We at Constant Contact have been using Wiztools.org's RESTClient to help us troubleshoot problems with people's code. In particular, if you are receiving a response of '400' from the API, it is likely due to the structure of your XML. This tool is an easy place to GET, edit, PUT and POST XML to various APIs.
RESTClient is a Java platform client application to test RESTful webservices. It can be used to test a variety of HTTP communications.
For more information go here:
authentication
Remember to use API_KEY%USERNAME for username
RE: authentication
Courtesy of one of our Technical Support members, Brad Clark, preemptive must be UNCHECKED in the new 2.3 version of the REST Client. This option previously did not matter in the 2.2 version.
Dave B Support Engineer, Constant Contact
We created a quick user guide
We created a quick user guide for this tool. It can be found at http://developer.constantcontact.com/doc/restclient.
Chang Suh
Product Manager, Constant Contact