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 rules/virastack/ai/performancegit clone --depth 1 https://github.com/virastack/aiWhat 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 | $0.00000 | $0.00790 |
| Opus 5 | $0.00000 | $0.00395 |
| Sonnet 5 | $0.00000 | $0.00158 |
| Haiku 4.5 | $0.00000 | $0.00079 |
Grade A, and why
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 yesterday.
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 — 68 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Performance & Accessibility (Lighthouse 95+)
Constraints
- Measurement First: Avoid premature optimization. Identify specific bottlenecks via profiling (DevTools Performance tab) before applying any fixes.
- Keep or Revert: If an optimization (
useMemo,useCallback, lazy loading) does not show a measurable improvement, REVERT IT. Neutral changes add maintenance burden. - Log Attempts: Document failed performance attempts to prevent re-applying the same ineffective optimizations.
- Performance Budgets:
- Core Web Vitals: LCP ≤ 2.5s, INP ≤ 200ms, CLS ≤ 0.1.
- API & Load: API response time < 200ms (p95). Time to Interactive (TTI) < 3.5s on 4G connections.
- Bundle Size: Keep initial feature chunks < 50kb. Lazy load heavy dependencies.
- LCP Optimization: Prioritize loading the first visible hero assets or images.
- Image & Data Standards:
- Define explicit
widthandheightto prevent CLS. - Use
<picture>withsourcetags for complex art direction or resolution switching. - Prevent N+1 query patterns; strictly use pagination or optimized includes/joins for all data-driven components.
- Define explicit
- Icon & Font Strategy: Use tree-shakable icons (e.g.,
lucide-react). Applyswapdisplay strategy for fonts. - A11y SSOT: All interactive elements MUST have
aria-label,role, or an associated<label>. Maintain WCAG AA compliance (4.5:1 contrast ratio). Color alone must never convey state — pair with text, icons, or patterns. - UI Delivery: Interaction, focus, responsive breakpoints, and state completeness are enforced in
ui-components.mdc(Delivery Checklist). This file owns budgets, assets, and CLS/LCP. - Asset Links: Reference
ui-components.mdcfor Skeleton, focus, and layout implementation rules.
Bans
- Layout Shift: Forbidden to render content without reserved dimensions (use Skeletons).
- Native Img: Forbidden to use raw unoptimized
<img>tags for hero images. - Blocking JS: Forbidden to use heavy 3rd party scripts in the main thread; defer them.
- A11y Gaps: Forbidden to use
divas a button withouttabIndexandonKeyDown. - Alt Text: Forbidden to leave
altattributes empty or generic (e.g., "image").
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.
- yesterday First seen · 68 lines · 0 tokens per session scan A eba853b400f6
performance is a cursor rule published in the GitHub repository virastack/ai (23 stars, last pushed 25d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 790 tokens. 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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