The paper focuses on describing and using the unique software tools CEISOQ, supporting the mathematical models of information gathering, storage, processing and producing by computer-based systems 1-2. An application of CEISOQ permits to evaluate a degree of achieving the information systems operation purpose: to meet users requirements for providing reliable, timely, complete, valid and confidential information. Software tools CEISOQ purposed to systems analysts (IS customers, designers, developers, users, experts of testing laboratories and certification bodies, as well as a staff of IS operation quality maintenance) for solving the next system problems: for substantiating framework and specifying quantified system requirements (to hardware, software, users, staff, technologies); for requirements analyzing, technical decisions evaluating, the bottle-necks exposuring; for investigating potential threats to information quality; for testing IS operation; for rational tuning IS technologies parameters.. CEISOQ may be also used in training and education in specialization “Information systems”.