Best Practices
FreeEnhance your web development with modern best practices.
Free · Opens the source repo
What Best Practices does
The Best Practices skill provides a comprehensive framework for applying modern web development standards, focusing on security, compatibility, and code quality. It leverages established guidelines from Lighthouse audits, ensuring that your web applications are not only functional but also secure and efficient. This skill is essential for developers who want to adhere to industry standards and improve the overall quality of their codebase.
By utilizing this skill, you can easily implement critical security measures such as enforcing HTTPS, setting up Content Security Policies (CSP), and managing security headers. It also emphasizes the importance of keeping dependencies updated and checking for vulnerabilities, which are crucial steps in maintaining a secure application. The skill includes practical examples and commands for auditing your project, making it straightforward to integrate into your development workflow.
In addition to security, the Best Practices skill addresses browser compatibility and code quality. It provides guidelines for proper HTML structure, character encoding, viewport settings, and feature detection, ensuring that your applications perform well across different browsers and devices. The skill also highlights deprecated APIs and offers modern alternatives to improve performance and user experience.
Whether you are a seasoned developer or just starting, this skill serves as a valuable resource for enhancing your web development practices. It helps you identify areas for improvement and implement best practices that lead to more secure and maintainable code.
When to use it
Use this skill when you need to modernize code, conduct a security audit, or review code quality.
When not to use it
This skill may not be suitable for legacy systems that cannot be updated to meet modern standards.
What you can build with it
Conducting a Security Audit
Use this skill to perform a thorough security audit of your web application, ensuring all best practices are followed.
Modernizing Legacy Code
Apply the guidelines from this skill to update and secure legacy codebases, making them compliant with current standards.
Ensuring Browser Compatibility
Utilize this skill to check and enhance browser compatibility across different devices and platforms.
How to install Best Practices
View source1. Install with the skills CLI
npx skills add davila7/claude-code-templates/best-practices --agent claude-code2. Or install it manually
Download the skill folder and drop it into ~/.claude/skills/ for all projects, or .claude/skills/ to scope it to one repo. Restart Claude Code so it picks up the new skill.
Anthropic's agentic coding CLI, and the reference implementation of Agent Skills. Drop a skill folder into ~/.claude/skills and Claude Code loads it automatically whenever a task matches the skill's description. Claude Code docs
Inside SKILL.md
Written by davila7Best practices
Modern web development standards based on Lighthouse best practices audits. Covers security, browser compatibility, and code quality patterns.
Security
HTTPS everywhere
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
Content Security Policy (CSP)
<!-- 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>
Security headers
# 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=()
No vulnerable libraries
# 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));
Input sanitization
// ❌ 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);
Secure cookies
// ❌ Insecure cookie
document.cookie = "session=abc123";
// ✅ Secure cookie (server-side)
Set-Cookie: session=abc123; Secure; HttpOnly; SameSite=Strict; Path=/
Browser compatibility
Doctype declaration
<!-- ❌ Missing or invalid doctype -->
<HTML>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<!-- ✅ HTML5 doctype -->
<!DOCTYPE html>
<html lang="en">
Character encoding
<!-- ❌ 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>
Viewport meta tag
<!-- ❌ 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>
Feature detection
// ❌ 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;
}
}
Polyfills (when needed)
<!-- 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>
Deprecated APIs
Avoid these
// ❌ 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');
}
Event listener passive
// ❌ 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 });
Console & errors
No console errors
// ❌ 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.');
}
Error boundaries (React)
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>
Global error handler
// 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
Production configuration
// ❌ 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',
};
Performance best practices
Avoid blocking patterns
// ❌ 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">
Efficient event handlers
// ❌ 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 management
// ❌ 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();
Code quality
Valid HTML
<!-- ❌ 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>
Semantic HTML
<!-- ❌ 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>
Image aspect ratios
<!-- ❌ 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;">
Permissions & privacy
Request permissions properly
// ❌ 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);
}
});
Permissions policy
<!-- 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')">
Audit checklist
Security (critical)
- HTTPS enabled, no mixed content
- No vulnerable dependencies (
npm audit) - CSP headers configured
- Security headers present
- No exposed source maps
Compatibility
- Valid HTML5 doctype
- Charset declared first in head
- Viewport meta tag present
- No deprecated APIs used
- Passive event listeners for scroll/touch
Code quality
- No console errors
- Valid HTML (no duplicate IDs)
- Semantic HTML elements used
- Proper error handling
- Memory cleanup in components
UX
- No intrusive interstitials
- Permission requests in context
- Clear error messages
- Appropriate image aspect ratios
Tools
| Tool | Purpose |
|---|---|
npm audit | Dependency vulnerabilities |
| SecurityHeaders.com | Header analysis |
| W3C Validator | HTML validation |
| Lighthouse | Best practices audit |
| Observatory | Security scan |
References
Frequently asked questions about Best Practices
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