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Apply modern web development best practices for security, compatibility, and code quality. Use when asked to "apply best practices", "security audit", "modernize code", "code quality review", or "check for vulnerabilities".
Audit and improve web accessibility following WCAG 2.1 guidelines. Use when asked to "improve accessibility", "a11y audit", "WCAG compliance", "screen reader support", "keyboard navigation", or "make accessible".
Build AI agents on Cloudflare Workers using the Agents SDK. Load when creating stateful agents, durable workflows, real-time WebSocket apps, scheduled tasks, MCP servers, or chat applications. Covers Agent class, state management, callable RPC, Workflows integration, and React hooks. Biases towards retrieval from Cloudflare docs over pre-trained knowledge.
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.
Builds AI agents on Cloudflare using the Agents SDK with state management, real-time WebSockets, scheduled tasks, tool integration, and chat capabilities. Generates production-ready agent code deployed to Workers. Use when: user wants to "build an agent", "AI agent", "chat agent", "stateful agent", mentions "Agents SDK", needs "real-time AI", "WebSocket AI", or asks about agent "state management", "scheduled tasks", or "tool calling". Biases towards retrieval from Cloudflare docs over pre-trained knowledge.
Builds remote MCP (Model Context Protocol) servers on Cloudflare Workers with tools, OAuth authentication, and production deployment. Generates server code, configures auth providers, and deploys to Workers. Use when: user wants to "build MCP server", "create MCP tools", "remote MCP", "deploy MCP", add "OAuth to MCP", or mentions Model Context Protocol on Cloudflare. Also triggers on "MCP authentication" or "MCP deployment". Biases towards retrieval from Cloudflare docs over pre-trained knowledge.
Comprehensive Cloudflare platform skill covering Workers, Pages, storage (KV, D1, R2), AI (Workers AI, Vectorize, Agents SDK), networking (Tunnel, Spectrum), security (WAF, DDoS), and infrastructure-as-code (Terraform, Pulumi). Use for any Cloudflare development task. Biases towards retrieval from Cloudflare docs over pre-trained knowledge.
| name | best-practices |
| description | Apply modern web development best practices for security, compatibility, and code quality. Use when asked to "apply best practices", "security audit", "modernize code", "code quality review", or "check for vulnerabilities". |
| license | MIT |
| metadata | {"author":"web-quality-skills","version":"1.0"} |
Modern web development standards based on Lighthouse best practices audits. Covers security, browser compatibility, and code quality patterns.
Enforce HTTPS:
<!-- ❌ Mixed content -->
<img src="http://example.com/image.jpg">
<script src="http://cdn.example.com/script.js"></script>
<!-- ✅ HTTPS only -->
<img src="https://example.com/image.jpg">
<script src="https://cdn.example.com/script.js"></script>
<!-- ✅ Protocol-relative (will use page's protocol) -->
<img src="//example.com/image.jpg">
HSTS Header:
Strict-Transport-Security: max-age=31536000; includeSubDomains; preload
<!-- Basic CSP via meta tag -->
<meta http-equiv="Content-Security-Policy"
content="default-src 'self';
script-src 'self' https://trusted-cdn.com;
style-src 'self' 'unsafe-inline';
img-src 'self' data: https:;
connect-src 'self' https://api.example.com;">
<!-- Better: HTTP header -->
CSP Header (recommended):
Content-Security-Policy:
default-src 'self';
script-src 'self' 'nonce-abc123' https://trusted.com;
style-src 'self' 'nonce-abc123';
img-src 'self' data: https:;
connect-src 'self' https://api.example.com;
frame-ancestors 'self';
base-uri 'self';
form-action 'self';
Using nonces for inline scripts:
<script nonce="abc123">
// This inline script is allowed
