Diagnostic software tools for large commercial buildings are being developed to help detect and diagnose energy and other performance problems with building operations. These software applications utilize energy management control system (EMCS) trend log data. Due to the recent development of diagnostic tools, there has been little detailed comparison among the tools and a limited awareness of tool capabilities by potential users. Today, these diagnostic tools focus mainly on air handlers, but the opportunity exists for broadening the scope of the tools to include all major parts of heating, cooling, and ventilation systems in more detail. This paper compares several tools in the following areas: Scope, intent, and background - Data acquisition, pre-processing, and management - Problems detected - Raw data visualization - Manual and automated diagnostic methods - Level of automation This comparison is intended to provide practitioners and researchers with a picture of the current state of diagnostic tools. There is tremendous potential for these tools to help improve commercial building energy and non-energy performance.