The CCI Metadata API allows applications to efficiently analyze or modify .NET assemblies, modules, and debugging (PDB) files. CCI Metadata supports the functionality of the .NET System.Reflection and System.Reflection.Emit APIs, but with much better performance. It also provides additional functionality that is not available in either .NET API.
CCI was created by Microsoft Research, and is currently not under active development and Microsoft is recommending using other tools (e.g. Roslyn).