This talk presents Orchestrion, a tool that we are developing at Datadog for the automatic instrumentation of Go source code. There are other tools (some open source) that add tracing information to Go programs. What makes Orchestrion’s design interesting is that it’s meant to be extensible, both in how it can find what should be instrumented and in where it can output its instrumentation information. We will cover why a tool like this is necessary, how it was built, and what makes it different from other similar tools that are available. What’s more important than the actual tool is the set of techniques that are used to produce it. Several important software engineering concepts will be discussed, including how to parse a programming language, how to build a tool that analyzes source code, what distributed tracing is and why it’s important, and the power of annotations to represent cross-cutting concerns.