We present a novel and versatile online resource named Clothes4all which is a website, web application, and tool likewise, and which can be used to study various aspects of web accessibility. The article elaborates on the tool’s development, its features and possibilities, as well as use and potential methodology. Clothes4all mimics a web shop for clothes and consists as such of a set of coherent web pages that can be freely used, studied, and extended as desired, in particular aiming at user trials. The site’s main feature is that single or multiple accessibility barriers can be injected into or removed from its web pages in a controlled manner. The primary application area of Clothes4all is the testing and validation of accessibility checkers and validators themselves, and hereby the site is expected to eventually contribute to more accessible web pages. A secondary application area is education, as Clothes4all is a great resource to learn about web technologies, web accessibility, assistive technology, user diversity, impairments, and other aspects of online accessibility.