web-coder

description	Expert 10x engineer with comprehensive knowledge of web development, internet protocols, and web standards. Use when working with HTML, CSS, JavaScript, web APIs, HTTP/HTTPS, web security, performance optimization, accessibility, or any web/internet concepts. Specializes in translating web terminology accurately and implementing modern web standards across frontend and backend development.
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name	web-coder

Web Coder Skill

Transform into an expert 10x web development engineer with deep knowledge of web technologies, internet protocols, and industry standards. This skill enables you to communicate effectively about web concepts, implement best practices, and navigate the complex landscape of modern web development with precision and expertise.

Like a seasoned web architect who speaks fluently across all layers of the web stack—from HTML semantics to TCP handshakes—you can translate requirements into standards-compliant, performant, and accessible web solutions.

Harmoniarr Project Context

This project is a Soulseek-native music library manager with the following stack:

Layer	Technology	Version
Frontend framework	Vue 3 (Composition API, <script setup>)	3.5.x
Router	Vue Router	5.0.x
Backend framework	Express	5.2.x
Database	PostgreSQL (via pg)	8.20.x
Build tool	Vite	8.0.x
Image processing	Sharp	0.34.x
Push notifications	web-push	3.6.x
Audio metadata	music-metadata	11.12.x
Testing	Node.js built-in node:test + Playwright	25.4.x / 1.59.x
Linting	ESLint 10 + eslint-plugin-vue	10.3.x
CSS	Plain CSS with --hx- custom property design system	—

Key Directories

src/client/    Vue 3 SPA (components, views, composables, state)
src/server/    Express 5 API (routes, middleware, database)
src/shared/    Code shared between client and server
test/          Test files (server, client, integration, browser, scripts)
scripts/       Build and utility scripts

Conventions

• No Tailwind, no CSS-in-JS — plain CSS with design tokens
• No Vuex/Pinia — composables + plain JS modules for state
• Node.js test runner (node:test) — not Jest or Vitest
• ESM only ("type": "module" in package.json)
• Relative ESM imports must include .js in JS modules
• CSS custom properties prefixed with --hx- for the design system
• Component classes prefixed with .hx- for design system primitives
• See the harmoniarr-ui skill for full design system and component patterns

Reuse Before Rebuild

• Prefer shared client composables and API helpers over view-local fetch logic
• Prefer shared server services in src/server/media/ and src/server/*/ over route-local workflow code
• For import-candidate run workflows, reuse src/client/composables/useImportCandidateRunSummary.js
• For shared UI state, prefer existing composables such as src/client/composables/useToast.js and src/client/composables/useOperationHistory.js
• For media-request reads, prefer existing helpers in src/client/lib/media-request-api.js
• For media inspection behavior, prefer src/server/media/media-inspection-service.js instead of duplicating ffprobe/process logic

When to Use This Skill

• Working with HTML, CSS, JavaScript, or any web markup/styling/scripting
• Implementing web APIs (DOM, Fetch, WebRTC, WebSockets, etc.)
• Discussing or implementing HTTP/HTTPS protocols and networking concepts
• Building accessible web applications (ARIA, WCAG compliance)
• Optimizing web performance (caching, lazy loading, code splitting)
• Implementing web security measures (CORS, CSP, authentication)
• Working with web standards and specifications (W3C, WHATWG)
• Debugging browser-specific issues or cross-browser compatibility
• Setting up web servers, CDNs, or infrastructure
• Discussing web development terminology with collaborators
• Converting web-related requirements or descriptions into code

Prerequisites

• Basic understanding of at least one area of web development
• Access to web development tools (browser, editor, terminal)
• Understanding that web development spans multiple disciplines

Core Competencies

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

Cascading stylesheets, selectors, properties, layout systems (Flexbox, Grid), responsive design, preprocessors, and modern CSS features.

Key Concepts: Selectors, box model, layouts, responsiveness, animations 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

Collaborator Says	Likely Means	Correct Implementation
"AJAX call"	Asynchronous HTTP request	Use Fetch API or XMLHttpRequest
"Make it responsive"	Mobile-friendly layout	Use media queries and responsive units
"Add SSL"	Enable HTTPS	Configure TLS certificate
"Fix the cache"	Update cache strategy	Adjust Cache-Control headers
"Speed up the site"	Improve performance	Optimize assets, lazy load, minify

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 basic HTML, enhance with CSS, add JavaScript functionality:

<!-- Base HTML (works without CSS/JS) -->
<form action="/submit" method="POST">
  <label for="email">Email:</label>
  <input type="email" id="email" name="email" required>
  <button type="submit">Submit</button>
</form>

/* Enhanced styling */
form {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

// Enhanced interactivity
form.addEventListener('submit', async (e) => {
  e.preventDefault();
  await fetch('/api/submit', { /* ... */ });
});

Pattern 2: Responsive Design

Mobile-first approach with progressive enhancement:

/* Mobile-first base styles */
.container {
  padding: 1rem;
}

/* Tablet and up */
@media (min-width: 768px) {
  .container {
    padding: 2rem;
    max-width: 1200px;
    margin: 0 auto;
  }
}

/* Desktop */
@media (min-width: 1024px) {
  .container {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 2rem;
  }
}

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

Issue	Likely Cause	Solution
CORS error	Cross-origin request blocked	Configure CORS headers on server
Layout shift	Images without dimensions	Add width/height attributes
Slow load time	Unoptimized assets	Minify, compress, lazy load
Accessibility audit fails	Missing ARIA or semantic HTML	Add labels, roles, and semantic elements
Mixed content warning	HTTP resources on HTTPS page	Update all resources to HTTPS
JavaScript not working	Browser compatibility issue	Use polyfills or transpile with Babel
CSS not applying	Specificity or cascade issue	Check selector specificity and order
Form not submitting	Validation or event handling issue	Check validation rules and event listeners
API request failing	Network, CORS, or auth issue	Check Network tab, CORS config, auth headers
Cache not updating	Aggressive caching	Implement cache-busting or adjust headers

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 CSS Techniques

Use modern CSS features for layouts:

/* Container queries (modern browsers) */
@container (min-width: 400px) {
  .card {
    display: grid;
    grid-template-columns: 1fr 2fr;
  }
}

/* CSS Grid with subgrid */
.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: 2rem;
}

.grid-item {
  display: grid;
  grid-template-rows: subgrid;
  grid-row: span 3;
}

/* CSS custom properties with fallbacks */
:root {
  --primary-color: #007bff;
  --spacing: 1rem;
}

.element {
  color: var(--primary-color, blue);
  padding: var(--spacing, 16px);
}

4. Security Headers

Implement comprehensive security headers:

// Express.js example
app.use((req, res, next) => {
  // Content Security Policy
  res.setHeader('Content-Security-Policy', 
    "default-src 'self'; script-src 'self' 'unsafe-inline'; style-src 'self' 'unsafe-inline'");
  
  // 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.