WAT-SL is a web-based tool that is dedicated to segment labeling and highly customizable to the labeling task at hand. WAT-SL provides all functionalities to efficiently run and manage segment labeling projects. Its self-descriptive annotation interface requires only a web browser, making it particularly convenient for remote annotation processes. The interface can be easily tailored to the requirements of the project using standard web technologies in order to focus on the specific segment labels at hand and to match the layout expectations of the annotators. At the same time, it ensures that the texts to be labeled remain readable during the whole annotation process. This process is server-based and preemptable at any point. The annotator’s progress can be constantly monitored, as all relevant interactions of the annotators are logged in a simple key-value based plain text format. [demo] [code]