project-starter-kit/web-performance"><img src="https://agentmods.dev/badge/skills/thedecipherist/claude-code-mastery-project-starter-kit/web-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 | $0.00114 | $0.02106 |
| Opus 5 | $0.00057 | $0.01053 |
| Sonnet 5 | $0.00023 | $0.00421 |
| Haiku 4.5 | $0.00011 | $0.00211 |
Grade A, and why
web-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 4d 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 — 104 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Web Performance: Decide It Up Front
Performance is an architecture decision made at the start, not a cleanup pass at the end. The first question for anything user-facing is: what does the user need to see and interact with first, and what can wait. Build to that split. Loading everything eagerly and optimizing later is the expensive path, and it's the one Claude defaults to.
Split first paint from later, and load each accordingly
Sort every resource into two buckets and treat them differently:
- Critical, needed for first paint (above the fold, the main content and its styles): put it in the initial HTML, inline the critical CSS (see css-structure), preload the largest image and the one critical font.
- Later (below the fold, interactions, secondary features, third-party): defer it. Lazy-load below-fold images and iframes natively with
loading="lazy", no JavaScript library or IntersectionObserver needed, the browser handles it, and on an iframe it defers heavy third-party embeds like maps and video players too. Thendeferorasyncnon-critical scripts, dynamic-import offscreen components and routes, and load analytics and third-party tags late and async.
Don't let CSS or JS block first paint
CSS is render-blocking: a single large stylesheet delays the first paint until it's downloaded and parsed. Inline the above-the-fold slice and load the rest without blocking (<link rel="preload" as="style" onload="this.rel='stylesheet'">, or a media swap). A <script> in <head> without defer blocks HTML parsing; use defer (runs after parse, in order) or async (independent scripts), or put scripts at the end of <body>. Keep the number of render-blocking requests small.
The LCP element gets priority and is never lazy-loaded
The Largest Contentful Paint is usually the hero image or headline above the fold, and it's the metric users feel as "has it loaded yet." Preload it, mark it fetchpriority="high", and serve it correctly sized and compressed. Do NOT put loading="lazy" on it, that's a common mistake that delays the very thing LCP measures. Lazy-loading is for everything below the fold, not the first thing on screen.
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.
- 4d ago First seen · 104 lines · 114 tokens per session scan A babd48da3ff4
web-performance is a skill published in the GitHub repository TheDecipherist/claude-code-mastery-project-starter-kit (337 stars, last pushed 2mo ago), licensed MIT. It adds 114 tokens to every session and 2,106 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.
Other skills, from other repositories
systematic-debugging
Use when encountering any bug, test failure, or unexpected behavior, before proposing fixes.
brainstorming
You MUST use this before any creative work - creating features, building components, adding functionality, or modifying behavior. Explores user intent, requirements and design before implementation.
auto-perf-optimize
Run agent-driven VS Code performance or memory investigations. Use when asked to launch Code OSS, automate a VS Code scenario, run the Chat memory smoke runner, capture renderer heap snapshots, take workflow screenshots, compare run summaries, or drive a repeatable scenario before heap-snapshot analysis.
chat-perf
Run chat perf benchmarks and memory leak checks against the local dev build or any published VS Code version. Use when investigating chat rendering regressions, validating perf-sensitive changes to chat UI, or checking for memory leaks in the chat response pipeline.
chat-pet-sprite-creation
Use when creating or changing VS Code chat pet sprite art, sprite sheets, state animations, eye treatments, Stable/Insiders variants, or pet transitions under src/vs/workbench/contrib/chat/browser/widget/media/chatPet.
cpu-profile-analysis
Analyze V8/Chrome CPU profiles (.cpuprofile) and DevTools trace files (Trace-.json). Use when: profiling performance, investigating slow functions, comparing code paths, finding bottlenecks, analyzing timeToRequest, understanding call trees from sampling profiler data, analyzing layout/paint/rendering, investigating…