SPIDER: A simple and flexible tool for design and provisioning of protected lightpaths in optical networks. Optical devices are poised to form the core of the next generation of backbone and enterprise networks. Optical routers, dense wavelength division multiplexing (DWDM) systems, and cross connects of unprecedented capacities are on the verge of large-scale commercial deployment. This massive buildup of optical gear necessitates careful planning and provisioning of the basic units of transmission — the light-paths. This paper presents a range of techniques for efficient and reliable optical network design, covering decentralized dedicated protection to shared path-based mesh restoration. These algorithms have been incorporated into SPIDER, an extensible software tool with a browser-based user interface, Java∗-based visualization, and spreadsheet input/output capabilities. We describe SPIDER and report on recent core networking applications using this tool, which also illustrate the key tradeoffs in optical network designs involving a variety of grades of protection and the balance between efficient use of wavelengths and restoration time.