One of possible expenditures of reduction and testability process acceleration choices is to increase circuit’s testability. It means to increase controllability and observability of the circuit. As to determine the circuit’s controllability and observability manually takes lots of time, it is meaningful to automate this process. The main purpose is to determine and improve the controllability of the circuit by offering some suggestions to system on chip’s designers how to improve circuit’s controllability. We try to analyze if it is possible to do this only by using created software. This software’s architecture uses client-server mode and all computations are performed on a server side. The system is realized on Apache server with Linux OS. System modules are realized using C++, PHP, JAVA, HTML and JavaScript programming languages. In this paper it is being introduced the definition of controllability, explored methods of controllability estimation and increase. Also there is introduced the research how to improve accuracy of software results. The methods of the controllability estimation for “white box” are modified to work with “black box”. Assumptions made during the research were validated by experiments.