HTML Validation

Valid HTML is more likely to work consistently across browsers and assistive technologies. Learn to validate and fix common errors.

What is Valid HTML?

Valid HTML:

• Follows the HTML specification
• Has proper document structure
• Uses elements correctly
• Has no syntax errors

Common Validation Errors

Fixed versions:

Nesting Rules

Key nesting rules:

• Block elements can contain inline and block
• Inline elements can only contain inline
• <p> cannot contain block elements
• Lists need <li> as direct children

Deprecated Elements

Use CSS instead of deprecated elements.

Required Elements

W3C Validator

The W3C provides a free online validator:

• URL: https://validator.w3.org/
• Paste HTML or enter URL
• Shows errors and warnings
• Explains how to fix issues

Common error types:

• Error: Must be fixed (breaks validity)
• Warning: Should be fixed (best practice)
• Info: Suggestions for improvement

Self-Validation Checklist

Before validating, check:

Exercise: Fix Validation Errors

Fix all the validation errors in this HTML:

Valid HTML is the foundation of a reliable, accessible website!