You know what’s incredibly helpful? RequestBin! Why is it so great? Because testing webhooks sucks and RequestBin makes it easy. Logging your output is a good start but that can’t tell you which IP your request is actually coming from. RequestBin can, which is awesome when you’re trying to figure out whether the Elastic IP you set up in AWS is working correctly. It also shows you all of your output (in a nice human-readable format, no less), which is handy if you really want to know exactly what your client receives.
It’s also free! On the downside your destination url only lasts for 48 hours and your data may be wiped out at any time (if you need a permanent solution look at Runscope’s Request Captures – seems only fair to plug the paid version when I’m talking about how helpful the free one is), but the price is right :)