An instrumentation service is described that uses dye injection and filtering in a Session Initiation Protocol (SIP) application server environment. The instrumentation service can provide a flexible mechanism for selectively adding diagnostic code to the SIP application server and the various applications running on it. It can allow flexible selection of locations in the server and application code, at which instrumentation code can be added. The process of adding diagnostic code can be deferred to the time of running the server at the deployment site. The instrumentation service further allows flexible selection of diagnostic actions, which can be executed at selected locations. In various embodiments, the execution of diagnostic code can be dynamically enabled or disabled while the server is running. Also, the behavior of diagnostic code executed at such locations can be dynamically changed while the server is running.