HTML Validator

Validate HTML online using W3C standards. Check any URL or paste HTML code to find errors, warnings, and accessibility issues with line numbers.

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APIPOST /api/v1/web/validate
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Try also: Speed Test
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Key Features

100% Free

No registration required, unlimited checks

Instant Results

Real-time analysis with detailed output

REST API Access

Integrate into your workflow via API

Accurate Data

Live queries to authoritative sources

What is HTML Validator?

The HTML Validator checks your web pages against W3C standards. It finds markup errors, missing attributes, unclosed tags, deprecated elements, and accessibility issues. Valid HTML improves SEO, cross-browser compatibility, and page rendering performance.

How to Use

  1. 1Enter a URL or paste your HTML code
  2. 2Choose URL mode to validate a live page, or HTML mode to paste code directly
  3. 3Click Validate to run the W3C check
  4. 4Review errors and warnings with line numbers and code excerpts

Who Uses This

System Administrators

Monitor and troubleshoot infrastructure

Developers

Debug network issues and integrate via API

SEO Specialists

Verify domain configuration and performance

Security Analysts

Audit and assess network security

Frequently Asked Questions

Why should I validate my HTML?
Valid HTML ensures your pages render correctly across all browsers, improves SEO rankings, helps screen readers parse content for accessibility, and reduces unexpected layout issues. Search engines prefer well-structured HTML.
What is W3C validation?
W3C (World Wide Web Consortium) sets the standards for HTML. Their validator checks if your markup follows the official HTML specification, catching errors like unclosed tags, invalid attributes, and deprecated elements.
Does HTML validation affect SEO?
While Google doesn't require perfect HTML, valid markup helps search engines parse and index your content correctly. Broken HTML can cause rendering issues, hide content from crawlers, and negatively affect Core Web Vitals scores.

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API Endpoint

POST /api/v1/web/validate
View Documentation