</script>
# Prevent clickjacking
X-Frame-Options: DENY
# Prevent MIME type sniffing
X-Content-Type-Options: nosniff
# Enable XSS filter (legacy browsers)
X-XSS-Protection: 1; mode=block
# Control referrer information
Referrer-Policy: strict-origin-when-cross-origin
# Permissions policy (formerly Feature-Policy)
Permissions-Policy: geolocation=(), microphone=(), camera=()
# Check for vulnerabilities
npm audit
yarn audit
# Auto-fix when possible
npm audit fix
# Check specific package
npm ls lodash
Keep dependencies updated:
// package.json
{
"scripts": {
"audit": "npm audit --audit-level=moderate",
"update": "npm update && npm audit fix"
}
}
Known vulnerable patterns to avoid:
// ❌ Prototype pollution vulnerable patterns
Object.assign(target, userInput);
_.merge(target, userInput);
// ✅ Safer alternatives
const safeData = JSON.parse(JSON.stringify(userInput));
// ❌ XSS vulnerable
element.innerHTML = userInput;
document.write(userInput);
// ✅ Safe text content
element.textContent = userInput;
// ✅ If HTML needed, sanitize
import DOMPurify from 'dompurify';
element.innerHTML = DOMPurify.sanitize(userInput);
// ❌ Insecure cookie
document.cookie = "session=abc123";
// ✅ Secure cookie (server-side)
Set-Cookie: session=abc123; Secure; HttpOnly; SameSite=Strict; Path=/
<!-- ❌ Missing or invalid doctype -->
<HTML>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<!-- ✅ HTML5 doctype -->
<!DOCTYPE html>
<html lang="en">
<!-- ❌ Missing or late charset -->
<html>
<head>
<title>Page</title>
<meta charset="UTF-8">
</head>
<!-- ✅ Charset as first element in head -->
<html>
<head>
<meta charset="UTF-8">
<title>Page</title>
</head>
<!-- ❌ Missing viewport -->
<head>
<title>Page</title>
</head>
<!-- ✅ Responsive viewport -->
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Page</title>
</head>
// ❌ Browser detection (brittle)
if (navigator.userAgent.includes('Chrome')) {
// Chrome-specific code
}
// ✅ Feature detection
if ('IntersectionObserver' in window) {
// Use IntersectionObserver
} else {
// Fallback
}
// ✅ Using @supports in CSS
@supports (display: grid) {
.container {
display: grid;
}
}
@supports not (display: grid) {
.container {
display: flex;
}
}
<!-- Load polyfills conditionally -->
<script>
if (!('fetch' in window)) {
document.write('<script src="/polyfills/fetch.js"><\/script>');
}
</script>
<!-- Or use polyfill.io -->
<script src="https://polyfill.io/v3/polyfill.min.js?features=fetch,IntersectionObserver"></script>
// ❌ document.write (blocks parsing)
document.write('<script src="..."></script>');
// ✅ Dynamic script loading
const script = document.createElement('script');
script.src = '...';
document.head.appendChild(script);
// ❌ Synchronous XHR (blocks main thread)
const xhr = new XMLHttpRequest();
xhr.open('GET', url, false); // false = synchronous
// ✅ Async fetch
const response = await fetch(url);
// ❌ Application Cache (deprecated)
<html manifest="cache.manifest">
// ✅ Service Workers
if ('serviceWorker' in navigator) {
navigator.serviceWorker.register('/sw.js');
}
// ❌ Non-passive touch/wheel (may block scrolling)
element.addEventListener('touchstart', handler);
element.addEventListener('wheel', handler);
// ✅ Passive listeners (allows smooth scrolling)
element.addEventListener('touchstart', handler, { passive: true });
element.addEventListener('wheel', handler, { passive: true });
// ✅ If you need preventDefault, be explicit
element.addEventListener('touchstart', handler, { passive: false });
// ❌ Errors in production
console.log('Debug info'); // Remove in production
throw new Error('Unhandled'); // Catch all errors
// ✅ Proper error handling
try {
riskyOperation();
} catch (error) {
// Log to error tracking service
errorTracker.captureException(error);
// Show user-friendly message
showErrorMessage('Something went wrong. Please try again.');
}
