This includes requests, responses and the HTTP headers (which contain the cookies and caching information).

It acts as a man-in-the-middle for HTTP/SSL connections, enabling to debug the content of HTTPS sessions and packets. 

Charles simulates modem speeds by effectively throttling your bandwidth and introducing latency, so that you can experience an entire website as a modem user might (bandwidth simulator).

Charles is especially useful for Adobe Flash developers as you can view the contents of LoadVariables, LoadMovie and XML loads. Charles also has native support for Flash Remoting (AMF0 and AMF3). More about Charles and Flash.

Charles is also useful for XML development in web browsers, such as AJAX (Asynchronous Javascript and XML) and XMLHTTP, as it enables you to see the actual XML that is flowing between the client and the server. Charles natively supports JSON, JSON-RPC and SOAP; displaying each in a simplified tree format for easy viewing and debugging.

Charles will autoconfigure the browser's proxy settings on the following browsers:
- IE (Windows system proxy settings)
- Firefox
- Safari (Mac OS X or Windows system proxy settings)

Here are some key features of "Charles":

· Validate recorded HTML, CSS and RSS/atom responses using the W3C validator
· 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

What's New in This Release: [ read full changelog ]

Major bug fixes:
· Java 1.7 now supported. Corrects slow startup and hung responses bugs.
· Java 1.7 bad certificate error workaround for sites that use now disabled algorithms (ie. MD2withRSA)
· Windows: Fix launching Charles by opening a file
· SSL empty requests regression from 3.6.4 fixed
· SSL now records the correct remote address details
· SSL errors now more consistently displayed in the browser
· Authentication header viewer can now recover from slightly oddly formatted headers
· Closed connections regression from 3.6.4 fixed

Other changes:
· Double-clicking a request no longer switches Structure and Sequence view. I did this too many times accidentally. The contextual menu now has an option to switch.