I’ve been a long-time fan of RequestBin, but it’s no longer active since it suffered so much bad traffic. It’s never been too difficult to set up locally and when I tried to do that last week, I realised it has got even easier because it now has a docker-compose configuration.
RequestBin, in case you’re not familiar with it, is a tool that will create “request bins," unique URLs that you can send HTTP traffic to. It also provides a web interface where you can go and inspect the requests that were sent, so it’s an excellent tool for testing HTTP clients, buggy API requests… all sorts of things. It’s been offered as a hosted service in the past which I guess is a convenient and quick way to get started with something, but it’s almost as quick to set it up locally.