# performance-optimization

A rule set for web performance: server-side rendering, CSS, JavaScript, assets and caching. Useful when your agent writes frontend code and you want a bar to hold it to.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 848 installs · ★ 286
- Author: Mindrally
- License: Apache-2.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/Mindrally/skills/tree/HEAD/performance-optimization/SKILL.md
- Updated: 2026-10-08
- HTML: https://affpapa.org/en/nevibecode/skills/mindrally-performance-optimization

## What it does

The skill hands your agent a set of principles for reviewing and rewriting frontend work. Server-side rendering comes first, ahead of client-side JavaScript, along with smaller bundles and attention to Core Web Vitals: LCP, FID, CLS. Measurement is meant to run continuously, with baselines kept as a reference point.

Inside are sections on CSS, JavaScript, assets and caching. CSS: classes instead of IDs, specificity held at 0 1 0, nesting no deeper than three levels, variables for colors and spacing, animation through transform and opacity. JavaScript: `const` over `let`, no `var`, deferred loading for non-critical scripts, code splitting, debounce and throttle on handlers, `requestAnimationFrame` for visual updates. Images get WebP and AVIF with fallbacks, `srcset`, subset fonts and `font-display: swap`.

There are also blocks on theme and component architecture, internationalization, monitoring and database queries. Worth knowing: this is guidance, not a script that fixes anything on its own. The agent applies it only when you point it at a file or a page — otherwise the rules just sit in context.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add Mindrally/skills --skill performance-optimization -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/performance-optimization/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/performance-optimization/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add Mindrally/skills --skill performance-optimization -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/performance-optimization/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add Mindrally/skills --skill performance-optimization -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/performance-optimization/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install Mindrally/skills performance-optimization
```

2. **Manually: put the files in place**
- File: `.github/skills/performance-optimization/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add Mindrally/skills --skill performance-optimization -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/Mindrally/skills --path performance-optimization
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/performance-optimization/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add Mindrally/skills --skill performance-optimization -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/Mindrally/skills/tree/HEAD/performance-optimization/SKILL.md

## When to use it
- strip unused client-side JavaScript from a bundle
- find out why Core Web Vitals dropped
- rewrite CSS without ID selectors or deep nesting
- set up caching and versioned filenames for static assets
- speed up font and image loading

## Example prompts
- go through this page and tell me what to drop from the client-side JavaScript
- check `styles/main.css` for deep nesting and ID selectors
- which images on the homepage should move to WebP and get `srcset`

## Source text · SKILL.md · Apache-2.0

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: e779a7c4609c2942.

BEGIN THIRD-PARTY FILE e779a7c4609c2942
```text
---
name: performance-optimization
description: Performance optimization guidelines for web development including server-side rendering, CSS best practices, and JavaScript optimization
metadata:
  maintainer: Mindrally
  source: https://github.com/Mindrally/skills
---

# Performance Optimization

Apply these performance optimization principles when developing web applications, themes, and frontend interfaces.

## Core Performance Principles

- Prioritize server-side rendering as a first principle, as opposed to client-side JavaScript
- Minimize client-side JavaScript to reduce bundle size and improve Time to Interactive
- Optimize for Core Web Vitals: LCP, FID, and CLS
- Measure performance continuously and establish baselines
- Consider performance impact of every architectural decision

## Server-Side Rendering

- Render content server-side whenever possible
- Use streaming rendering for faster Time to First Byte
- Implement proper caching strategies for rendered content
- Avoid blocking resources that delay rendering
- Pre-render static content where applicable

## CSS Best Practices

### Selector Efficiency
- Avoid ID selectors for styling; use classes instead
- Maintain specificity at 0 1 0 where possible
- Avoid deep nesting of selectors (max 3 levels)
- Use BEM or similar naming conventions for clarity
- Prefer class selectors over element selectors

### CSS Organization
- Use CSS variables for colors, spacing, and repeated values
- Group related styles logically
- Remove unused CSS to reduce payload
- Consider critical CSS inlining for above-the-fold content
- Use CSS containment for complex layouts

### Layout Performance
- Avoid layout thrashing (forced synchronous layouts)
- Use transform and opacity for animations (GPU accelerated)
- Minimize paint and composite operations
- Use will-change sparingly and intentionally
- Prefer flexbox and grid over floats and positioning

## JavaScript Optimization

### Code Organization
- Use the module pattern for code organization
- Prefix private methods with appropriate indicators
- Prefer const over let; avoid var
- Avoid external dependencies when native APIs suffice
- Split code into logical, loadable chunks

### Loading Strategies
- Defer non-critical JavaScript
- Use async loading for independent scripts
- Implement code splitting for large applications
- Lazy load components and routes
- Preload critical resources

### Runtime Performance
- Debounce and throttle event handlers appropriately
```
END THIRD-PARTY FILE e779a7c4609c2942

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