scip-ruby is an open source indexer that lets you browse Ruby code online, with IDE functionality like “Go to definition” and “Find usages”. We originally built scip-ruby to improve Ruby support in Sourcegraph, a code intelligence platform. In this talk, you will learn how we built scip-ruby on top of Sorbet, a Ruby typechecker, and how scip-ruby compares to IDEs and other online code navigation tools. Along the way, we will discuss how quintessential ideas like layering code into a functional core and an imperative shell apply to developer tools, and enable easier testing.