WebChecker is a plugin for Epsilon Validation Language (EVL), designed to validate both static and dynamic HTML pages utilizing frameworks like Bootstrap. By employing configurable EVL constraints, WebChecker enforces implicit rules governing HTML and CSS frameworks. The effectiveness of the plugin is demonstrated through its application on Bootstrap, the widely adopted HTML, CSS, and JavaScript framework. WebChecker comes with a set of EVL constraints to assess Bootstrap-based web pages. To substantiate our claims, I present an illustrative example featuring two solutions that effectively enforce implicit rules.