Charles is an HTTP proxy/HTTP monitor/Reverse Proxy that enables a developer to view all of the HTTP and SSL/HTTPS traffic between their machine and the Internet. This includes requests, responses and the HTTP headers- which contain the cookies and caching information.

Features:
SSL Proxying – view SSL requests and responses in plain text.
Bandwidth Throttling to simulate slower Internet connections including latency.
AJAX debugging – view XML and JSON requests and responses as a tree or as text.
AMF – view the contents of Flash Remoting / Flex Remoting messages as a tree.
Repeat requests to test back-end changes.
Edit requests to test different inputs.
Breakpoints to intercept and edit requests or responses.