---
title: "HTML Validation Checks — Lemwatch Help"
description: "Validate your HTML against W3C standards and fix structural issues."
canonical: "https://lemwatch.com/help/html-validation"
source: "https://lemwatch.com"
---
# HTML Validation Checks
> Validate your HTML against W3C standards and fix structural issues.
## HTML Validation Checks
LemWatch validates your pages against W3C HTML standards and flags structural issues that can affect SEO, accessibility, and browser rendering.
### What Gets Checked
- HTML errors — Unclosed tags, missing required attributes, invalid nesting
- Warnings — Deprecated elements, redundant attributes, accessibility hints
- Fatal errors — Malformed markup that prevents proper parsing
- Info messages — Best practice suggestions
### Why HTML Validation Matters
Impact Area — How Invalid HTML Hurts —
**SEO** — Search engines may misinterpret your content structure —
**Accessibility** — Screen readers rely on valid HTML for navigation —
**Browser rendering** — Different browsers handle errors differently —
**Performance** — Invalid markup can trigger additional parser work —
### Results
For each page checked, you'll see:
- Error count — Issues that violate the HTML specification
- Warning count — Non-critical issues and best practice suggestions
- Fatal errors — Critical issues highlighted separately
- Line numbers — Exact location of each issue in your source code
### Common Issues
- Missing alt attributes — All ![]()
elements need alt text
- Unclosed tags — without
causes rendering issues
- Duplicate IDs — Each id attribute must be unique on a page
- Missing lang attribute — helps accessibility and SEO
- Deprecated elements — , ,