HTML Coder Skill
Expert skill for professional HTML development with focus on semantic markup, accessibility, HTML5 features, and standards-compliant web content.
When to Use This Skill
- Creating HTML documents with semantic structure
- Building accessible forms with HTML5 validation
- Implementing responsive markup and multimedia
- Using HTML5 APIs (Canvas, SVG, Storage, Geolocation)
- Troubleshooting validation or accessibility issues
Core Capabilities
- Semantic HTML: Document structure, content sections, accessibility-first markup
- Forms: All input types, validation attributes, fieldsets, labels
- Media: Responsive images, audio/video, Canvas, SVG
- HTML5 APIs: Web Storage, Geolocation, Drag & Drop, Web Workers
- Accessibility: ARIA, screen reader support, WCAG compliance
Essential References
Core documentation for HTML experts:
references/add-css-style.md- Add CSS vialinktag, inline, or embedded in htmlreferences/add-javascript.md- Add JavaScript viascript src="link.js"tag, inlinescript, or embedded in htmlreferences/attributes.md- HTML attribute essentialsreferences/essentials.md- Semantic markup, validation, responsive techniquesreferences/global-attributes.md- Complete global attribute informationreferences/glossary.md- Complete HTML element and attribute referencereferences/standards.md- HTML5 specifications and standards
Best Practices
Semantic HTML - Use elements that convey meaning: <article>, <nav>, <header>, <section>, <footer>, not div soup.
Accessibility First - Proper heading hierarchy, alt text, labels with inputs, keyboard navigation, ARIA when needed.
HTML5 Validation - Leverage built-in validation (required, pattern, type="email") before JavaScript.
Responsive Images - Use <picture>, srcset, and loading="lazy" for performance.
Performance - Minimize DOM depth, optimize images, defer non-critical scripts, use semantic elements.
Quick Patterns
Semantic Page Structure
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Page Title</title>
</head>
<body>
<header><nav><!-- Navigation --></nav></header>
<main><article><!-- Content --></article></main>
<aside><!-- Sidebar --></aside>
<footer><!-- Footer --></footer>
</body>
</html>
Accessible Form
<form method="post" action="/submit">
<fieldset>
<legend>Contact</legend>
<label for="email">Email:</label>
<input type="email" id="email" name="email" required
pattern="[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,}$">
<button type="submit">Send</button>
</fieldset>
</form>
Responsive Image
<picture>
<source media="(min-width: 1200px)" srcset="large.webp">
<source media="(min-width: 768px)" srcset="medium.webp">
<img src="small.jpg" alt="Description" loading="lazy">
</picture>
Troubleshooting
- Validation: W3C Validator (validator.w3.org), check unclosed tags, verify nesting
- Accessibility: Lighthouse audit, screen reader testing, keyboard nav, color contrast
- Compatibility: Can I Use (caniuse.com), feature detection, provide fallbacks
Key Standards
- WHATWG HTML Living Standard: https://html.spec.whatwg.org/
- WCAG Accessibility: https://www.w3.org/WAI/WCAG21/quickref/
- MDN Web Docs: https://developer.mozilla.org/en-US/docs/Web/HTML