A set of guidelines for improving software performance, with advice for measuring problems before changing code. It covers databases, React interfaces, network requests, and build output.

Use it to investigate slow queries, excessive React updates, large network responses, unbatched requests, and oversized application builds.

It helps avoid guessing at optimizations and focuses work on the part of the system that is actually slow, while keeping correctness as a priority.

performance — Cursor rule for Cursor by jy315189/everything-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.

Clone the repo

git clone --depth 1 https://github.com/jy315189/everything-cursor

Made for: Cursor.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/rules/jy315189/everything-cursor/performance/github.svg)](https://agentmods.dev/rules/jy315189/everything-cursor/performance)

Your own site

<a href="https://agentmods.dev/rules/jy315189/everything-cursor/performance"><img src="https://agentmods.dev/badge/rules/jy315189/everything-cursor/performance/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.

Your own site · 80×15

<a href="https://agentmods.dev/rules/jy315189/everything-cursor/performance"><img src="https://agentmods.dev/badge/rules/jy315189/everything-cursor/performance.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 0 Nothing until a file matches its globs; then the whole rule loads.

When invoked 390 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

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.

Model	Per session	Once invoked
Fable 5.1	$0.00000	$0.00390
Opus 5.5	$0.00000	$0.00156
Sonnet 5.5	$0.00000	$0.00078
Haiku 4.5	$0.00000	$0.00039

Measured 1mo ago against content hash a54714e8cee4, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

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 1mo 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/performance.mdc · 41 lines

What it actually says

Performance Rules

First Principles

Measure before optimizing — profile, don't guess
Correctness before performance — fast + wrong = useless
Optimize the bottleneck — 80% of time is in 20% of code

Database

No N+1 queries — use include, join, or dataloader
Index every WHERE, JOIN, ORDER BY column — check query plans
Paginate large result sets — cursor-based for >1000 rows

React

useMemo / useCallback — ONLY when measured performance issue exists
React.memo — ONLY for components that re-render often with same props
Virtualize lists > 100 items — use @tanstack/react-virtual
Lazy load heavy components — React.lazy() + Suspense
Avoid re-render cascades — don't put frequently-changing state in Context

Network

Batch API calls — Promise.all for independent requests
Cache server data — TanStack Query / SWR with appropriate staleTime
Debounce user input — search, resize, scroll handlers (300ms default)
Compress responses — gzip/brotli on server

Build

Code split by route — dynamic import() for route components
Tree-shake — use ESM, avoid barrel re-exports of large modules
Optimize images — WebP/AVIF format, responsive sizes, lazy loading

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.

1mo ago First seen · 41 lines · 0 tokens per session scan A a54714e8cee4

Subscribe to this mod's changes

performance is a cursor rule published in the GitHub repository jy315189/everything-cursor (2 stars, last pushed 8mo ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 390 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 2026-08-31.

Debugging

error-handling-and-validation

A code-quality guide for handling errors, invalid inputs, edge cases, preconditions, logging, and user-friendly error messages.

holtwood/awesome-cursorrules-zh · 185 tokens

css-render-blocking-diagnosis

Cursor rule "css-render-blocking-diagnosis" from adobecom/da-express-milo, covering css render-blocking diagnosis & resolution, critical learning from 98 pagespeed achievement, primary diagnostic protocol, step 1: css blocking symptom recognition and step 2: css loading sequence audit.

adobecom/da-express-milo · 1,102 tokens

performance