The GridPort toolkit: a system for building Grid portals. Grid portals are emerging as convenient mechanisms for providing the scientific community with familiar and simplified interfaces to the Grid. Our experience in implementing Grid portals has led to the creation of GridPort: a unique, layered software system for building Grid portals. This system has several unique features: the software is portable and runs on most Web servers; written in Perl/CGI, it is easy to support and modify; it is flexible and adaptable; it supports single login between multiple portals; and portals built with it may run across multiple sites and organizations. The feasibility of this portal system has been successfully demonstrated with the implementation of several application portals. We describe our experiences in building this system, including philosophy and design choices. We explain the toolkits we are building, and we demonstrate the benefits of this system with examples of several production portals. Finally, we discuss our experiences with Grid web service architectures.