Web Artifacts Builder
anthropics/skills
Builds multi-component claude.ai HTML artifacts as a small React, TypeScript and Tailwind project, then bundles it into one shareable HTML file.
A skill your agent uses when applies to XHTML documents and polyglot HTML documents that must parse correctly as both HTML5 and XML.
Install HTML XML Lang Mismatch
$ npx skills add thedaviddias/Front-End-Checklist --skill html-xml-lang-mismatch -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install thedaviddias/Front-End-Checklist html-xml-lang-mismatch --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/thedaviddias/Front-End-Checklist.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/html-xml-lang-mismatch .claude/skills/html-xml-lang-mismatch && rm -rf skills-srcUse ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.
Claude Code skills documentation · loads skills from .claude/skills/
Install the "html-xml-lang-mismatch" agent skill from https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/html-xml-lang-mismatch into .claude/skills/html-xml-lang-mismatch/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "html-xml-lang-mismatch", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/html-xml-lang-mismatchType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add thedaviddias/Front-End-Checklist --skill html-xml-lang-mismatch -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install thedaviddias/Front-End-Checklist html-xml-lang-mismatch --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/thedaviddias/Front-End-Checklist.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/html-xml-lang-mismatch .agents/skills/html-xml-lang-mismatch && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "html-xml-lang-mismatch" agent skill from https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/html-xml-lang-mismatch into .agents/skills/html-xml-lang-mismatch/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "html-xml-lang-mismatch", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add thedaviddias/Front-End-Checklist --skill html-xml-lang-mismatch -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install thedaviddias/Front-End-Checklist html-xml-lang-mismatch --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/thedaviddias/Front-End-Checklist.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/html-xml-lang-mismatch .cursor/skills/html-xml-lang-mismatch && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "html-xml-lang-mismatch" agent skill from https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/html-xml-lang-mismatch into .cursor/skills/html-xml-lang-mismatch/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "html-xml-lang-mismatch", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/thedaviddias/Front-End-Checklist.git --path skills/html-xml-lang-mismatch--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add thedaviddias/Front-End-Checklist --skill html-xml-lang-mismatch -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install thedaviddias/Front-End-Checklist html-xml-lang-mismatch --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/thedaviddias/Front-End-Checklist.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/html-xml-lang-mismatch .gemini/skills/html-xml-lang-mismatch && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "html-xml-lang-mismatch" agent skill from https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/html-xml-lang-mismatch into .gemini/skills/html-xml-lang-mismatch/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "html-xml-lang-mismatch", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install thedaviddias/Front-End-Checklist html-xml-lang-mismatchInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add thedaviddias/Front-End-Checklist --skill html-xml-lang-mismatch -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/thedaviddias/Front-End-Checklist.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/html-xml-lang-mismatch .github/skills/html-xml-lang-mismatch && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "html-xml-lang-mismatch" agent skill from https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/html-xml-lang-mismatch into .github/skills/html-xml-lang-mismatch/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "html-xml-lang-mismatch", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add thedaviddias/Front-End-Checklist --skill html-xml-lang-mismatch -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install thedaviddias/Front-End-Checklist html-xml-lang-mismatch --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/thedaviddias/Front-End-Checklist.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/html-xml-lang-mismatch .opencode/skills/html-xml-lang-mismatch && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "html-xml-lang-mismatch" agent skill from https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/html-xml-lang-mismatch into .opencode/skills/html-xml-lang-mismatch/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "html-xml-lang-mismatch", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
html-xml-lang-mismatch- GitHub stars
- 74k
- Token cost
- ~799 tokens
- SKILL.md length
- 391 words
- Files
- 2 (incl. references)
- Skills in repo
- 390
- Repo updated
- First seen
- Licence
- MIT
At a glance
A skill your agent uses when applies to XHTML documents and polyglot HTML documents that must parse correctly as both HTML5 and XML.
- Applies to XHTML documents and polyglot HTML documents that must parse correctly as both HTML5 and XML
- SKILL.md covers Quick Reference, Check, Fix and Explain, plus 1 more section
- Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
What it does
HTML XML Lang Mismatch is an agent skill from thedaviddias/Front-End-Checklist. Use when applies to XHTML documents and polyglot HTML documents that must parse correctly as both HTML5 and XML. For modern HTML5-only documents, only lang is needed and xml:lang is not required. Check when auditing documents served as application/xhtml+xml or documents that include both attributes.
