A program for the online analysis and monitoring of the High Acceptance DiElectron Spectrometer (HADES) is
described. HADES has to be commissioned at GSI (Darmstadt, Germany) using the highest SIS energies and beam intensities. A certain part of the HADES spectrometer is already in operation allowing to carry out intensive hardware and software tests. We present an effective software tool which being a part of the general HADES analysis framework, provides an easy way to perform the direct monitoring of any particular HADES subdetector and also the preliminary online analysis by means of data correlations. This tool allows to
define at run time histogrammes and conditions under which the histogrammes must be filled. The user can both make use of a set of predefined parameters for histogramming or create his own ones also at run time. Conditions can be mathematical expressions, graphical cuts or combinations of both types. There are two
levels of conditions which can be applied to the hits in a particular subdetector (for monitoring purposes) or to the event in the whole for matching the information from different detectors and making all possible types of data correlations. The program has a powerful and ergonomic graphical user interface (GUI) which allows to
easily create and save all histogram and condition definitions, perform event loop and visualize the data. The whole package is a library of approximately 40 classes written in C++ and integrated into the ROOT framework. Several constituents of the program mainly related to the data visualization like for example making slices of two-dimensional histogrammes, are designed in such a way that can be independently used in other applications.