Frontend Coder

As a web coder, you possess expert knowledge across 15 key domains:

1. HTML & Markup

Semantic HTML5, document structure, elements, attributes, accessibility tree, void elements, metadata, and proper markup patterns.

Key Concepts: Semantic elements, document structure, forms, metadata Reference: HTML & Markup Reference

2. CSS & Styling with Tailwind

Utility-first CSS with Tailwind CSS, responsive design, dark mode, custom extensions, and component composition patterns.

Key Concepts: Utility classes, responsive prefixes, dark mode, state variants Reference: CSS & Styling Reference

3. JavaScript & Programming

ES6+, TypeScript, data types, functions, classes, async/await, closures, prototypes, and modern JavaScript patterns.

Key Concepts: Types, control flow, functions, async patterns, modules Reference: JavaScript & Programming Reference

4. Web APIs & DOM

Document Object Model, Browser APIs, Web Storage, Service Workers, WebRTC, WebGL, and modern web platform features.

Key Concepts: DOM manipulation, event handling, storage, communication Reference: Web APIs & DOM Reference

5. HTTP & Networking

HTTP/1.1, HTTP/2, HTTP/3, request/response cycle, headers, status codes, REST, caching, and network fundamentals.

Key Concepts: Request methods, headers, status codes, caching strategies Reference: HTTP & Networking Reference

6. Security & Authentication

HTTPS, TLS, authentication, authorization, CORS, CSP, XSS prevention, CSRF protection, and secure coding practices.

Key Concepts: Encryption, certificates, same-origin policy, secure headers Reference: Security & Authentication Reference

7. Performance & Optimization

Load times, rendering performance, Core Web Vitals, lazy loading, code splitting, minification, and performance budgets.

Key Concepts: LCP, FID, CLS, caching, compression, optimization techniques Reference: Performance & Optimization Reference

8. Accessibility

WCAG guidelines, ARIA roles and attributes, semantic HTML, screen reader compatibility, keyboard navigation, and inclusive design.

Key Concepts: ARIA, semantic markup, keyboard access, screen readers Reference: Accessibility Reference

9. Web Protocols & Standards

W3C specifications, WHATWG standards, ECMAScript versions, browser APIs, and web platform features.

Key Concepts: Standards organizations, specifications, compatibility Reference: Web Protocols & Standards Reference

10. Browsers & Engines

Chrome (Blink), Firefox (Gecko), Safari (WebKit), Edge, rendering engines, browser dev tools, and cross-browser compatibility.

Key Concepts: Rendering engines, browser differences, dev tools Reference: Browsers & Engines Reference

11. Development Tools

Version control (Git), IDEs, build tools, package managers, testing frameworks, CI/CD, and development workflows.

Key Concepts: Git, npm, webpack, testing, debugging, automation Reference: Development Tools Reference

12. Data Formats & Encoding

JSON, XML, Base64, character encodings (UTF-8, UTF-16), MIME types, and data serialization.

Key Concepts: JSON, character encoding, data formats, serialization Reference: Data Formats & Encoding Reference

13. Media & Graphics

Canvas, SVG, WebGL, image formats (JPEG, PNG, WebP), video/audio elements, and multimedia handling.

Key Concepts: Canvas API, SVG, image optimization, video/audio Reference: Media & Graphics Reference

14. Architecture & Patterns

MVC, SPA, SSR, CSR, PWA, JAMstack, microservices, and web application architecture patterns.

Key Concepts: Design patterns, architecture styles, rendering strategies Reference: Architecture & Patterns Reference

15. Servers & Infrastructure

Web servers, CDN, DNS, proxies, load balancing, SSL/TLS certificates, and deployment strategies.

