This presentation describes a network-based simulator for protective relaying algorithms. The simulator is based on the client-server paradigm. The simulator which consists of server-side relaying algorithm modules and the user interface provides the network-based environment to simulate a variety of protective relaying algorithms. It is developed by using open-source development tools and model-based design methods. The relay models implemented have many functional blocks for flexibility. Clients are able to access the simulator through a generic Web browser. The simulator makes it possible for protection engineers, relay developers and students to concentrate on the development and analysis of a protective relaying algorithm in which users are interested.