#092 · HTML Developer Tool

HTML Checker

Check HTML structure, SEO essentials, accessibility basics, and semantic markup in one local browser tool. The checker reports passed items, warnings, and errors for common issues such as duplicate IDs, missing image alt text, absent metadata, and heading-order problems.

Developer Input

HTML quality checks

HTML source

<!doctype html>
<html lang="en">
<head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1"><title>Sample page</title><meta name="description" content="A sample HTML page for testing."></head>
<body><main><h1>Sample page</h1><img src="photo.jpg" alt="Sample photo"><p>Hello world.</p></main></body>
</html>

Check profile

Minimum score

Trim outer whitespace Include passed checks Run complete validation Auto-run while typing

How to use this developer tool

Paste or type the source content in the main editor.
Choose the processing mode and adjust the tool-specific option.
Enable or disable the validation and live-processing options as needed.
Select the primary action, review the report and statistics, then copy or download the result.

What this developer tool does

Check HTML for common structural, SEO, accessibility, semantic, and mobile-readiness issues in your browser.

Parse DOM → run structural, SEO, accessibility, and semantic checks → calculate a practical quality score.

All processing occurs locally in the browser. Review automated findings before using the result in production.

Example

The editor is preloaded with a working HTML Checker example. Change the sample, select an option, and run the tool to compare the input with the generated output and report.

Tips for better output

Use a complete document when checking SEO essentials.
Treat warnings as review items, not guaranteed defects.
Recheck after correcting duplicate IDs and heading order.

FAQ

Why is my HTML failing quality checks?

The report separates structural errors from SEO, accessibility, and semantic warnings so you can identify the specific failed checks.

How do I detect duplicate IDs in HTML?

Run the complete or structure-focused audit. Every repeated non-empty id value is listed as an error.

How can I check missing alt text in HTML images?

Use the accessibility-focused or complete audit. Images without useful alt attributes are reported.

Which HTML meta tags should every page include?

A practical page should normally include charset, viewport, title, and description; canonical and social metadata are recommended where appropriate.

Can I check a full HTML document locally?

Yes. Paste the entire document. Parsing and analysis occur in the browser without uploading the source.

Related developer tools

HTML Generator HTML Converter HTML Parser HTML Validator

HTML Checker modules

Module	Details
Structure	Document and element checks
SEO	Title, description, canonical, social tags
Accessibility	Alt text, labels, headings, language
Output	Scored audit report

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