API documentation, as we all know, is rarely comprehensive and almost never up-to-date. An alternative way to get to know an API is by intercepting API calls from a mobile app and examining how they work. Here Jan Schwoebel over at his blog will show you how you can easily do that for iOS apps.
First thing you’ll need to do is download the Charles Proxy, a web debugging proxy app perfect for the task. Install and start Charles. Then configure its proxy settings so you can use it with your iOS app.
Starting Charles Proxy on your iPhone
Next, you’ll need to configure the proxy on your iPhone. Go to Settings -> Wi-Fi -> Wi-Fi name -> Set HTTP Proxy and set it to manual like so.
Record API calls
Then start recording calls in Charles and play with your iOS app. You should see then all the HTTP/HTTPS calls being recorded under Structure. You can then look at each call, examining the details of the request and the response.
Jan recommends filtering by specific URL in Charles Proxy recording settings to limit the number of calls being intercepted to only those that interest you.