JTidy.sourceforge.net The Core of this application.
TWINE twineproject.sourceforge.net Toolkit for Web-Interface Evaluation.
A set of Java and PHP components for allowing dynamic web application interfaces to be submitted to online HTML and Accessibility validation services, allowing for standards-based HTML problems to be easily identified.
CSS Validator The W3C CSS Validation Service; a free service that checks Cascading Style Sheets (CSS) in (X)HTML documents or standalone for conformance to W3C recommendations. Java source is available for download.