Abstract : One of the challenges in web development is to help achieving a good level of quality in terms of code size and runtime performance, for popular domain-specific languages such as XQuery, XSLT, and XML Schema. We present the first IDE augmented with static detection of inconsistent XPath expressions that assists the programmer for simplifying the development and debugging of any application involving XPath expressions. The tool is based on newly developed formal verification techniques based on expressive modal logics, which are now mature enough to be introduced in the process of software development. We further develop this idea in the context of XQuery for which we introduce an analysis for identifying and eliminating dead code automatically. This proof of concept aims at illustrating the benefits of equipping modern IDEs with reasoning capabilities.