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.
First: clone the repository https://github.com/Runscope/requestbin
Then, you'll need Docker Compose to run the next commands:
docker-compose build docker-compose up
When those commands complete, you will find a RequestBin running at http://localhost:8080 - Happy HTTP request testing :)