Ratproxy is a semi-automated, largely passive web application security audit tool. It is meant to complement active crawlers and manual proxies more commonly used for this task, and is optimized specifically for an accurate and sensitive detection, and automatic annotation, of potential problems and security-relevant design patterns based on the observation of existing, user-initiated traffic in complex web 2.0 environments.
The proxy analyzes problems such as cross-site script inclusion threats, insufficient cross-site request forgery defenses, caching issues, potentially unsafe cross-domain code inclusion schemes and information leakage scenarios, and much more.
There are numerous alternative proxy tools meant to aid security auditors – most notably WebScarab, Paros, Burp, ProxMon, and Pantera. Stick with whatever suits your needs, as long as you get the data you need in the format you like.
That said, ratproxy is there for a reason. It is designed specifically to deliver concise reports that focus on prioritized issues of clear relevance to contemporary web 2.0 applications, and to do so in a hands-off, repeatable manner. It should not overwhelm you with raw HTTP traffic dumps, and it goes far beyond simply providing a framework to tamper with the application by hand.
You can download Ratproxy here:
Or read more here.
The tool should run on Linux, *BSD, MacOS X, and Windows (Cygwin). Since it is in beta, there might be some kinks to be ironed out, and not all web technologies might be properly accounted for.