neXSim is a web-based prototype system implementing "implementing a logic based framework for characterising nexus of similarity within knowledge bases", namely expressing in a comprehensive way all the commonalities between tuple of entities (https://doi.org/10.1016/j.ins.2024.120331). The current version of neXSim, implemented in Python through the Flask framework, offers a collection of RESTful APIs implementing the main operations described in the aforementioned framework, such as summaries and characterizations (among the others). The system offers also a web-based user interface developed in Javascript (React), for interacting with the APIs in an immediate and intuitive way, providing an user-friendly visualization of formulas, either via graphs or textual representation.