Web Accessibility is a basic attribute of quality in use and a player to a successful Web application. The principles of design called for all or universal design, are aimed at product design and user-friendly environments for as many people as possible, without the need to adapt or redesign it so specially. There are different tools and approaches to assist to the Accessibility evaluation of existing Web applications. In contrast, there are no similar efforts for the early design with Accessibility principles in mind. Designing Web applications to improve Accessibility implies the analysis of different concerns that can be linked through the use of techniques from Aspect-Oriented Software Development (AOSD). In this work we propose a tool’s architecture based on AOSD design concepts and the Web Content Accessibility Guidelines 1.0 (WCAG 1.0) to support building accessible user interfaces.