What tools help check HTML semantics?

HTML semantics can be checked with tools that analyze the structure, accessibility, and correctness of markup. They find errors, warnings, and give recommendations for improving code from the point of view of semantics, accessibility, and SEO.

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#1. W3C Markup Validation Service

The official HTML validator from the W3C consortium. Checks whether a page complies with HTML standards and whether there are errors in tags or their nesting.

Site: https://validator.w3.org Shows:

• invalid tags and attributes,
• structural errors (for example, a <section> without a heading),
• deprecated elements.

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#2. Lighthouse (built into Chrome DevTools)

A tool from Google for auditing web page quality: SEO, performance, accessibility, and semantics.

How to run it:

1. Open the site in Google Chrome.
2. Press F12 → Lighthouse.
3. Run the analysis.

Shows:

• the correctness of headings (<h1>-<h6>),
• the structure of semantic tags (<main>, <nav>, <footer> and others),
• accessibility issues (for example, a missing alt on images).

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#3. axe DevTools

A browser extension (Chrome, Firefox) developed by Deque Systems. Focused on auditing accessibility and semantics.

Site: https://www.deque.com/axe/ Checks:

• the correct use of roles and tags,
• the presence of aria attributes,
• the correct use of interactive elements.

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#4. HTMLHint

A tool for static analysis of HTML code that can be integrated into editors like VS Code.

Site: https://htmlhint.com/ Checks:

• the structure of the document,
• the nesting of tags,
• deprecated or incorrect attributes.

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#5. Wave Evaluation Tool

An online service and browser extension created by WebAIM that checks the accessibility and semantic correctness of a page.

Site: https://wave.webaim.org Shows visually:

• where alt, label, or headings are missing,
• where the structure is broken,
• which elements have no semantic meaning.

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#6. Pa11y

A CLI tool (for the terminal) that checks pages for accessibility and semantic errors. Useful for automated tests and CI/CD.

Site: https://pa11y.org

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#Summary:

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Conclusion: The combination of W3C Validator + Lighthouse + axe gives the most accurate picture: they find errors in markup, missing semantic tags, accessibility issues, and an incorrect heading hierarchy.