Its SKILL.md is about 800 tokens, which your agent loads only when the skill is triggered. The skill folder holds 2 other files, including reference files (for example `references/rule.md`).
It sits in Frontend & Design. The repository describes itself as: 🗂 The essential checklist for modern web development, for humans and AI agents. The licence is MIT.
When your agent uses it
- Applies to XHTML documents and polyglot HTML documents that must parse correctly as both HTML5 and XML
Example prompts
- “/html-xml-lang-mismatch”
What it can do on your machine
Read from SKILL.md and the folder at commit e8d14d0. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md.
From the folder's file list and the shell code blocks in SKILL.md.
Network
Links to these hosts (documentation or services it may open):
frontendchecklist.io
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.
Context cost
HTML XML Lang Mismatch loads about 799 tokens when it runs, and up to ~1.7k if it reads all its reference files. Until then it costs about 82 tokens; SKILL.md has 391 words of instructions outside code blocks.
Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.
Safety
Auto-check passed
The automated check found no risky patterns in SKILL.md.
Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.
SKILL.md
The full file from thedaviddias/Front-End-Checklist at commit e8d14d0, republished under its MIT licence (© thedaviddias). 391 words, ~799 tokens.
Download SKILL.mdSave it as
.claude/skills/html-xml-lang-mismatch/SKILL.md (or your agent's skills folder). This skill also uses 1 other file; get the full folder from GitHub.- name
- html-xml-lang-mismatch
- description
- Use when applies to XHTML documents and polyglot HTML documents that must parse correctly as both HTML5 and XML. For modern HTML5-only documents, only `lang` is needed and `xml:lang` is not required. Check when auditing documents served as application/xhtml+xml or documents that include both attributes.
- metadata.category
- accessibility
- metadata.priority
- medium
- metadata.difficulty
- beginner
- metadata.estimatedTime
- 5
- metadata.source
- frontendchecklist.io
- metadata.url
- https://frontendchecklist.io/rules/accessibility/html-xml-lang-mismatch
Match lang and xml:lang attributes
Screen readers use the lang attribute to select the correct voice profile and pronunciation engine. If lang and xml:lang disagree, XML-based processors (including some EPUB readers and older assistive technologies) may use xml:lang and get a different language than intended — causing text to be read aloud in the wrong language. For example, French text read with an English voice profile produces unintelligible output for French-speaking blind users.
Quick Reference
- If both
langandxml:langare present on<html>, their values must be identical xml:langis only needed for XHTML or polyglot documents (valid as both HTML and XML)- For standard HTML5 documents, only
langis required —xml:langis redundant - The primary language tag must be a valid BCP 47 language code (e.g.,
en,en-US,fr,zh-Hant) - Relates to WCAG 2.1 SC 3.1.1 (Language of Page)
Check
Inspect the <html> element for both lang and xml:lang attributes. If both are present, verify their values are identical (including subtags — en vs en-US is a mismatch). Also verify that the value is a valid BCP 47 language tag. Flag if the values differ in any way.
Fix
If lang and xml:lang are present but differ: update both to the same valid BCP 47 language code matching the primary language of the document content. If this is a standard HTML5 document (served as text/html), remove xml:lang — it is unnecessary. If this is XHTML or a polyglot document, keep both and ensure they are identical.
Show full SKILL.md (146 more words)Show less
Explain
WCAG 2.1 SC 3.1.1 requires that the default human language of each web page can be programmatically determined. The lang attribute on <html> serves this purpose for HTML parsers. The xml:lang attribute serves the same purpose for XML parsers. When a document must be valid as both HTML and XML (polyglot), both attributes must be present and identical. A mismatch means the document claims different languages depending on which parser reads it, which can cause screen readers, translation tools, and spell checkers to use wrong language rules.
Code Review
Review the rendered markup and interactive states that affect Match lang and xml:lang attributes. Flag exact elements, roles, labels, focus behavior, or keyboard interactions that violate the rule, and note how to verify the fix with browser accessibility tooling or assistive tech.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/rules/accessibility/html-xml-lang-mismatch
© thedaviddias, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
SKILL.md and 1 other file (references) in skills/html-xml-lang-mismatch of thedaviddias/Front-End-Checklist.
