What is HTML Validation?
HTML validation checks your markup for syntax errors, structural issues, and best practice violations. While browsers are forgiving of HTML errors, valid HTML ensures consistent rendering, better accessibility, and maintainable code.
This validator catches common issues like unclosed tags, deprecated elements, and missing attributes that could cause problems.
What Gets Checked
The validator looks for:
- Unclosed tags (missing closing tags)
- Mismatched opening/closing tags
- Deprecated HTML elements
- Missing DOCTYPE declaration
- Missing alt attributes on images
- Basic document structure
Why Valid HTML Matters
Valid HTML renders consistently across browsers. It's easier for screen readers to parse, improving accessibility. It's also easier for other developers to maintain.
Search engines may parse valid HTML more reliably. And debugging is simpler when your markup follows standards.
Frequently Asked Questions
What does HTML validation check?
HTML validation checks for proper tag syntax, matching opening/closing tags, correct nesting, valid attribute usage, and overall document structure.
What are common HTML errors?
Common errors include: unclosed tags, mismatched tags, deprecated elements, missing required attributes (like alt on images), incorrect nesting (like <p><div></div></p>).
Does my HTML need to be 100% valid?
Browsers are forgiving, but valid HTML ensures consistent rendering across browsers, better accessibility, and easier debugging. It's a best practice for production code.
What about HTML5 doctype?
<!DOCTYPE html> should be the first line of HTML5 documents. It tells browsers to use standards mode. Missing it can trigger quirks mode with inconsistent behavior.