mitmproxy is an interactive SSL-capable intercepting HTTP proxy, which lets you to observe, modify and replay requests and responses on the fly. The underlying library that mitmproxy is built on can also be used to do these things programmatically.
By default, mitmproxy starts up with a mutt-like interactive curses interface - the help page (which you can view by pressing "?") should tell you everything you need to know. Note that requests and responses are stored in-memory until you delete them, so leaving mitmproxy running indefinitely or requesting very large amounts of data through it is a bad idea.
The first time mitmproxy is started, it will generate a bogus SSL certificate (the default location is ~/.mitmproxy/cert.pem). This certificate will be used for the browser-side of intercepted traffic. Because it won't match any domain you visit, and won't verify against any certificate authority, you will have to add an exception for each site you visit. SSL requests are intercepted by simply assuming that all CONNECT requests are https. The connection from the browser is wrapped in SSL, and we read the request by pretending to be the connecting server. We then open an SSL request to the destination server, and replay the request.
* SSL certificates are generated using [openssl](http://www.openssl.org/)
* The curses interface relies on a current version of the [urwid](http://excess.org/urwid/) library.
* The test suite uses the [pry](http://github.com/cortesi/pry) unit testing library.
You should also make sure that your console environment is set up with the following:
* EDITOR environment variable to determine the external editor.
* PAGER environment variable to determine the external pager.
* Appropriate entries in your mailcap files to determine external viewers for request and response contents.