See how it works at http://beebole.com/blog/general/sandbox-your-cross-domain-jsonp-to-improve-mashup-security/ There are 2 implementations of the sandbox: PHP: at http://beebole-sandbox.com (small example server) The directory is sandbox/ PYTHON: at http://beebole-sandbox.appspot.com (hosted on the Google App Engine servers) The directory is google_appengine/