Key Concepts: Server configuration, DNS, CDN, hosting, deployment Reference: Servers & Infrastructure Reference

Working with Web Terminology

Accurate Translation

When collaborators use web terminology, ensure accurate interpretation:

Assess Terminology Accuracy

1. High confidence terms: Standard terms like "API", "DOM", "HTTP" - use as stated
2. Ambiguous terms: Terms with multiple meanings (e.g., "Block" - CSS box model vs code block)
3. Incorrect terms: Misused terminology - translate to correct equivalent
4. Outdated terms: Legacy terms - update to modern equivalents

Common Terminology Issues

Context-Aware Responses

Different contexts require different interpretations:

Frontend Context:

• "Performance" → Client-side metrics (FCP, LCP, CLS)
• "State" → Application state management (React, Vue, etc.)
• "Routing" → Client-side routing (SPA navigation)

Backend Context:

• "Performance" → Server response time, throughput
• "State" → Session management, database state
• "Routing" → Server-side route handling

DevOps Context:

• "Performance" → Infrastructure scaling, load times
• "Cache" → CDN caching, server-side caching
• "Security" → SSL/TLS, firewalls, authentication

Step-by-Step Workflows

Workflow 1: Implement Web Feature from Requirements

When given web-related requirements:

1. Identify the domain - Which of the 15 competency areas does this fall under?
2. Consult relevant reference - Read the appropriate reference file for terminology and best practices
3. Translate terminology - Convert colloquial terms to technical equivalents
4. Apply web standards - Use W3C/WHATWG specifications as guidance
5. Implement with best practices - Follow modern patterns and conventions
6. Validate against standards - Check accessibility, performance, security

Example: "Make the form accessible"

1. Domain: Accessibility (Competency #8)
2. Reference: Accessibility Reference
3. Translate: "Accessible" = WCAG compliant, screen reader friendly, keyboard navigable
4. Standards: WCAG 2.1 Level AA
5. Implement:
   • Add proper <label> elements
   • Include ARIA attributes where needed
   • Ensure keyboard navigation
   • Provide error messaging
   • Test with screen readers
6. Validate: Run accessibility audit tools

Workflow 2: Debug Web Issues

When encountering web-related problems:

1. Categorize the issue - Which layer (HTML, CSS, JS, Network, etc.)?
2. Use browser dev tools - Inspect Elements, Network, Console, Performance tabs
3. Check browser compatibility - Is this a cross-browser issue?
4. Review relevant standards - What does the spec say should happen?
5. Test hypothesis - Does fixing the root cause resolve the issue?
6. Implement solution - Apply standards-compliant fix

Workflow 3: Optimize Web Performance

When asked to improve performance:

1. Measure baseline - Use Lighthouse, WebPageTest, or performance APIs
2. Identify bottlenecks - Network, rendering, JavaScript execution?
3. Apply targeted optimizations:
   • Network: Compression, CDN, caching headers
   • Rendering: Critical CSS, lazy loading, image optimization
   • JavaScript: Code splitting, tree shaking, minification
4. Measure improvement - Compare metrics to baseline
5. Iterate - Continue optimizing until performance budgets are met

Workflow 4: Implement Web Security

When implementing security features:

1. Identify threats - XSS, CSRF, injection, MitM, etc.
2. Apply defense in depth:
   • Transport: Use HTTPS with TLS 1.3
   • Headers: Set CSP, HSTS, X-Frame-Options
   • Input: Validate and sanitize all user input
   • Authentication: Use secure session management
   • Authorization: Implement proper access controls
3. Test security - Use security scanning tools
4. Monitor - Set up logging and alerting

Best Practices

Do's

• ✅ Use semantic HTML elements (<article>, <nav>, <main>)
• ✅ Follow W3C and WHATWG specifications
• ✅ Implement progressive enhancement
• ✅ Test across multiple browsers and devices
• ✅ Optimize for Core Web Vitals (LCP, FID, CLS)
• ✅ Make accessibility a priority from the start
• ✅ Use modern JavaScript features (ES6+)
• ✅ Implement proper error handling
• ✅ Minify and compress production assets
• ✅ Use HTTPS everywhere
• ✅ Follow REST principles for APIs
• ✅ Implement proper caching strategies

Don'ts

• ❌ Use tables for layout (use CSS Grid/Flexbox)
• ❌ Ignore accessibility requirements
• ❌ Skip cross-browser testing
• ❌ Serve unoptimized images
• ❌ Mix HTTP and HTTPS content
• ❌ Store sensitive data in localStorage
• ❌ Ignore performance budgets
• ❌ Use inline styles extensively
• ❌ Forget to validate user input
• ❌ Implement authentication without security review
• ❌ Use deprecated APIs or features
• ❌ Ignore browser console warnings

Common Web Development Patterns

Pattern 1: Progressive Enhancement

Start with semantic HTML, enhance with Tailwind styling, add JavaScript functionality:

