The paper presents the novel online tool for robust PID controller design RobCont that enables to design robust PID controllers and to analyze the stability of the closed-loop control performance in an advanced way. This tool is an extension of modular system WebPIDDESIGN, a complex framework that provides features of system identification, PID controller design, and evaluation of control quality. RobCont extends the possibilities of framework by control design tasks focused on systems with interval uncertainties. The tool allows user to perform the step-by-step procedure from system definition, through open loop analysis, to selection of robust controller, closed loop simulation, and evaluation of control quality. The controller selection is based on Neimark's D-partition method and Kharitonov's 16 plant theorem. The RobCont extends also other features of the WebPIDDESIGN, i.e. enables to perform the polynomial approximation of the time-delay systems. The paper also contains a case study on a real laboratory process, where common RobCont usage procedure is illustrated. The presented tool is mainly intended for the education purposes in the field of automatic control.