About ValidateHTML
ValidateHTML is a free online tool that helps developers, designers, and content creators validate their HTML and CSS code against modern web standards and best practices.
Why We Built This
Writing clean, valid code is fundamental to building accessible, SEO-friendly, and cross-browser compatible websites. Yet many existing validators feel outdated or overly complex. We wanted to create a fast, modern, and developer-friendly tool that makes validation effortless.
What We Check
- HTML5 specification compliance
- CSS syntax and property validation
- Missing or incorrect attributes
- Deprecated elements and attributes
- Incorrect tag nesting
- Accessibility issues (alt text, heading hierarchy, ARIA)
- Best practices and code quality
Our Quality Score
Every validation produces a quality score from 0 to 100, with a letter grade (A through F). The score is based on the number of unique issue types found, not on how many times each one occurs. Each distinct error type multiplies the score by 0.85, so one error scores 85 and two score 72, and the number keeps moving however many you have rather than bottoming out. Each distinct warning type costs 3 points, capped at 15 in total, so best-practice advice can never drag valid code below a B. Repeated occurrences of the same issue don't stack, so the score reflects the variety of problems, not just the count.
Privacy
Your code is processed on our servers for validation and is not stored, logged, or shared. See our Privacy Policy for details.
Contact
Have feedback or found a bug? Reach out at contact@validatehtml.com.