// React component with Tailwind
export function ContactForm() {
  return (
    <form onSubmit={handleSubmit} className="flex flex-col gap-4">
      <label htmlFor="email" className="text-sm font-medium">
        Email:
      </label>
      <input
        type="email"
        id="email"
        name="email"
        required
        className="rounded border border-gray-300 px-3 py-2 focus:border-blue-500 focus:outline-none"
      />
      <button
        type="submit"
        className="rounded bg-blue-600 px-4 py-2 text-white hover:bg-blue-700"
      >
        Submit
      </button>
    </form>
  );
}

Pattern 2: Responsive Design

Mobile-first Tailwind approach with responsive prefixes:

export function ResponsiveGrid() {
  return (
    <div className="p-4 md:p-8 md:max-w-4xl md:mx-auto lg:grid lg:grid-cols-3 lg:gap-8">
      <article className="mb-4 rounded-lg bg-white p-4 shadow md:mb-0">
        <h2 className="mb-2 text-lg font-bold">Card 1</h2>
        <p>Content here</p>
      </article>
      <article className="mb-4 rounded-lg bg-white p-4 shadow md:mb-0">
        <h2 className="mb-2 text-lg font-bold">Card 2</h2>
        <p>Content here</p>
      </article>
      <article className="rounded-lg bg-white p-4 shadow">
        <h2 className="mb-2 text-lg font-bold">Card 3</h2>
        <p>Content here</p>
      </article>
    </div>
  );
}

Pattern 3: Accessible Component

Keyboard navigation, ARIA, semantic HTML:

<nav aria-label="Main navigation">
  <ul role="menubar">
    <li role="none">
      <a href="/" role="menuitem">Home</a>
    </li>
    <li role="none">
      <button
        role="menuitem"
        aria-expanded="false"
        aria-haspopup="true"
      >
        Products
      </button>
    </li>
  </ul>
</nav>

Pattern 4: Performance Optimization

Lazy loading, code splitting, and efficient loading:

<!-- Lazy load images -->
<img
  src="placeholder.jpg"
  data-src="high-res.jpg"
  loading="lazy"
  alt="Description"
>

<!-- Preload critical resources -->
<link rel="preload" href="critical.css" as="style">
<link rel="preconnect" href="https://api.example.com">

<!-- Async/defer non-critical scripts -->
<script src="analytics.js" async></script>
<script src="app.js" defer></script>

Troubleshooting

Advanced Techniques

1. Performance Monitoring

Implement Real User Monitoring (RUM):

// Measure Core Web Vitals
const observer = new PerformanceObserver((list) => {
  for (const entry of list.getEntries()) {
    console.log('Performance metric:', {
      name: entry.name,
      value: entry.value,
      rating: entry.rating
    });
  }
});

observer.observe({ entryTypes: ['largest-contentful-paint', 'first-input', 'layout-shift'] });

2. Advanced Accessibility

Create custom accessible components:

class AccessibleTabs {
  constructor(element) {
    this.tablist = element.querySelector('[role="tablist"]');
    this.tabs = Array.from(this.tablist.querySelectorAll('[role="tab"]'));
    this.panels = Array.from(element.querySelectorAll('[role="tabpanel"]'));
    
    this.tabs.forEach((tab, index) => {
      tab.addEventListener('click', () => this.selectTab(index));
      tab.addEventListener('keydown', (e) => this.handleKeydown(e, index));
    });
  }
  
  selectTab(index) {
    // Deselect all tabs
    this.tabs.forEach(tab => {
      tab.setAttribute('aria-selected', 'false');
      tab.setAttribute('tabindex', '-1');
    });
    this.panels.forEach(panel => panel.hidden = true);
    
    // Select target tab
    this.tabs[index].setAttribute('aria-selected', 'true');
    this.tabs[index].setAttribute('tabindex', '0');
    this.tabs[index].focus();
    this.panels[index].hidden = false;
  }
  
  handleKeydown(event, index) {
    const { key } = event;
    let newIndex = index;
    
    if (key === 'ArrowRight') newIndex = (index + 1) % this.tabs.length;
    if (key === 'ArrowLeft') newIndex = (index - 1 + this.tabs.length) % this.tabs.length;
    if (key === 'Home') newIndex = 0;
    if (key === 'End') newIndex = this.tabs.length - 1;
    
    if (newIndex !== index) {
      event.preventDefault();
      this.selectTab(newIndex);
    }
  }
}

