A rewriting web proxy for testing interactions between your browser and external sites.

Billy spawns an EventMachine-based proxy server, which it uses to intercept requests sent by your browser. It has a simple API for configuring which requests need stubbing and what they should return.Billy lets you test against known, repeatable data. It also allows you to test for failure cases. Does your twitter (or facebook/google/etc) integration degrade gracefully when the API starts returning 500s? Well now you can test it!.