# HTML Coder

> Expert HTML development skill for building web pages, forms, and interactive content. Use when creating HTML documents, structuring web content, implementing semantic markup, adding forms and media, working with HTML5 APIs, or needing HTML templates, best practices, and accessibility guidance. Supports modern HTML5 standards and responsive design patterns.

- Skill: `gabrielmoreira/html-coder` (Agent Skill)
- Install (CLI): `npx skillmds@latest add gabrielmoreira/html-coder`
- Raw SKILL.md: https://api.skillmd.com/api/skills/gabrielmoreira/html-coder/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Web & Frontend
- Author: gabrielmoreira (https://skillmd.com/u/gabrielmoreira)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/gabrielmoreira/html-coder

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# 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

## OpenSquilla Webpage Delivery

For a new runnable webpage when workspace file-authoring tools are available:

1. Create a filesystem-safe, dedicated project subdirectory such as
   `webpage-<topic-slug>/`; never place a generated site directly in the
   workspace root.
2. Keep `index.html`, local CSS/JavaScript, and every local asset inside that
   project root, using browser-relative references.
3. Validate the finished project, then call `publish_artifact` exactly once
   with the entry file and the complete dedicated root:

```json
{
  "path": "webpage-<topic-slug>/index.html",
  "mime": "text/html",
  "bundle": "directory",
  "bundle_root": "webpage-<topic-slug>"
}
```

Do not bundle the entire workspace. When a caller explicitly requests
source-only output, forbids tool calls, or supplies its own deterministic
writer—as AwesomeWebpageMetaSkill does—follow that narrower caller contract
instead. When file authoring or `publish_artifact` is unavailable, return only
the requested guidance or source and do not claim that a runnable project was
published.

## 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`](references/add-css-style.md) - Add CSS via `link` tag, inline, or embedded in html
- [`references/add-javascript.md`](references/add-javascript.md) - Add JavaScript via `script src="link.js"` tag, inline `script`, or embedded in html
- [`references/attributes.md`](references/attributes.md) - HTML attribute essentials
- [`references/essentials.md`](references/essentials.md) - Semantic markup, validation, responsive techniques
- [`references/global-attributes.md`](references/global-attributes.md) - Complete global attribute information
- [`references/glossary.md`](references/glossary.md) - Complete HTML element and attribute reference
- [`references/standards.md`](references/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
```html
<!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
```html
<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
```html
<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

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