Performance issues are vital to the success of many interactive software systems, including software development tools and Web-based tools. However, the issue of performance engineering is still not emphasized in the process of software development. The key aim of this paper is to illustrate an effective method to achieve satisfactory performance for interactive software after careful design. This paper presents how to apply the software performance engineering (SPE) method by focusing on performance estimation at the design stage, and its effect on determining implementation approaches, in the development of interactive software tools. In addition to the rigid quantitative estimation method originated from SPE, this paper argues that the performance can also be cost-effectively estimated either semi-quantitatively or non-quantitatively. With the experience results described in this paper, it is suggested that it may not be compulsory to achieve direct quantitative performance estimation from environment specifications for every software development as advocated by the SPE method. This paper demonstrates a combination of analytical and experimental approaches to assessing the performance at early stages in development of software tools.