bdBuild is a program that optimizes a browser-based application in order to improve the load-time performance of that application. At its core, bdBuild implements a simple but eligant engine that marshalls a set of resources through a set of gates, causing plugable, resource-dependent transforms to be applied as a prerequisite to passing each gate. Since new/different transforms are plugable, the functionality of the program can be easily extended. Further, the engine allows the transforms to be applied either synchronously or asynchronously. Employing asynchronous transforms for tasks such as reading and writing data results in extremely high performance. This article describes the motivation, design, and use of bdBuild.