I recently did some extensive work on using the download tool to invoke Restful Web Services. A lot of the initial effort was around ensuring that the data being passed in the header and body for the request was as the service required. Following review of experiences on the community I used a tool called Fiddler to directly view what was being sent to identify the problems in my transformations of the data going into the Download tool. The idea is that the raw HTTP request and reply messages are available directly in Alteryx in the Results window when running a workflow, preventing the need to use another tool.