On Windows, Fiddler is a popular tool to inspect HTTP traffic. On Mac and XCode, you can inspect the content of HTTP traffic using the Open Web Application Security Project (OWASP) WebScarab tool.

Installation:
Download and install WebScarab by running the maven or ant build install file. This should produce a webscarab.jar file in the root directory. To run it:

local$ java -jar webscarab.jar


On your Mac go to > System Settings > Network > and select your internet connection, then go to the Advanced… settings. Click the Proxies tab and select ‘Web Proxy (HTTP)’. For Web Proxy Server enter ‘127.0.0.1’ on Port 8008, which is the port WebScarab by default is configured to listen. You can add addresses to bypass the proxy, as many system requests will run on your machine: e.g. *.local, metrics.apple.com, mybrowserbar.com, pixel.adsafeprotected.com, www.gstatic.com, clients2.google.com.

In the WebScarab Proxy tab, go to the Listeners section and make sure that a listener has been added for Address 127.0.0.1 and Port 8008.

In WebScarab go back to the Summary tab to start inspecting HTTP traffic requests and responses. If you double click a single request in the bottom half of your Summary window, a new window will open, with request and response message respectively on top and below. Toggle between Parsed and Raw to see the messages in table or text form.