# W3c Compliant

> Use when reviewing templates, rendered HTML, or shared components related to Validate HTML against W3C standards. Validate the final browser-facing markup, not just the source framework abstraction.

- Skill: `thedaviddias/w3c-compliant` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add thedaviddias/w3c-compliant`
- Raw SKILL.md: https://api.skillmd.com/api/skills/thedaviddias/w3c-compliant/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Web & Frontend
- Author: thedaviddias (https://skillmd.com/u/thedaviddias)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/thedaviddias/w3c-compliant

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# Validate HTML against W3C standards

Invalid HTML causes unpredictable rendering across browsers, breaks accessibility tools, and makes debugging significantly harder.

## Quick Reference

- Use validator.w3.org or browser extensions for validation
- Fix errors first, then warnings (errors cause rendering issues)
- Integrate validation into CI/CD with html-validate
- Common issues: unclosed tags, invalid nesting, missing attributes

## Check

Validate HTML markup using the W3C HTML Validator to identify and fix markup errors that could cause cross-browser compatibility issues.

## Fix

Run HTML through W3C validator and fix reported errors including unclosed tags, missing attributes, and invalid nesting.

## Explain

Explain why W3C HTML validation is important for cross-browser compatibility, accessibility, and maintainable code.

## Code Review

Review templates, server-rendered HTML, and shared components that output markup related to Validate HTML against W3C standards. Flag exact elements, attributes, and routes where the rendered HTML violates the rule.

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For full implementation details, code examples, and framework-specific guidance,
see `references/rule.md`.

Rule page: https://frontendchecklist.io/en/rules/html/w3c-compliant