class ErrorBoundary extends React.Component {
state = { hasError: false };
static getDerivedStateFromError(error) {
return { hasError: true };
}
componentDidCatch(error, info) {
errorTracker.captureException(error, { extra: info });
}
render() {
if (this.state.hasError) {
return <FallbackUI />;
}
return this.props.children;
}
}
// Usage
<ErrorBoundary>
<App />
</ErrorBoundary>
// Catch unhandled errors
window.addEventListener('error', (event) => {
errorTracker.captureException(event.error);
});
// Catch unhandled promise rejections
window.addEventListener('unhandledrejection', (event) => {
errorTracker.captureException(event.reason);
});
// ❌ Source maps exposed in production
// webpack.config.js
module.exports = {
devtool: 'source-map', // Exposes source code
};
// ✅ Hidden source maps (uploaded to error tracker)
module.exports = {
devtool: 'hidden-source-map',
};
// ✅ Or no source maps in production
module.exports = {
devtool: process.env.NODE_ENV === 'production' ? false : 'source-map',
};
// ❌ Blocking script
<script src="heavy-library.js"></script>
// ✅ Deferred script
<script defer src="heavy-library.js"></script>
// ❌ Blocking CSS import
@import url('other-styles.css');
// ✅ Link tags (parallel loading)
<link rel="stylesheet" href="styles.css">
<link rel="stylesheet" href="other-styles.css">
// ❌ Handler on every element
items.forEach(item => {
item.addEventListener('click', handleClick);
});
// ✅ Event delegation
container.addEventListener('click', (e) => {
if (e.target.matches('.item')) {
handleClick(e);
}
});
// ❌ Memory leak (never removed)
const handler = () => { /* ... */ };
window.addEventListener('resize', handler);
// ✅ Cleanup when done
const handler = () => { /* ... */ };
window.addEventListener('resize', handler);
// Later, when component unmounts:
window.removeEventListener('resize', handler);
// ✅ Using AbortController
const controller = new AbortController();
window.addEventListener('resize', handler, { signal: controller.signal });
// Cleanup:
controller.abort();
<!-- ❌ Invalid HTML -->
<div id="header">
<div id="header"> <!-- Duplicate ID -->
<ul>
<div>Item</div> <!-- Invalid child -->
</ul>
<a href="/"><button>Click</button></a> <!-- Invalid nesting -->
<!-- ✅ Valid HTML -->
<header id="site-header">
</header>
<ul>
<li>Item</li>
</ul>
<a href="/" class="button">Click</a>
<!-- ❌ Non-semantic -->
<div class="header">
<div class="nav">
<div class="nav-item">Home</div>
</div>
</div>
<div class="main">
<div class="article">
<div class="title">Headline</div>
</div>
</div>
<!-- ✅ Semantic HTML5 -->
<header>
<nav>
<a href="/">Home</a>
</nav>
</header>
<main>
<article>
<h1>Headline</h1>
</article>
</main>
<!-- ❌ Distorted images -->
<img src="photo.jpg" width="300" height="100">
<!-- If actual ratio is 4:3, this squishes the image -->
<!-- ✅ Preserve aspect ratio -->
<img src="photo.jpg" width="300" height="225">
<!-- Actual 4:3 dimensions -->
<!-- ✅ CSS object-fit for flexibility -->
<img src="photo.jpg" style="width: 300px; height: 200px; object-fit: cover;">
// ❌ Request on page load (bad UX, often denied)
navigator.geolocation.getCurrentPosition(success, error);
// ✅ Request in context, after user action
findNearbyButton.addEventListener('click', async () => {
// Explain why you need it
if (await showPermissionExplanation()) {
navigator.geolocation.getCurrentPosition(success, error);
}
});
<!-- Restrict powerful features -->
<meta http-equiv="Permissions-Policy"
content="geolocation=(), camera=(), microphone=()">
<!-- Or allow for specific origins -->
<meta http-equiv="Permissions-Policy"
content="geolocation=(self 'https://maps.example.com')">
npm audit)| Tool | Purpose |
|---|---|
npm audit | Dependency vulnerabilities |
| SecurityHeaders.com | Header analysis |
| W3C Validator | HTML validation |
| Lighthouse | Best practices audit |
| Observatory | Security scan |