- SKILL.md
- references/rule.md
Open the folder on GitHubat commit e8d14d0
Compare with similar skills
HTML XML Lang Mismatch next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| HTML XML Lang Mismatch this skillthedaviddias/Front-End-Checklist | 74k | — | ~799 | Automated safety check: Pass | MIT | |
| Web Artifacts Builderanthropics/skills | 180k | 40 repos | ~769 | Automated safety check: Pass | Apache-2.0 | |
| React Doctormakeplane/plane | 61k | 12 repos | ~657 | Automated safety check: Pass | AGPL-3.0 | |
| Impeccablebestofjs/bestofjs | 3.1k | 26 repos | ~2.6k | Automated safety check: Pass | MIT | |
| Figma Design System Builderwarpdotdev/warp | 65k | 2 repos | ~4.4k | Automated safety check: Pass | AGPL-3.0 | |
| Web Interface Guidelines Reviewervercel-labs/openreview | 1.7k | 97 repos | ~308 | Automated safety check: Pass | None |
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Related
Categories
Questions about HTML XML Lang Mismatch
What does HTML XML Lang Mismatch do?
A skill your agent uses when applies to XHTML documents and polyglot HTML documents that must parse correctly as both HTML5 and XML. HTML XML Lang Mismatch is an agent skill from thedaviddias/Front-End-Checklist. Use when applies to XHTML documents and polyglot HTML documents that must parse correctly as both HTML5 and XML.
When should I use HTML XML Lang Mismatch?
HTML XML Lang Mismatch fits situations like: applies to XHTML documents and polyglot HTML documents that must parse correctly as both HTML5 and XML.
How do I install HTML XML Lang Mismatch in Claude Code?
Run `npx skills add thedaviddias/Front-End-Checklist --skill html-xml-lang-mismatch -a claude-code`. Or copy the skill folder (skills/html-xml-lang-mismatch in thedaviddias/Front-End-Checklist) into .claude/skills/html-xml-lang-mismatch in your project. Claude Code loads it when a task matches its description.
How do I install HTML XML Lang Mismatch in Codex?
Run `npx skills add thedaviddias/Front-End-Checklist --skill html-xml-lang-mismatch -a codex`. Or copy the skill folder (skills/html-xml-lang-mismatch in thedaviddias/Front-End-Checklist) into .agents/skills/html-xml-lang-mismatch in your project. Codex loads it when a task matches its description.
Can I use HTML XML Lang Mismatch in Cursor, Gemini CLI or GitHub Copilot?
Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add thedaviddias/Front-End-Checklist --skill html-xml-lang-mismatch -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/html-xml-lang-mismatch, .gemini/skills/html-xml-lang-mismatch, .github/skills/html-xml-lang-mismatch and .opencode/skills/html-xml-lang-mismatch in your project.
What does HTML XML Lang Mismatch need to run?
SKILL.md names no scripts, command-line tools or credentials: HTML XML Lang Mismatch is instructions for the agent only.
Does HTML XML Lang Mismatch access the network?
SKILL.md names 1 domain. As links in the text: frontendchecklist.io. This is read from the text; nothing was executed.
Is HTML XML Lang Mismatch safe to install?
Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.
What licence does HTML XML Lang Mismatch use?
HTML XML Lang Mismatch is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does HTML XML Lang Mismatch use?
About 799 tokens (SKILL.md is roughly 3.2k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 915 tokens, read only when the agent opens those files.
What are the alternatives to HTML XML Lang Mismatch?
Skills that share tags, products or a category with HTML XML Lang Mismatch: Web Artifacts Builder (anthropics/skills, 180k stars), React Doctor (makeplane/plane, 61k stars), Impeccable (bestofjs/bestofjs, 3.1k stars) and Figma Design System Builder (warpdotdev/warp, 65k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains HTML XML Lang Mismatch?
thedaviddias (a GitHub user) maintains it in thedaviddias/Front-End-Checklist, which has 74,421 GitHub stars. The repository holds 390 skills in this directory. The repository was last updated on October 6, 2026.
Source: thedaviddias/Front-End-Checklist on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.