Modern experiments demand a powerful and efficient Data Acquisition System (DAQ). The intelligent, FPGA-based Data Acquisition System (iFDAQ) of the COMPASS experiment at CERN is composed of many processes communicating between each other. The DIALOG library covers a communication mechanism between processes and establishes a communication layer to each of them. It has been introduced to the iFDAQ in run 2016 and improved significantly the stability of the system. The paper presents the online monitoring API for the DIALOG library. Communication between processes is challenging from a synchronization, reliability and robustness point of view. Online monitoring tools of the communication between processes are capable to reveal communication problems to be fixed in future. The debugging purpose has been crucial during introduction period to the iFDAQ. On the other hand, based on the measurement of communication between processes, the proper load balancing of processes among machines can improve the stability of the system. The online monitoring API offers a general approach for the implementation of many monitoring tools with different purposes. In the paper, it is discussed its fundamental concept, integration to a new monitoring tool and a few examples of monitoring tools are given.