html-xml-lang-mismatch

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.

Quality

63%

Does it follow best practices?

Run evals on this skill

Adds up to 20 points to the overall score

View guide

Securityby

Passed

No findings from the security scan

Fix and improve this skill with Tessl

tessl review fix ./skills/html-xml-lang-mismatch/SKILL.md

Quality

Content

70%

Reviews the quality of instructions and guidance provided to agents. Good implementation is clear, handles edge cases, and produces reliable results.

The body is well-structured with a clear single-task workflow and clean one-level-deep progressive disclosure to a real reference file, but it carries some redundant rationale and templated boilerplate, and pushes the executable examples out of the body.

Suggestions

Tighten or remove the generic 'Code Review' boilerplate paragraph, replacing it with the specific verification steps for this rule.

Fold a minimal inline correct/incorrect code snippet (the html lang/xml:lang examples) into the Check or Fix section so the body is self-contained, keeping the reference for deeper detail.

Trim the overlapping WCAG rationale between the intro and the Explain section to a single concise justification.

Dimension	Reasoning	Score
Conciseness	The body is mostly lean and well-sectioned, but the intro/Explain paragraphs re-explain WCAG rationale and the templated 'Code Review' boilerplate ('Review the rendered markup and interactive states that affect...') adds padding without earning its tokens.	2 / 3
Actionability	The Check and Fix sections give concrete, specific guidance (subtag matching like en vs en-US, BCP 47 validation, text/html vs XHTML branching), but executable code examples are deferred to references/rule.md rather than present inline, leaving the body short of copy-paste-ready depth.	2 / 3
Workflow Clarity	A simple single-task skill sequenced clearly (Quick Reference -> Check -> Fix -> Explain -> Code Review), with a verification checkpoint ('note how to verify the fix with browser accessibility tooling or assistive tech'), meeting the simple-skill bar of an unambiguous action.	3 / 3
Progressive Disclosure	The body is a well-organized overview that signals a single one-level-deep reference ('see references/rule.md') for full implementation details and code examples, and that referenced file is real and not further nested.	3 / 3
	Total	10 / 12 Passed

Description

57%

Based on the skill's description, can an agent find and select it at the right time? Clear, specific descriptions lead to better discovery.

The description targets a clear, narrow niche with explicit triggers and low conflict risk, but it leads with 'when' framing and leaves the concrete 'what does this skill do' action implied, and its trigger terms skew technical rather than natural.

Suggestions

Lead with a crisp capability statement (e.g., 'Verify that lang and xml:lang on <html> have identical valid BCP 47 values') before the 'Use when' trigger clause so the 'what' is explicit.

Add natural-language trigger variations users would actually say, such as 'language attribute mismatch' or 'screen reader reading the wrong language'.

Smooth the awkward 'Use when applies to...' phrasing into a natural third-person trigger sentence.

Dimension	Reasoning	Score
Specificity	Names a concrete domain (XHTML, polyglot, HTML5/XML parsing) and several specific audit contexts, but the actual action is essentially one ('Check when auditing...') rather than a list of multiple distinct concrete actions, so it stops short of the score-3 anchor.	2 / 3
Completeness	Explicit 'when' triggers are present ('Use when...', 'Check when auditing...'), satisfying the cap rule, but the 'what' capability is only implied through that framing rather than stated as a distinct concrete action, so one of the two halves is implicit.	2 / 3
Trigger Term Quality	Relevant technical terms appear ('XHTML', 'polyglot', 'lang', 'xml:lang', 'application/xhtml+xml'), but the phrasing leans technical and omits more natural user-facing variations like 'language attribute mismatch' or 'wrong language in a screen reader'.	2 / 3
Distinctiveness Conflict Risk	The niche is very specific (lang/xml:lang agreement in XHTML/polyglot documents) with distinct triggers that are unlikely to fire for unrelated skills.	3 / 3
	Total	9 / 12 Passed

Validation

93%

Warnings & errors only

Checks the skill against the spec for correct structure and formatting. All validation checks must pass before discovery and implementation can be scored.

Validation — 15 / 16 Passed

Validation for skill structure

Criteria	Description	Result
metadata_version	'metadata.version' is missing	Warning

	Total	15 / 16 Passed

Repository: thedaviddias/Front-End-Checklist
Path: skills/html-xml-lang-mismatch/SKILL.md
Commit: 48405aa

Reviewed: about 12 hours ago

Table of Contents

Discovery Implementation Validation

Is this your skill?

If you maintain this skill, you can claim it as your own. Once claimed, you can manage eval scenarios, bundle related skills, attach documentation or rules, and ensure cross-agent compatibility.