Disclosed is a method for adding performance counters to a .NET application after compilation of the .NET application to Common Intermediate Language code without a requirement for code changes to the original .NET application code or application recompilation from the development side. With regard to a further aspect of a particularly preferred embodiment, the invention may provide a method for adding the performance counters by declarative instrumentation of a .NET application at runtime or compile time, without the need for an application developer to hardcode instrumentation logic into the application. An instrumentation configuration file provides declarative definition for performance counters that are to be added to a particular application, and particularly includes a complete list of performance counters that need to be added and settings for each performance counter.