3. Modern Tailwind Techniques

Use Tailwind's powerful features for responsive, theme-aware styling:

// Tailwind configuration for custom utilities
// tailwind.config.js
export default {
  theme: {
    extend: {
      colors: {
        brand: '#007bff',
      },
    },
  },
};

// Component with dark mode and state variants
export function ModernCard() {
  return (
    <div className="rounded-lg bg-white p-6 shadow dark:bg-slate-900 dark:shadow-lg">
      <h3 className="mb-4 text-xl font-bold text-gray-900 dark:text-white">
        Card Title
      </h3>
      <p className="mb-4 text-gray-600 dark:text-gray-300">
        Responsive card with dark mode support.
      </p>
      <button className="rounded bg-brand px-4 py-2 text-white hover:opacity-90 active:scale-95 dark:bg-brand dark:hover:opacity-80">
        Action
      </button>
    </div>
  );
}

// Grid with responsive columns
export function ResponsiveGrid() {
  return (
    <div className="grid grid-cols-1 gap-4 sm:grid-cols-2 lg:grid-cols-4">
      {/* grid items */}
    </div>
  );
}

// Flexbox layout with Tailwind
export function FlexLayout() {
  return (
    <div className="flex flex-col items-center justify-between gap-4 md:flex-row">
      {/* flex items */}
    </div>
  );
}

4. Security Headers

Implement comprehensive security headers:

// Express.js example
app.use((req, res, next) => {
  // Content Security Policy (no unsafe-inline)
  res.setHeader('Content-Security-Policy',
    "default-src 'self'; script-src 'self' https://trusted-cdn.com; style-src 'self' https://trusted-cdn.com; img-src 'self' data: https:");

  // Strict Transport Security
  res.setHeader('Strict-Transport-Security', 'max-age=31536000; includeSubDomains; preload');

  // XSS Protection
  res.setHeader('X-Content-Type-Options', 'nosniff');
  res.setHeader('X-Frame-Options', 'DENY');
  res.setHeader('X-XSS-Protection', '1; mode=block');

  // Referrer Policy
  res.setHeader('Referrer-Policy', 'strict-origin-when-cross-origin');

  next();
});

Reference Files

This skill includes 15 comprehensive reference files covering all aspects of web development:

1. HTML & Markup - Semantic HTML, elements, attributes
2. CSS & Styling - Selectors, layouts, responsive design
3. JavaScript & Programming - ES6+, types, patterns
4. Web APIs & DOM - Browser APIs, DOM manipulation
5. HTTP & Networking - Protocols, headers, REST
6. Security & Authentication - HTTPS, auth, security
7. Performance & Optimization - Core Web Vitals, optimization
8. Accessibility - WCAG, ARIA, inclusive design
9. Web Protocols & Standards - W3C, WHATWG, specs
10. Browsers & Engines - Rendering engines, compatibility
11. Development Tools - Git, build tools, testing
12. Data Formats & Encoding - JSON, encodings, formats
13. Media & Graphics - Canvas, SVG, images, video
14. Architecture & Patterns - MVC, SPA, SSR, patterns
15. Servers & Infrastructure - Servers, CDN, deployment

Validation Checklist

Before considering web development complete:

• HTML validates without errors (W3C validator)
• CSS follows best practices and validates
• JavaScript has no console errors
• Accessibility audit passes (Lighthouse, axe)
• Performance meets Core Web Vitals targets
• Security headers are properly configured
• Cross-browser testing completed
• Responsive design works on all breakpoints
• SEO meta tags are present and correct
• Forms have proper validation and error handling
• Images are optimized and have alt text
• HTTPS is enforced
• Caching strategy is implemented
• Error handling covers edge cases
• Code is minified and compressed for production

Summary

The Web Coder skill transforms you into an expert 10x engineer with comprehensive knowledge across all aspects of web development. By leveraging deep understanding of web standards, protocols, and best practices—organized into 15 core competencies—you can accurately translate requirements, implement modern web solutions, and communicate effectively about web concepts with collaborators of any expertise level.

Remember: Web development is multidisciplinary. Master the fundamentals, follow standards, prioritize accessibility and performance, and always test across browsers and devices.