Time pressure and quality issues bring new challenges for developing web-based systems. The ability to analyze quality early in the development life cycle is crucial. Among the techniques suggested by the literature, few of them actually support early quality activities when little information about the system is available. We take robustness as a critically important quality attribute, and present a framework for performing robustness assessment during the analysis and architecture design stages. Firstly we use Jacobson's analysis method to decompose a web-based system into subsystems, which then are partitioned into software modules. Then for each module, we apply a simplified FMEA method to find robustness-related failure modes, possible causes, their effects, and furthermore, we identify possible ways to prevent or reduce robustness failures. In the end, we illustrate the proposed method through an example from a simple web-based Internet Bookstore system.