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HTML5 Doctype Checker

Checks that web pages start with the correct HTML5 doctype declaration

Source Download skill
Repository
thedaviddias/Front-End-Checklist
Stars
74,632
Licence
MIT
Files
2 files

What it does

This skill teaches an AI agent to check whether an HTML page begins with the modern HTML5 doctype, <!DOCTYPE html>, which tells browsers to use standards rendering instead of legacy Quirks Mode. When you ask it to review a page or template, the agent looks at the very first line of the raw HTML source, flags missing, outdated, or misplaced doctypes, and suggests a fix, including checking root templates in frameworks like Next.js, Vite, or Rails.

Great for

  • Front-end developers reviewing a site or template for basic HTML hygiene
  • Teams auditing legacy pages that may still use HTML4 or XHTML doctypes
  • Beginners learning why the first line of an HTML file matters

Skip it if

  • Projects needing deep HTML validation beyond the doctype, since this skill covers only that one rule
  • Situations where the agent cannot reach the rendered page or template files, because it can then only guess from partial information

Try asking

  • “Check the doctype on my index.html and tell me if anything is wrong”
  • “Audit the root templates in this Next.js project for missing doctypes”
  • “Review this HTML file for legacy HTML4 or XHTML doctype declarations”
  • “Explain why my page might be rendering in Quirks Mode”
Step-by-step guide: how to use HTML5 Doctype CheckerInstall, first run, examples, tips and FAQs

Install in 3 steps

  1. 1

    Download the skill

    The ZIP contains the 2 original files, the MIT licence and an attribution note.

    doctype.zip
  2. 2

    Add it to your agent

    Claude Code (all projects)

    mkdir -p ~/.claude/skills && unzip doctype.zip -d ~/.claude/skills/

    Claude Code / Agent SDK (this project only)

    mkdir -p .claude/skills && unzip doctype.zip -d .claude/skills/

    Claude apps (web/desktop): Settings → Capabilities → Skills → Upload skill, and choose the ZIP.

  3. 3

    Ask for the task

    No special command needed — the agent reads the skill's description and loads it when your request matches. Try one of the prompts above.

Get better results

  • Paste the raw HTML source or point the agent to the template file so it can inspect the first line directly
  • For framework projects, ask the agent to check both the root template and the rendered output in the browser
  • Ask for a specific fix, such as the exact line to add, so the agent gives you a copy-ready change

What's inside

  • references/rule.md
  • SKILL.md

Redistributed unmodified from thedaviddias/Front-End-Checklist under the MIT licence. The assessment was drafted with AI from the skill's files on 2026-10-29. Skills can instruct your agent to run code — read SKILL.md and any scripts before installing.