reexamine_performance

A set of coding rules for keeping web pages responsive by rendering content gradually, loading heavy resources only when needed, and avoiding unnecessary updates.

In plain words
What is it for?
Use it when reviewing or implementing lists, collapsed sections, refresh timers, images, large HTML output, and other performance-sensitive page code.
Why use it?
It reduces slow page loads, excessive browser work, and repeated rendering when data has not changed.

Cursor rule for Cursor

Install

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.

agentmods
npx agentmods add rules/homenshum/nodebenchai/reexamine_performance
Clone the repo
git clone --depth 1 https://github.com/HomenShum/NodeBenchAI

Made for: Cursor.

Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 417 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00000 $0.00417
Opus 5 $0.00000 $0.00209
Sonnet 5 $0.00000 $0.00083
Haiku 4.5 $0.00000 $0.00042

Measured 2d ago against content hash 7db91664ea9e, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

reexamine_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 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.

.cursor/rules/reexamine_performance.mdc · 41 lines

What it actually says

Re-examine: Performance

Progressive disclosure

  • Don't render 500 items at once — show 8-12 per group with "Show more"
  • Collapsed sections: don't render hidden children, use deferred rendering on expand
  • Store raw data in window._data or data-items attribute, render on demand via insertAdjacentHTML

Smart refresh

  • Polling/interval refreshes: hash the data before re-rendering
  • simpleHash(JSON.stringify(data)) compared to _lastDataHash — skip if unchanged
  • Avoids DOM thrashing on 5s intervals when nothing changed
  • Use requestAnimationFrame for batched DOM updates

Lazy loading

  • Images below the fold: loading="lazy" attribute
  • Heavy components: dynamic import / code splitting
  • IntersectionObserver for triggering loads when elements enter viewport
  • Placeholder (skeleton or blur) until loaded

String concatenation

  • Build HTML with array push + join: const h = []; h.push('<div>'); return h.join('')
  • Avoids O(n^2) string concatenation in loops
  • Template literals are fine for small chunks; arrays for large dynamic HTML

CSS performance

  • Use CSS custom properties (:root { --gap: 1rem }) instead of repeated values
  • Avoid * selectors in complex rules
  • will-change: transform only on elements that actually animate
  • contain: content on independent card/section containers

Measurement

  • Profile before optimizing — don't guess where the bottleneck is
  • Check for layout thrashing: read → write → read → write cycles
  • getComputedStyle() calls force synchronous layout — cache results
Changes

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.

  1. 2d ago First seen · 41 lines · 417 tokens per session scan A 7db91664ea9e

Subscribe to this mod's changes

reexamine_performance is a cursor rule published in the GitHub repository HomenShum/NodeBenchAI (14 stars, last pushed 18d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 417 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.