In this paper, we present an abstract framework for Web site verification which improves the performance of a previous, rewriting-based??Web verification methodology. The approximated framework is formalized as a source-to-source transformation which is parametric w.r.t. the chosen abstraction. This transformation significantly reduces the size of the Web documents by dropping or merging contents that do not influence the??properties to be checked. This allows us to reuse all verification facilities of the previous system WebVerdi-M to efficiently analyze Web sites. In order to ensure that the verified properties are not affected by the abstraction, we develop a methodology which derives the abstraction of Web sites from their Web specification. An experimental implementation shows a huge speedup w.r.t. a??previous methodology which did not use this transformation.